Frontiers in Quantum Materials and Devices Workshop 2016
Talk Abstracts
Weyl Wiggles: Exotic Quantum Oscillatory Phenomena in Weyl and Dirac Semi-Metals
James Analytis
University of California, Berkeley
Dirac semi-metals show a linear electronic dispersion in three dimensions described by two copies of the Weyl equation, a theoretical description of massless relativistic fermions. At the surface of a crystal, the breakdown of fermion chirality is expected to produce topological surface states without any counterparts in high-energy physics nor conventional condensed matter systems, the so-called “Fermi Arcs”. Here we present Shubnikov-de Haas oscillations in Focused Ion Beam prepared microstructures of Cd3As2 that share characteristics of surface and bulk states as expected for “Weyl orbits”, the theoretically predicted cyclotron path that weaves together Fermi arc and chiral bulk states. In contrast to conventional cyclotron orbits, these are governed by the chiral bulk dynamics rather than the common momentum transfer due to the Lorentz force. Our observations provide evidence for direct access to the Fermi Arc surface states in a transport experiment, a first step towards their potential application.
James Analytis
University of California, Berkeley
Dirac semi-metals show a linear electronic dispersion in three dimensions described by two copies of the Weyl equation, a theoretical description of massless relativistic fermions. At the surface of a crystal, the breakdown of fermion chirality is expected to produce topological surface states without any counterparts in high-energy physics nor conventional condensed matter systems, the so-called “Fermi Arcs”. Here we present Shubnikov-de Haas oscillations in Focused Ion Beam prepared microstructures of Cd3As2 that share characteristics of surface and bulk states as expected for “Weyl orbits”, the theoretically predicted cyclotron path that weaves together Fermi arc and chiral bulk states. In contrast to conventional cyclotron orbits, these are governed by the chiral bulk dynamics rather than the common momentum transfer due to the Lorentz force. Our observations provide evidence for direct access to the Fermi Arc surface states in a transport experiment, a first step towards their potential application.
Metal-Graphene Hybrids as a Model System for 2D Superconductivity
Vincent Bouchiat
Neel Institute, CNRS-Grenoble, Grenoble, France.
e-mail: [email protected]
Graphene provides a ideal 2D gas of Dirac Fermions which is directly exposed to the environment. Therefore it provides an ideal platform on which to tune, via application of an electrostatic gate, the coupling between electronically ordered adsorbates deposited on its surface. This situation is particularly interesting when the network of adsorbates can induce some electronic order within the underlying graphene substrate, such as magnetic or superconducting correlations [1]. To demonstrate this concept, we have measured arrays of superconducting clusters physisorbed on Graphene capable to induce via the proximity effect a gate-tunable superconducting transition. We have experimentally studied the case of macroscopic graphene decorated with an array of superconducting tin clusters [2], which induce via percolation of proximity effect a global but tunable 2D superconducting state. By adjusting the graphene disorder and its charge carrier density on one side , the geometrical order, cluster size and density of the superconducting dot network on the other side, the superconducting state can exhibit very different behaviors, allowing to test different regimes and quantum phase transition from a granular superconductor to either metallic or insulating states, leading to a bosonic-type gate-controlled quantum phase transition [3]. I will show recent experimental results involving three sets of triangular arrays sparsely distributed on graphene, in which superconductivity is destroyed for a critical gate value that we attribute to the effect of quantum fluctuations of the phase giving rise to an intermediate metallic state [4].
References
Vincent Bouchiat
Neel Institute, CNRS-Grenoble, Grenoble, France.
e-mail: [email protected]
Graphene provides a ideal 2D gas of Dirac Fermions which is directly exposed to the environment. Therefore it provides an ideal platform on which to tune, via application of an electrostatic gate, the coupling between electronically ordered adsorbates deposited on its surface. This situation is particularly interesting when the network of adsorbates can induce some electronic order within the underlying graphene substrate, such as magnetic or superconducting correlations [1]. To demonstrate this concept, we have measured arrays of superconducting clusters physisorbed on Graphene capable to induce via the proximity effect a gate-tunable superconducting transition. We have experimentally studied the case of macroscopic graphene decorated with an array of superconducting tin clusters [2], which induce via percolation of proximity effect a global but tunable 2D superconducting state. By adjusting the graphene disorder and its charge carrier density on one side , the geometrical order, cluster size and density of the superconducting dot network on the other side, the superconducting state can exhibit very different behaviors, allowing to test different regimes and quantum phase transition from a granular superconductor to either metallic or insulating states, leading to a bosonic-type gate-controlled quantum phase transition [3]. I will show recent experimental results involving three sets of triangular arrays sparsely distributed on graphene, in which superconductivity is destroyed for a critical gate value that we attribute to the effect of quantum fluctuations of the phase giving rise to an intermediate metallic state [4].
References
- M. Feigel’man et al. JETP Lett., 88, 747, (2008).
- B.M.Kessler, et al., Phys. Rev. Lett 104, 047001 (2010).
- Adrien Allain, et al. Nature Materials, 11, 590–594, (2012).
- Zheng Han, et al., Nature Physics, 10, 380, (2014).
Electronic Materials with Frustrated Lattices
Joseph Checkelsky
Massachusetts Institute of Technology
Geometrically frustrated lattices give rise to electronic correlation that results in complex magnetic orderings, quantum spin liquid ground states, and other emergent phases. While such systems are typically electronic insulators constructed from low connectivity lattices, recently a variety of frustration-related effects have been explored in systems that have itinerant electrons. Examples include lattice model realizations of the fractional quantum Hall effect and superconductors with exotic pairing symmetries. Here I will present our experiments using itinerant electrons to probe the behavior of kagome, triangular, and related frustrated lattice systems. Electronic transport is found to be a complementary probe to magnetic and scattering experiments. The Hall effect in particular acts as an incisive diagnostic for complex magnetic orderings. I will discuss the prospects for future experiments that build on these findings to realize model frustrated systems.
Joseph Checkelsky
Massachusetts Institute of Technology
Geometrically frustrated lattices give rise to electronic correlation that results in complex magnetic orderings, quantum spin liquid ground states, and other emergent phases. While such systems are typically electronic insulators constructed from low connectivity lattices, recently a variety of frustration-related effects have been explored in systems that have itinerant electrons. Examples include lattice model realizations of the fractional quantum Hall effect and superconductors with exotic pairing symmetries. Here I will present our experiments using itinerant electrons to probe the behavior of kagome, triangular, and related frustrated lattice systems. Electronic transport is found to be a complementary probe to magnetic and scattering experiments. The Hall effect in particular acts as an incisive diagnostic for complex magnetic orderings. I will discuss the prospects for future experiments that build on these findings to realize model frustrated systems.
Integer and Fractional Quantum Hall Effect in Suspended Graphene in Corbino Geometry
Pertti Hakonen
Low Temperature Laboratory, Department of Applied Physics, Aalto University, Espoo, Finland
We have succeeded in manufacturing high-quality suspended graphene samples in Corbino geometry. The Corbino geometry offers two important advantages when compared with standard quantum Hall bars. First, the longitudinal conductivity results can be directly compared with theory, without any need of a matrix inversion like in the case of Hall bar measurements. Second, it improves the resolution in the transport measurement regime where the longitudinal conductance is very small. These are important factors for our experiments aiming at shot noise mapping of charge carries in the fractional quantum Hall state of graphene.
In addition to electrical conductivity and noise, we have determined fundamental mechanical modes of our monolayer graphene Corbino device. In conductance experiments up to 9T field, we can clearly see the fractional states with filling factors 1/3 and 2/5. The mechanical resonance frequency is employed to yield additional information on the carrier density and dynamics near the integer and fractional QHE levels. In order to find out whether shot noise data in this geometry can be employed to determine the composite charge of the carriers in the FQHE state, we have paid special attention to studies of the coupling between the two counter-propagating edge states in our Corbino geometry. Possibility of tunneling between Luttinger liquid type of states is discussed.
Fig. 1. SEM image of one of our graphene Corbino disk samples; all devices display corrugations, either radially or unidirectionally across the whole disk. The outer diameter of the Corbino disk is 800 nm.
Pertti Hakonen
Low Temperature Laboratory, Department of Applied Physics, Aalto University, Espoo, Finland
We have succeeded in manufacturing high-quality suspended graphene samples in Corbino geometry. The Corbino geometry offers two important advantages when compared with standard quantum Hall bars. First, the longitudinal conductivity results can be directly compared with theory, without any need of a matrix inversion like in the case of Hall bar measurements. Second, it improves the resolution in the transport measurement regime where the longitudinal conductance is very small. These are important factors for our experiments aiming at shot noise mapping of charge carries in the fractional quantum Hall state of graphene.
In addition to electrical conductivity and noise, we have determined fundamental mechanical modes of our monolayer graphene Corbino device. In conductance experiments up to 9T field, we can clearly see the fractional states with filling factors 1/3 and 2/5. The mechanical resonance frequency is employed to yield additional information on the carrier density and dynamics near the integer and fractional QHE levels. In order to find out whether shot noise data in this geometry can be employed to determine the composite charge of the carriers in the FQHE state, we have paid special attention to studies of the coupling between the two counter-propagating edge states in our Corbino geometry. Possibility of tunneling between Luttinger liquid type of states is discussed.
Fig. 1. SEM image of one of our graphene Corbino disk samples; all devices display corrugations, either radially or unidirectionally across the whole disk. The outer diameter of the Corbino disk is 800 nm.
Spectroscopy for the Masses (of Carbon Atoms)
Eric J Heller
Harvard University
When valence and conduction band energies are linear in momentum or nearly so, as in graphene near the K point, qualitatively new things happen to absorption, pulse-probe emission, and Raman spectroscopy. A transition for a photon of fixed frequency “slides” and has amplitude for producing correlated holes and electrons up and down the valence and conduction bands, along with a phonon, all resonant with the photon. Normally the phonon processes are minor compared to elastic absorption and emission, but the inelastic sliding process can overwhelm by sheer numbers of possible transitions. The bright Raman features and other aspects of Raman spectroscopy are thus explained, the excess absorption in the UV is quantitatively explained, and the hot thermal emission after pulsed absorption is shown to be a result of the instantaneous production of phonons and many electron-hole pairs up and down the Dirac cones (forming an exciton), not e-e scattering and relaxation.
Eric J Heller
Harvard University
When valence and conduction band energies are linear in momentum or nearly so, as in graphene near the K point, qualitatively new things happen to absorption, pulse-probe emission, and Raman spectroscopy. A transition for a photon of fixed frequency “slides” and has amplitude for producing correlated holes and electrons up and down the valence and conduction bands, along with a phonon, all resonant with the photon. Normally the phonon processes are minor compared to elastic absorption and emission, but the inelastic sliding process can overwhelm by sheer numbers of possible transitions. The bright Raman features and other aspects of Raman spectroscopy are thus explained, the excess absorption in the UV is quantitatively explained, and the hot thermal emission after pulsed absorption is shown to be a result of the instantaneous production of phonons and many electron-hole pairs up and down the Dirac cones (forming an exciton), not e-e scattering and relaxation.
Chiral Three-Dimensional Photonic Crystals for Controlling Light-Matter Interactions
Satoshi Iwamoto1,2, Shun Takahashi, Takeyoshi Tajiri, Yasutomo Ota2, and Yasuhiko Arakawa1,2
1Institute of Industrial Science, The University of Tokyo
2Institute for Nano Quantum Information Electronics, The University of Tokyo
4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
[email protected]
In photonic crystal (PhC) structures, the electromagnetic vacuum fields are largely modified compared with those in uniform media. This allows to engineer light propagation and light-matter interactions in the structures. Various demonstrations, such as efficient lasing at the photonic bandedge in defect-less PhCs, slow light enhancement of nonlinear optics in PhC waveguides, have been reported. In addition, cavity quantum electrodynamics in PhC nanocavities coupled with semiconductor quantum dots (QDs) has also been explored intensively. However, in most of them, 2D PhC slabs have been used. On the other hand, in 3D PhCs, the third dimension will add new degrees of freedom for controlling photons and light-matter interaction.
In this presentation, we discuss semiconductor-based chiral 3D PhC and its application to controlling the light emission properties of InAs QDs. Our chiral 3D PhC structure is composed of rotationally-stacked 1D gratings and can be fabricated by layer-by-layer techniques. Because of the chiral nature of the structure, we can control the electromagnetic vacuum field for circularly polarized photons in chiral 3D PhCs. As a consequence, the structures exhibit artificial optical activity although they are fabricated by non-chiral materials. We have fabricated GaAs chiral 3D PhCs by using micro-manipulation method and have demonstrated giant optical rotation [1] and broadband circular dichroism [2]. The modified circularly polarized vacuum field also influences the light emission properties of materials located in the environment. We experimentally observed highly-circularly polarized light emission from QDs embedded in a chiral 3D PhC [3]. At the bandedge of a circularly-polarized photonic band, the degree of polarization of emitted photons is enhanced, which reflects the increase of photonic density of stats of circularly polarized photons at the bandedge.
Acknowledgements
This work is supported in part by JSPS KAKENHI Grant-in-Aid for Specially Promoted Research (15H05700), MEXT KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas (15H05868), the Project for Developing Innovation Systems of MEXT, and NEDO project.
References
[1] S. Takahashi, A. Tandaechanurat, R. Igusa, Y. Ota, J. Tatebayashi, S. Iwamoto, and Y. Arakawa, Opt. Express 21, 29905 (2013).
[2] S. Takahashi, T. Tajiri, Y. Ota, J. Tatebayashi, S. Iwamoto, and Y. Arakawa, Appl. Phys. Lett. 105, 051107 (2014).
[3] S. Takahashi, T. Tajiri, Y. Ota, J. Tatebayashi, S. Iwamoto, and Y. Arakawa, CLEO 2015, FF1C.2. San Jose, USA (2015).
Satoshi Iwamoto1,2, Shun Takahashi, Takeyoshi Tajiri, Yasutomo Ota2, and Yasuhiko Arakawa1,2
1Institute of Industrial Science, The University of Tokyo
2Institute for Nano Quantum Information Electronics, The University of Tokyo
4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
[email protected]
In photonic crystal (PhC) structures, the electromagnetic vacuum fields are largely modified compared with those in uniform media. This allows to engineer light propagation and light-matter interactions in the structures. Various demonstrations, such as efficient lasing at the photonic bandedge in defect-less PhCs, slow light enhancement of nonlinear optics in PhC waveguides, have been reported. In addition, cavity quantum electrodynamics in PhC nanocavities coupled with semiconductor quantum dots (QDs) has also been explored intensively. However, in most of them, 2D PhC slabs have been used. On the other hand, in 3D PhCs, the third dimension will add new degrees of freedom for controlling photons and light-matter interaction.
In this presentation, we discuss semiconductor-based chiral 3D PhC and its application to controlling the light emission properties of InAs QDs. Our chiral 3D PhC structure is composed of rotationally-stacked 1D gratings and can be fabricated by layer-by-layer techniques. Because of the chiral nature of the structure, we can control the electromagnetic vacuum field for circularly polarized photons in chiral 3D PhCs. As a consequence, the structures exhibit artificial optical activity although they are fabricated by non-chiral materials. We have fabricated GaAs chiral 3D PhCs by using micro-manipulation method and have demonstrated giant optical rotation [1] and broadband circular dichroism [2]. The modified circularly polarized vacuum field also influences the light emission properties of materials located in the environment. We experimentally observed highly-circularly polarized light emission from QDs embedded in a chiral 3D PhC [3]. At the bandedge of a circularly-polarized photonic band, the degree of polarization of emitted photons is enhanced, which reflects the increase of photonic density of stats of circularly polarized photons at the bandedge.
Acknowledgements
This work is supported in part by JSPS KAKENHI Grant-in-Aid for Specially Promoted Research (15H05700), MEXT KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas (15H05868), the Project for Developing Innovation Systems of MEXT, and NEDO project.
References
[1] S. Takahashi, A. Tandaechanurat, R. Igusa, Y. Ota, J. Tatebayashi, S. Iwamoto, and Y. Arakawa, Opt. Express 21, 29905 (2013).
[2] S. Takahashi, T. Tajiri, Y. Ota, J. Tatebayashi, S. Iwamoto, and Y. Arakawa, Appl. Phys. Lett. 105, 051107 (2014).
[3] S. Takahashi, T. Tajiri, Y. Ota, J. Tatebayashi, S. Iwamoto, and Y. Arakawa, CLEO 2015, FF1C.2. San Jose, USA (2015).
Nanoscale Magnetic Imaging of Condensed Matter Systems using Diamond Spins
Ania Bleszynski Jayich
University of California Santa Barbara
The nitrogen vacancy (NV) center in diamond, an emerging quantum technology, is an atom-sized defect in diamond that is a remarkably good sensor of magnetic fields on the nanoscale. In this talk, I describe a novel, state-of-the-art magnetic imaging tool we have developed: we use a single NV spin sensor at the tip of a diamond scanning probe cantilever to image magnetic fields with nanoscale spatial resolution (6 nm) and high sensitivity (3 mT/Hz1/2) at cryogenic temperatures. We have applied this tool to image vortices in an iron pnictide superconductor as well as topological defects in skyrmion-hosting systems.
Ania Bleszynski Jayich
University of California Santa Barbara
The nitrogen vacancy (NV) center in diamond, an emerging quantum technology, is an atom-sized defect in diamond that is a remarkably good sensor of magnetic fields on the nanoscale. In this talk, I describe a novel, state-of-the-art magnetic imaging tool we have developed: we use a single NV spin sensor at the tip of a diamond scanning probe cantilever to image magnetic fields with nanoscale spatial resolution (6 nm) and high sensitivity (3 mT/Hz1/2) at cryogenic temperatures. We have applied this tool to image vortices in an iron pnictide superconductor as well as topological defects in skyrmion-hosting systems.
Spin Orbit Interaction in III-V Semiconductor 2DEG and Layered Semiconductor GaSe
Makoto Kohda
Department of Materials Science, Tohoku University, 980-8579 Sendai, Japan
Electron spins have been hailed as a novel degree of freedom in semiconductors as well as quantum materials such as atomic layer materials and topological insulators because utilization of both the electrons’ charge and spin in two dimensional system and edge states expects the realization of fast- and low-power devices in atomic scales. In order to control spin states in these material systems, spin orbit interaction (SOI) plays an important role. Since the SOI acts as an effective magnetic field for moving electrons, it enables us to realize various spin functionalities without using external magnetic fields and magnetic materials. In III-V semicondcutor quantum wells, since the induced effective magnetic fields are inplane and controlled by the external gate, we have demonstrated spin generation [1], spin manipulation [2] and long spin transport [3-5] by electrical control of SOIs. I will also present the quantum interference effect in layered semiconductor GaSe. Since the GaSe exhibits unique characteristics such as a direct band gap and perpendicular effective magnetic field to the surface, the gate control of SOI in GaSe would be a key for future quantum material devices.
[1] M. Kohda et al., Nat. Commun. 3, 1082 (2012). [2] F. Nagasawa et al., Phys. Rev. Lett. 108, 086801 (2012). [3] M. Kohda et al., Phys. Rev. B 86, 081306(R) (2012). [4] Y. Kunihashi et al., Nat. Commun. 7, 10722 (2016). [5] K. Yoshizumi et al., Appl. Phys. Lett. 108, 132402 (2016).
Makoto Kohda
Department of Materials Science, Tohoku University, 980-8579 Sendai, Japan
Electron spins have been hailed as a novel degree of freedom in semiconductors as well as quantum materials such as atomic layer materials and topological insulators because utilization of both the electrons’ charge and spin in two dimensional system and edge states expects the realization of fast- and low-power devices in atomic scales. In order to control spin states in these material systems, spin orbit interaction (SOI) plays an important role. Since the SOI acts as an effective magnetic field for moving electrons, it enables us to realize various spin functionalities without using external magnetic fields and magnetic materials. In III-V semicondcutor quantum wells, since the induced effective magnetic fields are inplane and controlled by the external gate, we have demonstrated spin generation [1], spin manipulation [2] and long spin transport [3-5] by electrical control of SOIs. I will also present the quantum interference effect in layered semiconductor GaSe. Since the GaSe exhibits unique characteristics such as a direct band gap and perpendicular effective magnetic field to the surface, the gate control of SOI in GaSe would be a key for future quantum material devices.
[1] M. Kohda et al., Nat. Commun. 3, 1082 (2012). [2] F. Nagasawa et al., Phys. Rev. Lett. 108, 086801 (2012). [3] M. Kohda et al., Phys. Rev. B 86, 081306(R) (2012). [4] Y. Kunihashi et al., Nat. Commun. 7, 10722 (2016). [5] K. Yoshizumi et al., Appl. Phys. Lett. 108, 132402 (2016).
Photonic Quantum Computing
Dylan Mahler
University of Bristol
Of the various approaches to quantum computing, photons are appealing for their low-noise properties and ease of manipulation at the single qubit level; while the challenge of entangling interactions between photons can be met via measurement induced non-linearities. However, the real excitement with this architecture is the promise of ultimate manufacturability: All of the components---inc. sources, detectors, filters, switches, delay lines---have been implemented on chip, and increasingly sophisticated integration of these components is being achieved. We will discuss the opportunities and challenges of a fully integrated photonic quantum computer.
Dylan Mahler
University of Bristol
Of the various approaches to quantum computing, photons are appealing for their low-noise properties and ease of manipulation at the single qubit level; while the challenge of entangling interactions between photons can be met via measurement induced non-linearities. However, the real excitement with this architecture is the promise of ultimate manufacturability: All of the components---inc. sources, detectors, filters, switches, delay lines---have been implemented on chip, and increasingly sophisticated integration of these components is being achieved. We will discuss the opportunities and challenges of a fully integrated photonic quantum computer.
Anomalous Hall Effect in High-mobility ZnO Two-dimensional Electron System
Denis Maryenko
RIKEN Center for Emergent Matter Science (CEMS), Japan
Two-dimensional electron system confined at the oxide interface between ZnO and MgZnO emerged in recent years as a fertile platform for studies of many-body effects in low-dimensional electron systems. It is evident, for instance, from the observation of spin-dependent transport in a nominally non-magnetic ZnO structure and from the observation of even-denominator fractional quantum Hall states at Landau level filling factors n=3/2 and 7/2 – the first time observation of the exotic states outside the realm of GaAs [1,2].
In this talk, I will show the clear evidences for the interaction between the mobile electrons and localized magnetic moments, manifested in the observation of the anomalous Hall effect (AHE) [3]. At low temperatures, MgZnO/ZnO heterostructure yields an AHE response similar to that of a clean ferromagnetic metal, while keeping a large anomalous Hall angle. The observation of AHE is consistent with the Giovannini-Kondo model, in which the localized magnetic moments, which are here unpaired electrons localized at the epitaxial point defects, couple with the orbital motion of mobile electrons leading to the skew scattering [4,5].
The presented study reveals a new aspect of many-body interactions in two-dimensional electron system and shows how it can lead to the emergence of AHE in a non-magnetic system. The observation of both even-denominator fractional quantum Hall states and the anomalous Hall effect brings ZnO to the forefront of high-mobility two-dimensional charge carrier systems.
[1] D. Maryenko, J. Falson et al., Phys. Rev. Lett. 115, 197601 (2015)
[2] J. Falson, D. Maryenko et al., Nat. Physics 11, 347 (2015)
[3] D. Maryenko et al., submitted 2016
[4] B. Giovannini, Journal of Low Temperature Physics 11, 489 (1973)
[5] J. Kondo, Progress of Theoretical Physics 27, 772 (1962)
Denis Maryenko
RIKEN Center for Emergent Matter Science (CEMS), Japan
Two-dimensional electron system confined at the oxide interface between ZnO and MgZnO emerged in recent years as a fertile platform for studies of many-body effects in low-dimensional electron systems. It is evident, for instance, from the observation of spin-dependent transport in a nominally non-magnetic ZnO structure and from the observation of even-denominator fractional quantum Hall states at Landau level filling factors n=3/2 and 7/2 – the first time observation of the exotic states outside the realm of GaAs [1,2].
In this talk, I will show the clear evidences for the interaction between the mobile electrons and localized magnetic moments, manifested in the observation of the anomalous Hall effect (AHE) [3]. At low temperatures, MgZnO/ZnO heterostructure yields an AHE response similar to that of a clean ferromagnetic metal, while keeping a large anomalous Hall angle. The observation of AHE is consistent with the Giovannini-Kondo model, in which the localized magnetic moments, which are here unpaired electrons localized at the epitaxial point defects, couple with the orbital motion of mobile electrons leading to the skew scattering [4,5].
The presented study reveals a new aspect of many-body interactions in two-dimensional electron system and shows how it can lead to the emergence of AHE in a non-magnetic system. The observation of both even-denominator fractional quantum Hall states and the anomalous Hall effect brings ZnO to the forefront of high-mobility two-dimensional charge carrier systems.
[1] D. Maryenko, J. Falson et al., Phys. Rev. Lett. 115, 197601 (2015)
[2] J. Falson, D. Maryenko et al., Nat. Physics 11, 347 (2015)
[3] D. Maryenko et al., submitted 2016
[4] B. Giovannini, Journal of Low Temperature Physics 11, 489 (1973)
[5] J. Kondo, Progress of Theoretical Physics 27, 772 (1962)
Ferromagnetism, Quantum Anomalous Hall State and Dissipationless Chiral Conduction in Topological Insulators
Jagadeesh S. Moodera
Physics Department, Francis Bitter Magnet Lab, and Plasma Science and Fusion Center
M. I.T. Cambridge, MA 02139
A topological insulator (TI) with broken time reversal symmetry (TRS) by ferromagnetic perturbation of their Dirac surface states can display many exotic quantum phenomena including the quantum anomalous Hall (QAH) effect and dissipationless quantized Hall transport. The realization of the QAH effect in realistic materials requires ferromagnetic insulating materials that have topologically non-trivial electronic band structures. In a TI, the ferromagnetic order and TRS breaking is achievable through doping with a magnetic element or via ferromagnetic proximity coupling with a magnetic material. Our experimental success by both approaches showed excellent results along with some unanticipated observations: the proximity induced magnetism in TI exhibited stability far above the expected temperature range. We will discuss the robust QAH state and dissipationless chiral edge current flow achieved in the (doped) hard ferromagnetic TI system.1,2 In the proximity approach due to the short range nature of the ferromagnetic exchange interaction, it affects only near the surface of a TI, while leaving its bulk states unaffected. This interfacial ferromagnetism is observed in a variety of bi-layers, providing a possibility to control this phenomenon.3 Our results could be a significant step towards dissipationless transport for electronic applications, making such devices more amenable for metrology and spintronics applications. Furthermore, our study of the gate and temperature dependences of transport measurements may elucidate the causes of the dissipative edge channels and the need for very low temperature to observe QAH.
In collaboration with: At MIT, CuiZu Chang,2,3 Ferhat Katmis, 1.2,3 Peng Wei. 1,2,3; At Penn State U, W-W. Zhao, D. Y. Kim, C-x. Liu, J. K. Jain, M. H. W. Chan; At Oakridge National Lab, V. Lauter; From Northeastern U., B. A. Assaf, M. E. Jamer, D. Heiman; At Argonne Lab, J. W. Freeland; At Saha Institute of Nuclear Physics (India), B. Satpati.
Work supported by NSF Grant DMR-1207469, the ONR Grant N00014-13-1-0301, and the STC Center for Integrated Quantum Materials under NSF grant DMR-1231319.
References:
1. P. Wei et al., Phys. Rev. Lett. 110, 186807 (2013)
2. C. -Z Chang et al., Nat. Matl 13, 473 (2015); Phys. Rev. Lett. 115, 057206 (2015)
3. F. Katmis et al., Nature (to be published, 2016)
Jagadeesh S. Moodera
Physics Department, Francis Bitter Magnet Lab, and Plasma Science and Fusion Center
M. I.T. Cambridge, MA 02139
A topological insulator (TI) with broken time reversal symmetry (TRS) by ferromagnetic perturbation of their Dirac surface states can display many exotic quantum phenomena including the quantum anomalous Hall (QAH) effect and dissipationless quantized Hall transport. The realization of the QAH effect in realistic materials requires ferromagnetic insulating materials that have topologically non-trivial electronic band structures. In a TI, the ferromagnetic order and TRS breaking is achievable through doping with a magnetic element or via ferromagnetic proximity coupling with a magnetic material. Our experimental success by both approaches showed excellent results along with some unanticipated observations: the proximity induced magnetism in TI exhibited stability far above the expected temperature range. We will discuss the robust QAH state and dissipationless chiral edge current flow achieved in the (doped) hard ferromagnetic TI system.1,2 In the proximity approach due to the short range nature of the ferromagnetic exchange interaction, it affects only near the surface of a TI, while leaving its bulk states unaffected. This interfacial ferromagnetism is observed in a variety of bi-layers, providing a possibility to control this phenomenon.3 Our results could be a significant step towards dissipationless transport for electronic applications, making such devices more amenable for metrology and spintronics applications. Furthermore, our study of the gate and temperature dependences of transport measurements may elucidate the causes of the dissipative edge channels and the need for very low temperature to observe QAH.
In collaboration with: At MIT, CuiZu Chang,2,3 Ferhat Katmis, 1.2,3 Peng Wei. 1,2,3; At Penn State U, W-W. Zhao, D. Y. Kim, C-x. Liu, J. K. Jain, M. H. W. Chan; At Oakridge National Lab, V. Lauter; From Northeastern U., B. A. Assaf, M. E. Jamer, D. Heiman; At Argonne Lab, J. W. Freeland; At Saha Institute of Nuclear Physics (India), B. Satpati.
Work supported by NSF Grant DMR-1207469, the ONR Grant N00014-13-1-0301, and the STC Center for Integrated Quantum Materials under NSF grant DMR-1231319.
References:
1. P. Wei et al., Phys. Rev. Lett. 110, 186807 (2013)
2. C. -Z Chang et al., Nat. Matl 13, 473 (2015); Phys. Rev. Lett. 115, 057206 (2015)
3. F. Katmis et al., Nature (to be published, 2016)
Nonlinear and Nonreciprocal Responses of Topological Matters
Naoto Nagaosa
Center for Emergent Matter Science (CEMS) and Department of Applied Physics, The University of Tokyo
Topological aspects of the electronic states in solids have attracted recent intensive attention. The basic idea is that the manifold in the Hilbert space constituted by the low energy eigenstates often has nontrivial quantum geometry. Therefore, the applications of this concept have been restricted to the ground state and low energy phenomena. In this talk, I will talk about the possible generalization of this idea to the nonlinear and nonequilibrium states. In this case, the transitions between the two manifolds in Hilbert space play the key role. As a representative example, the shift current in noncentrosymmetric systems will be discussed.
This work has been done in collaboration with T. Morimoto.
Naoto Nagaosa
Center for Emergent Matter Science (CEMS) and Department of Applied Physics, The University of Tokyo
Topological aspects of the electronic states in solids have attracted recent intensive attention. The basic idea is that the manifold in the Hilbert space constituted by the low energy eigenstates often has nontrivial quantum geometry. Therefore, the applications of this concept have been restricted to the ground state and low energy phenomena. In this talk, I will talk about the possible generalization of this idea to the nonlinear and nonequilibrium states. In this case, the transitions between the two manifolds in Hilbert space play the key role. As a representative example, the shift current in noncentrosymmetric systems will be discussed.
This work has been done in collaboration with T. Morimoto.
Nanoscale Devices to Examine Correlated Materials
Douglas Natelson
Department of Physics and Astronomy, Rice University, Houston, TX 77005
Enormous progress in quantum materials, particularly metals and semiconductors, has been enabled through the development and application of nanofabrication techniques. Nanoscale devices have permitted the study of electronic properties of these systems on physically significant length scales, and confinement and control of individual electrons. Applying these techniques to correlated materials has lagged behind, however, in part because of the complex and stoichiometry-sensitive nature of these systems. I will discuss three sets of experiments that we have performed using micro/nanoscale structures based on strongly correlated materials: magnetotransport in the layered antiferromagnet V5S8 down to the nanometer thickness regime (collaboration with Prof. Jun Lou of Rice University); mesoscale transport in a bad metal, hydrogen-doped VO2, as well as oxide quantum wells (collaborations with Prof. Darrell Schlom of Cornell and Prof. Susanne Stemmer of UCSB, respectively); and preliminary measurements on shot noise in tunnel junctions fabricated in YBCO (collaboration with Dr. Shane Cybart and Prof. R. Dynes at UCSD). These experiments look at the role of reduced dimensionality in magnetic ordering, and the nature of low energy charge-carrying excitations in systems where the existence of well-defined conventional quasiparticles is uncertain.
Douglas Natelson
Department of Physics and Astronomy, Rice University, Houston, TX 77005
Enormous progress in quantum materials, particularly metals and semiconductors, has been enabled through the development and application of nanofabrication techniques. Nanoscale devices have permitted the study of electronic properties of these systems on physically significant length scales, and confinement and control of individual electrons. Applying these techniques to correlated materials has lagged behind, however, in part because of the complex and stoichiometry-sensitive nature of these systems. I will discuss three sets of experiments that we have performed using micro/nanoscale structures based on strongly correlated materials: magnetotransport in the layered antiferromagnet V5S8 down to the nanometer thickness regime (collaboration with Prof. Jun Lou of Rice University); mesoscale transport in a bad metal, hydrogen-doped VO2, as well as oxide quantum wells (collaborations with Prof. Darrell Schlom of Cornell and Prof. Susanne Stemmer of UCSB, respectively); and preliminary measurements on shot noise in tunnel junctions fabricated in YBCO (collaboration with Dr. Shane Cybart and Prof. R. Dynes at UCSD). These experiments look at the role of reduced dimensionality in magnetic ordering, and the nature of low energy charge-carrying excitations in systems where the existence of well-defined conventional quasiparticles is uncertain.
Excitonic Optomechanics in a GaAs System
Hajime Okamoto1, Takayuki Watanabe1,2, Ryuichi Ohta1, Koji Onomitsu1, Hideki Gotoh1, Tetsuomi Sogawa1, and Hiroshi Yamaguchi1,2,
1NTT Basic Research Laboratories, 2Tohoku University
Optical control of micro/nano-mechanical resonators has been widely demonstrated via cavity-enhanced radiation pressure or photothermal backaction [1,2]. Such cavity optomechanics allow highly tunable manipulation of a mechanical (phonon) resonator by photons. However, it cannot be straightforwardly extended to integrated mechanical systems because it needs delicate cavity operation, including tapered-fiber access and coupling adjustment. Thus, an alternative cavity-free approach is highly demanded in order to practically apply the optical control capability to integrated micro/nano-mechanical systems, such as mechanical circuits and sensor arrays. In this talk, we present cavity-free optomechanical coupling in a GaAs microcantilever system, which is induced by excitonic transitions through opto-piezoelectric backaction [3,4]. The opto-piezoelectric backaction from the bound electron-hole pairs, i.e. excitons, enables us to probe the optical transition simply with a sub-nanowatt power of light [4] and thereby realize high-sensitivity optomechanical spectroscopy. Detuning the photon energy from the exciton resonance results in self-feedback cooling and amplification of the thermomechanical motion [4], which is in a manner similar to the conventional cavity optomechanics. This cavity-free optomechanical coupling enables highly tunable and addressable control of micro/nano-mechanical resonators, allowing high-speed programmable manipulation of mechanical devices and sensor arrays.
[1] M. Aspelmeyer, T. J. Kippenberg and F. Marquardt, Rev. Mod. Phys. 86, 1391-1452 (2014).
[2] I. Favero and K. Karrai, Nature Photon. 3, 201-205 (2009).
[3] H. Okamoto et al., Phys. Rev. Lett. 106, 036801 (2011).
[4] H. Okamoto et al., Nature Commun. 6, 8478 (2015).
Hajime Okamoto1, Takayuki Watanabe1,2, Ryuichi Ohta1, Koji Onomitsu1, Hideki Gotoh1, Tetsuomi Sogawa1, and Hiroshi Yamaguchi1,2,
1NTT Basic Research Laboratories, 2Tohoku University
Optical control of micro/nano-mechanical resonators has been widely demonstrated via cavity-enhanced radiation pressure or photothermal backaction [1,2]. Such cavity optomechanics allow highly tunable manipulation of a mechanical (phonon) resonator by photons. However, it cannot be straightforwardly extended to integrated mechanical systems because it needs delicate cavity operation, including tapered-fiber access and coupling adjustment. Thus, an alternative cavity-free approach is highly demanded in order to practically apply the optical control capability to integrated micro/nano-mechanical systems, such as mechanical circuits and sensor arrays. In this talk, we present cavity-free optomechanical coupling in a GaAs microcantilever system, which is induced by excitonic transitions through opto-piezoelectric backaction [3,4]. The opto-piezoelectric backaction from the bound electron-hole pairs, i.e. excitons, enables us to probe the optical transition simply with a sub-nanowatt power of light [4] and thereby realize high-sensitivity optomechanical spectroscopy. Detuning the photon energy from the exciton resonance results in self-feedback cooling and amplification of the thermomechanical motion [4], which is in a manner similar to the conventional cavity optomechanics. This cavity-free optomechanical coupling enables highly tunable and addressable control of micro/nano-mechanical resonators, allowing high-speed programmable manipulation of mechanical devices and sensor arrays.
[1] M. Aspelmeyer, T. J. Kippenberg and F. Marquardt, Rev. Mod. Phys. 86, 1391-1452 (2014).
[2] I. Favero and K. Karrai, Nature Photon. 3, 201-205 (2009).
[3] H. Okamoto et al., Phys. Rev. Lett. 106, 036801 (2011).
[4] H. Okamoto et al., Nature Commun. 6, 8478 (2015).
Quantum Photonics with Single-Electron Devices
Jason Petta
Princeton University, Department of Physics
Isotopically enriched silicon has been termed a “semiconductor vacuum” due to its ability to support very long quantum coherence times. I will describe recent efforts by my group to couple a single electron trapped in a Si/SiGe double quantum dot to the photonic field of a superconducting coplanar waveguide resonator. A high degree of control over a single electron wavefunction is achieved using a recently developed overlapping aluminum gate electrode architecture. Measurements of the microwave transmission through the superconducting resonator allow sensitive measurements of the charge state occupation of the Si/SiGe double quantum dot.
Jason Petta
Princeton University, Department of Physics
Isotopically enriched silicon has been termed a “semiconductor vacuum” due to its ability to support very long quantum coherence times. I will describe recent efforts by my group to couple a single electron trapped in a Si/SiGe double quantum dot to the photonic field of a superconducting coplanar waveguide resonator. A high degree of control over a single electron wavefunction is achieved using a recently developed overlapping aluminum gate electrode architecture. Measurements of the microwave transmission through the superconducting resonator allow sensitive measurements of the charge state occupation of the Si/SiGe double quantum dot.
Novel Quantum Materials Beyond Graphene: Germanene Nanoflakes
Dr. Steven L. Richardson
Department of Electrical and Computer Engineering, and National Science Foundation (NSF) Center for Integrated Quantum Materials
College of Engineering, Architecture, and Computer Sciences, Howard University, Washington, DC, USA
While graphene has remarkable transport properties, it does not possess a band gap and thus has limited applications in device physics. It is therefore important to both identify and study new two-dimensional atomically thin quantum materials beyond graphene. Germanene, the germanium analog of graphene, is one such example of a new quantum material. The large spin-orbit coupling present in germanium alters its electronic structure to produce novel transport and optoelectronic properties than are not seen in graphene.
Recently, there has been some progress in the synthesis of thin films of germanene and germanane, the hydrogenated form of germanene, using both top-down processes like molecular beam epitaxy and chemical vapor phase deposition and a bottom-up process such as direct chemical synthesis. We would like to suggest an additional approach to the bottom-up process by using germanium nanoflakes to serve as molecular seeds or precursors for the large-scale growth of pure sheets of germanene in chemical vapor phase deposition experiments.
To help guide future experimental work in how germanene nanoflakes might be used to grow large-scale films of germanene, we have used density-functional theory to calculate the electronic, structural, vibrational, and optical properties of several lower-order germanene nanoflakes such as hexagermabenzene (Ge6H6), germa-naphthalene (Ge10H8), germa-anthracene (Ge14H10), germa-phenanthrene (Ge14H10), and germa-pyrene (Ge16H10). We have determined that these nanoflakes are thermodynamically stable with a geometry that is buckled due to pseudo-Jahn Teller distortions from the planar forms that are present in graphene nanoflakes. In addition, we have computed accurate infrared and Raman spectra for a family of selected germanene nanoflakes. Our first-principles studies on the properties of germanene nanoflakes will be critical for characterizing these molecules in future experimental efforts.
Dr. Steven L. Richardson
Department of Electrical and Computer Engineering, and National Science Foundation (NSF) Center for Integrated Quantum Materials
College of Engineering, Architecture, and Computer Sciences, Howard University, Washington, DC, USA
While graphene has remarkable transport properties, it does not possess a band gap and thus has limited applications in device physics. It is therefore important to both identify and study new two-dimensional atomically thin quantum materials beyond graphene. Germanene, the germanium analog of graphene, is one such example of a new quantum material. The large spin-orbit coupling present in germanium alters its electronic structure to produce novel transport and optoelectronic properties than are not seen in graphene.
Recently, there has been some progress in the synthesis of thin films of germanene and germanane, the hydrogenated form of germanene, using both top-down processes like molecular beam epitaxy and chemical vapor phase deposition and a bottom-up process such as direct chemical synthesis. We would like to suggest an additional approach to the bottom-up process by using germanium nanoflakes to serve as molecular seeds or precursors for the large-scale growth of pure sheets of germanene in chemical vapor phase deposition experiments.
To help guide future experimental work in how germanene nanoflakes might be used to grow large-scale films of germanene, we have used density-functional theory to calculate the electronic, structural, vibrational, and optical properties of several lower-order germanene nanoflakes such as hexagermabenzene (Ge6H6), germa-naphthalene (Ge10H8), germa-anthracene (Ge14H10), germa-phenanthrene (Ge14H10), and germa-pyrene (Ge16H10). We have determined that these nanoflakes are thermodynamically stable with a geometry that is buckled due to pseudo-Jahn Teller distortions from the planar forms that are present in graphene nanoflakes. In addition, we have computed accurate infrared and Raman spectra for a family of selected germanene nanoflakes. Our first-principles studies on the properties of germanene nanoflakes will be critical for characterizing these molecules in future experimental efforts.
Nanoscale Magnetic Imaging using Single Spins in Diamond
Brendan J. Shields
Department of Physics, University of Basel
The nitrogen-vacancy (NV) center in diamond has emerged as an exceptional system for a variety of sensing applications in areas ranging from mesoscopic physics to materials science and biology. A single electronic spin localized to the NV defect is sensitive to physical quantities such as magnetic and electric fields, pressure, and temperature, and offers potentially atomic-scale spatial resolution with stable, robust operation over a wide temperature range. Our work focuses on magnetic imaging with an NV center embedded in a diamond AFM probe, which enables quantitative imaging of magnetic fields with a spatial resolution of tens of nanometers. I will present recent results in two materials systems: antiferromagnetic domains in Cr2O3 films, and vortices in the superconductor YBa2Cu3O7-δ.
Brendan J. Shields
Department of Physics, University of Basel
The nitrogen-vacancy (NV) center in diamond has emerged as an exceptional system for a variety of sensing applications in areas ranging from mesoscopic physics to materials science and biology. A single electronic spin localized to the NV defect is sensitive to physical quantities such as magnetic and electric fields, pressure, and temperature, and offers potentially atomic-scale spatial resolution with stable, robust operation over a wide temperature range. Our work focuses on magnetic imaging with an NV center embedded in a diamond AFM probe, which enables quantitative imaging of magnetic fields with a spatial resolution of tens of nanometers. I will present recent results in two materials systems: antiferromagnetic domains in Cr2O3 films, and vortices in the superconductor YBa2Cu3O7-δ.
Magnetoelectric Responses from Superstructures of Topological Insulators
Yoshinori Tokura a,b
a RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
b Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
Superstrcutres composed of magnetic and non-magnetic topological insulators (TIs) have been designed and fabiricated to stabilize the quantum anomalous Hall states and the hybrid quantum normal and anomalous Hall states with (ν=0 and ±1) at higher temperatures. We report on the emergent magetnetoelctric responses observed in these TI superstructures, including skyrmion formation, zero-biase photocurrent, topological Faraday and Kerr roations, and possible Axion insulator.
This work was done in collaboration with R. Yoshimi, K.N. Okada, K. Yasuda, M. Mogi, N. Ogawa, Y. Takahasi, M. Kawamura, K.S. Takahashi, A. Tsukazaki, R. Wakatsuki, T. Morimoto, M. Kawasaki, and N. Nagaosa.
Yoshinori Tokura a,b
a RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
b Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
Superstrcutres composed of magnetic and non-magnetic topological insulators (TIs) have been designed and fabiricated to stabilize the quantum anomalous Hall states and the hybrid quantum normal and anomalous Hall states with (ν=0 and ±1) at higher temperatures. We report on the emergent magetnetoelctric responses observed in these TI superstructures, including skyrmion formation, zero-biase photocurrent, topological Faraday and Kerr roations, and possible Axion insulator.
This work was done in collaboration with R. Yoshimi, K.N. Okada, K. Yasuda, M. Mogi, N. Ogawa, Y. Takahasi, M. Kawamura, K.S. Takahashi, A. Tsukazaki, R. Wakatsuki, T. Morimoto, M. Kawasaki, and N. Nagaosa.
Search Directions and Smoking Gun Signatures of Weyl Fermions
Ashvin Vishwanath
Harvard University/UC Berkeley
I will discuss unique physical properties of Weyl fermions, including quantum oscillations from Fermi arc surface states and physical properties controlled by the chiral anomaly. I will also discuss our recent efforts towards a directed search for materials exhibiting Weyl and Dirac nodes, utilizing constraints imposed on the band structure by electron filling.
Ashvin Vishwanath
Harvard University/UC Berkeley
I will discuss unique physical properties of Weyl fermions, including quantum oscillations from Fermi arc surface states and physical properties controlled by the chiral anomaly. I will also discuss our recent efforts towards a directed search for materials exhibiting Weyl and Dirac nodes, utilizing constraints imposed on the band structure by electron filling.
Cultivating Next Generation Nanoscience: The Center for Nanoscale Systems at Harvard University
William L. Wilson
Center for Nanoscale Systems, Faculty of Arts and Sciences, Harvard University, 11 Oxford Street, Cambridge, MA 02138, USA
The Center for Nanoscale Systems (CNS) at Harvard University has rapidly advanced as an important national nanotechnology resource. This “open” center has developed a diverse, versatile, array of tools, and instrumentation that enable world-class scientific work ranging from nanoscale electronics, photonics and plasmonics, to studies of advanced Systems Biology, and the development of biomedical systems and devices. As the New England node of the National Nanotechnology Coordinated Infrastructure (NNCI), CNS is one of the most heavily used nanofabrication and imaging facilities in the world. With more than 1600 users, CNS forms an extremely synergistic nanotechnology ecosystem. With its large, diverse user base, well-established user infrastructure, characterization tools, and advanced processing protocols, CNS is positioned as a strong leader driving world-class nanoscience, nanoengineering, as well as exploring new characterization paradigms. For example, scanning probe spectral techniques are poised to play an important role in the development and study of next generation nanomaterials and nano-devices. In particular, Multimodal Atomic Force Microscopy – where the excitation and detection of two flexural eigenmodes of a cantilever with the output signal of the first mode used to image the topography of the surface and the output signal of the second mode used to measure changes in tip-sample interactions - has allowed exquisite nanoscale (10nm), monitoring of the mechanical, magnetic, electrical, and optical properties of systems, in essence detecting materials responses as pN forces at the cantilever. These new probes offer important new insights into complex nanoscale materials and devices. In this talk we will briefly review the activities and wide ranging capabilities of CNS. In addition, we will explore new experimental resources being developed at CNS using scanning probes to explore spectral and dielectric behavior at the nanoscale.
William L. Wilson
Center for Nanoscale Systems, Faculty of Arts and Sciences, Harvard University, 11 Oxford Street, Cambridge, MA 02138, USA
The Center for Nanoscale Systems (CNS) at Harvard University has rapidly advanced as an important national nanotechnology resource. This “open” center has developed a diverse, versatile, array of tools, and instrumentation that enable world-class scientific work ranging from nanoscale electronics, photonics and plasmonics, to studies of advanced Systems Biology, and the development of biomedical systems and devices. As the New England node of the National Nanotechnology Coordinated Infrastructure (NNCI), CNS is one of the most heavily used nanofabrication and imaging facilities in the world. With more than 1600 users, CNS forms an extremely synergistic nanotechnology ecosystem. With its large, diverse user base, well-established user infrastructure, characterization tools, and advanced processing protocols, CNS is positioned as a strong leader driving world-class nanoscience, nanoengineering, as well as exploring new characterization paradigms. For example, scanning probe spectral techniques are poised to play an important role in the development and study of next generation nanomaterials and nano-devices. In particular, Multimodal Atomic Force Microscopy – where the excitation and detection of two flexural eigenmodes of a cantilever with the output signal of the first mode used to image the topography of the surface and the output signal of the second mode used to measure changes in tip-sample interactions - has allowed exquisite nanoscale (10nm), monitoring of the mechanical, magnetic, electrical, and optical properties of systems, in essence detecting materials responses as pN forces at the cantilever. These new probes offer important new insights into complex nanoscale materials and devices. In this talk we will briefly review the activities and wide ranging capabilities of CNS. In addition, we will explore new experimental resources being developed at CNS using scanning probes to explore spectral and dielectric behavior at the nanoscale.
Spotting the Elusive Majorana Under the Microscope
Ali Yazdani
Princeton University
Topological superconductors are a distinct form of matter that is predicted to host boundary Majorana fermions. The search for Majorana quasi-particles in condensed matter systems is motivated in part by their potential use as topological qubits to perform fault-tolerant computation aided by their non-Abelian characteristics. Recently, we have proposed a new platform for the realization of Majorana fermions in condensed matter, based on chains of magnetic atoms on the surface of a superconductor. This platform lends itself to measurements with the scanning tunneling microscope (STM) that can be used to directly visualize the Majorana edge modes with both high energy and spatial resolution. Using rather unique STM instrumentation, we have succeeded in creating this platform and have observed the predicted signatures of localized Majorana edge modes. I will describe our Majorana platform, the experiments to date, and the outlook for further experiments on Majorana fermions in our platform.
Ali Yazdani
Princeton University
Topological superconductors are a distinct form of matter that is predicted to host boundary Majorana fermions. The search for Majorana quasi-particles in condensed matter systems is motivated in part by their potential use as topological qubits to perform fault-tolerant computation aided by their non-Abelian characteristics. Recently, we have proposed a new platform for the realization of Majorana fermions in condensed matter, based on chains of magnetic atoms on the surface of a superconductor. This platform lends itself to measurements with the scanning tunneling microscope (STM) that can be used to directly visualize the Majorana edge modes with both high energy and spatial resolution. Using rather unique STM instrumentation, we have succeeded in creating this platform and have observed the predicted signatures of localized Majorana edge modes. I will describe our Majorana platform, the experiments to date, and the outlook for further experiments on Majorana fermions in our platform.
