Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M62: Electron Transport in Nanostructures IIFocus
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Sponsoring Units: DMP Chair: Xuan Gao, Case Western Reserve University Room: Mile High Ballroom 4C |
Wednesday, March 4, 2020 11:15AM - 11:51AM |
M62.00001: The Observation of Majorana Zero Mode and Conductance Plateau in an Iron-based Superconductor Invited Speaker: Hongjun Gao Majorana zero-modes (MZMs) are spatially-localized zero-energy fractional quasiparticles with non- |
Wednesday, March 4, 2020 11:51AM - 12:03PM |
M62.00002: Excited State Imaging and STM Characterization of Nanomaterials Alison Wallum, Duc Nguyen, Huy Nguyen, Sikai Wu, Iain Carpenter, John Badding, Joseph W Lyding, Martin Gruebele In an effort to spatially resolve excited state properties of nanomaterials with sub-nm resolution, our group has developed an excited state imaging technique known as single-molecule absorption scanning tunneling microscopy (SMA-STM). This technique allows us to probe changes in tunneling associated with laser excitation, creating an image that maps the excited state electronic structure of nanomaterials. We have applied this technique widely to study excited state properties of quantum dots (QDs) and carbon nanotubes (CNTs) and will discuss results surrounding the interaction of optically excited QDs with CNTs. Our results show a distant-dependent transverse polarization of CNTs in the presence of an excited QD, while semiquantitative tight-binding calculations performed on an analogous system allow us to model the observed interaction. We will also discuss our preliminary work with traditional STM on carbon nanothreads and their variants, which aims to characterize the ground state electronic properties of these carbon materials. Initial results show highly variable band gaps of aggregate structures likely due to varied ordering and defects, while techniques allowing for investigation of individual threads will ultimately position us for excited state characterization. |
Wednesday, March 4, 2020 12:03PM - 12:15PM |
M62.00003: Single Molecule Quantum Transport in the Presence of Built-in Electric Fields - a Design Principle? Oliver Monti, Jeffrey Ivie, Nathan Bamberger, Dylan M Dyer Controlling transport in single molecules remains a major challenge, in part due to the difficulties of predicting the electronic structure of a molecule when supported in a metallic nanostructure. Here we discuss the possibility of using molecular dipole moments as built-in electric fields in single molecules to shift the energy level alignment and therefore tailor quantum transport. On the basis of advanced statistical analysis of experimental data from a set of model molecules, we are able to differentiate even rather small differences in the conductance, which enables us to investigate whether built-in electric fields are a useful approach to tailor the interfacial electronic structure in single molecule junctions. |
Wednesday, March 4, 2020 12:15PM - 12:27PM |
M62.00004: Giant Thermopower in Quasi-One-Dimensional LaAlO3/SrTiO3 Quantum Wires Puqing Jiang, Yuhe Tang, Hyungwoo Lee, Jung-Woo Lee, Chang-Beom Eom, Patrick Irvin, Jeremy Levy SrTiO3-based heterointerfaces possess new effects ranging from superconductivity to magnetism. In particular, the two-dimensional (2D) LaAlO3/SrTiO3 interface was previously shown to have highly enhanced and oscillating thermopower when back-gated close to the insulating state [1]. Here we investigated the electrical and thermoelectric transport properties of quasi-one-dimensional (1D) LaAlO3/SrTiO3 quantum wires [2] at a low temperature of 80 mK. We find significantly enhanced and oscillating thermopower for the quantum wires, with values that are comparable to reports for 2D LaAlO3/SrTiO3 [1]. The Mott relation, which governs the diffusive thermopower of non-interacting electrons, works surprisingly well despite the highly ballistic nature of electron transport and evidence of electron-electron interaction in these quantum wires. Our results suggest that the highly enhanced thermopower in 2D SrTiO3-based systems may originate from naturally formed quasi-1D channels at the heterointerfaces. |
Wednesday, March 4, 2020 12:27PM - 12:39PM |
M62.00005: Effects of writing parameters on electron transport in sketched single-electron transistors Philip Shenk, John Maier, Yang Hu, Hyungwoo Lee, Jung-Woo Lee, Chang-Beom Eom, Patrick Irvin, Jeremy Levy Fabrication of single-electron transistors (SETs) and other mesoscopic devices typically requires elaborate nanofabrication techniques. We approach this challenge using a reversible conductive-AFM lithography technique that can locally control the conductivity of the LaAlO3/SrTiO3 interface. We characterize the properties of “sketched” nanostructures as a function of experimentally controllable variables such as writing parameters, back-gate voltage, temperature and magnetic field. Here we focus on the SketchSET geometry [1] which shows discrete addition energies that we can track as a function of source-drain bias and magnetic field. Our findings yield insights into intrinsic interactions between electrons confined within the SET islands. |
Wednesday, March 4, 2020 12:39PM - 12:51PM |
M62.00006: Controling Nonlinear Thermoelectricity of a Quantum Dot by Quantum Interference Nobuhiko Taniguchi We theoretically study how one can control and enhance nanoscale nonlinear thermoelectricity by regulating quantum interference. We take the configuration of a quantum-dot interferometer (a quantum dot embedded in the ring geometry), which can also represent a model of a single-molecule junction. One can adjust quantum coherence by modifying direct conducting channels between the leads (Fano's effect). Within the linear response theory, such Fano resonances have been suggested to enhance drastically the thermoelectric figure of merit, which reaches an order-of-unity value even for a non-thermoelectric material. We revisit the idea by examining the efficiency and the output power in the nonlinear response regime. Based on the microscopic model and nonequilibrium Green function techniques, we can incorporate the strong correlation on the dot and charge-blocking effect. We show how the presence of direct conducting channels can greatly enhance nonlinear thermoelectric performance, even when the resonance width is much larger than temperature. |
Wednesday, March 4, 2020 12:51PM - 1:03PM |
M62.00007: Bell-state correlation in electric currents through lead electrodes connected to a quantum dot Rui Sakano, Akira Oguri, Mikio Eto We study quantum entanglement that is excited in currents through lead electrodes connected to a quantum dot. To assess the emerging entanglement among the lead electrode, we use Bell’s inequality with cross-correlations of current fluctuations [1]. The correlations of the current fluctuations are calculated by using the Anderson impurity model and Green's function in the Keldysh formalism. Electron-hole pairs are induced between two electric leads. |
Wednesday, March 4, 2020 1:03PM - 1:15PM |
M62.00008: Coherent Refraction Across Atomically-Precise Molecular Graphene Junctions Morgan Brubaker, Yi-Ting Chen, Beatriz Sarah Yankelevich, Alison Day, Hari C. Manoharan The construction of functional nanoscopic devices requires an in-depth understanding of electronic transport across interfaces. Electrons in graphene exhibit lightlike behavior due to their massless dispersion relation near the Dirac points; this suggests the ability to construct nanostructures that control electrons analogously to how optical devices such as lenses control light, provided that transport at the interface is understood. Molecular graphene, assembled with atomic manipulation of individual molecules in a low-temperature, ultra-high-vacuum scanning tunneling microscope so as to confine itinerant two-dimensional electrons to a honeycomb lattice, serves as a new tunable form of graphene that features atomically-precise edges and is thus ideal for probing interface transport. We report experiments that use quasiparticle interference measurements to probe the behavior of Dirac electrons incident upon junctions between molecular graphene and a nearly-free two-dimensional electron gas, and between differently-doped regions of molecular graphene. Our results indicate that Dirac electrons are refracted coherently across the junction, analogous to light bending across an interface between two media with mismatched indices of refraction. |
Wednesday, March 4, 2020 1:15PM - 1:27PM |
M62.00009: Persistent Coulomb Blockade Across the Metal-Insulator Transition in Nanoparticle Solids Davis Unruh, Chase Hansen, Alberto Camjayi, Joel Bobadilla, Marcelo J Rozenberg, Gergely T Zimanyi Nanoparticle (NP) solids in opto-electronic and photovoltaic applications have disadvantageously low carrier mobilities. The mobility is suppressed by the disorder driving the NP solids insulators. A Filling-Controlled (FC) Coulomb blockade further suppresses transport at integer fillings. Transport at non-integer fillings can be improved by driving NP solids across a Disorder-Controlled Metal-Insulator Transition (DC-MIT) into their Metallic Phase by enhancing the kinetic energy to overcome the disorder and thus delocalizing the electron wavefunctions. However, the evolution of the FC-Coulomb blockade at integer fillings across the DC-MIT has not been analyzed yet, leaving the question open whether the FC-Coulomb blockade dissolves or persists in some form as the electron wavefunctions delocalize when the DC-MIT is crossed. The work reported here explores this question of how the FC-Coulomb blockade evolves across the DC-MIT by analyzing transport in the Insulating Phase by our Hierarchical Nanoparticle Transport Simulator, and in the Metallic Phase by Dynamical Mean-Field Theory. Remarkably, the FC-Coulomb blockade is found to persist across the DC-MIT. |
Wednesday, March 4, 2020 1:27PM - 1:39PM |
M62.00010: Theoretical Design of Topological Heteronanotubes Chen Hu, Vincent Michaud-Rioux, Wang Yao, Hong Guo We propose and investigate the idea of topological heteronanotubes (THTs) for realizing a one-dimensional (1D) topological material platform that can pave the way to low-power carbon nanoelectronics at room temperature. We predict that the coaxial double-wall heteronanotube, a carbon nanotube (CNT) inside a boron nitride nanotube (BNNT), can act as a THT. Dissipationless topological conducting pathways on the THT are protected by a valley-dependent topological invariance that originates from local topological phase transitions of the CNT modulated by the CNT-BNNT interaction. Spiral THTs, where topological current flows spirally around the tube, function as nanoscale solenoids to induce remarkable magnetic fields due to the dense moire nanopatterning. |
Wednesday, March 4, 2020 1:39PM - 1:51PM |
M62.00011: Towards quantum criticality in Al/InAs Kondo systems Praveen Sriram, Connie Hsueh, Asbjorn Drachmann, Candice Thomas, Geoffrey C. Gardner, Tiantian Wang, Sergei Gronin, Michael Manfra, Charles Marcus, David Goldhaber-Gordon Hybrid metal-semiconductor two-dimensional systems are an attractive platform for exploring correlated electron-electron interactions. Flexible nanopatterning allows design of structures to emulate particular Hamiltonians with electrostatically tunable parameters. Pierre et al. recently demonstrated a quantum phase transition based on a charge Kondo effect[1]. Based in a GaAs heterostructure, the metal was an annealed ohmic contact, requiring much effort to obtain a highly-transparent interface even for a few-micron metal island. InAs may offer significant advantages: pinning of the surface Fermi level in the conduction band allows for direct electrical contact to metals. For example, in-situ epitaxy of aluminum on InAs has resulted in pristine interfaces, leveraged to probe topological superconductivity[2]. Small metallic islands with large charging energies may allow building on earlier charge Kondo work without requiring as low electron temperatures. I will present our initial efforts towards realizing charge Kondo devices on InAs 2DEGs tuned into the quantum Hall regime, with edge states controlled by lithographically defined QPCs. |
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M62.00012: Kondo resonance assistant thermoelectric transport through strongly correlated quantum dot Yongxi Cheng, jianhua wei, Hong-Gang Luo, Hai-Qing Lin We theoretically study the thermoelectric transport properties of a strongly correlated quantum dot system in the presence of Kondo effect, on the basis of accurate numerical evaluations. The thermocurrent versus gate voltage shows a distinct sawtooth line-shape at high temperature. In particular, the sign of current changes from positive (hole charge) to negative (particle charge) in the electron number N = 1 region due to Coulomb blockade effect. However, at low temperature, where Kondo effect takes place, the thermocurrent charge polarity reverses, together with also a significantly enhanced magnitude. As anticipated, the current sign can be analyzed by the occupation difference between particle and hole. Moreover, one could further define the characteristic turnover temperature, at which the influences of Coulomb blockade and Kondo resonance are in effective balance. When magnetic field is applied, a spin-polarized thermocurrent could be obtained, which could be tested in future experiments. |
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M62.00013: Ballistic p–n junctions in three-dimensional Dirac semimetal Cd3As2 nanowires Minkyung Jung, Janice Bayogan, Sung Jin An, Jungpil Seo We demonstrate a ballistic p−n junction in a three-dimensional Dirac semimetal (DSM) Cd3As2 nanowire with two recessed bottom gates. The device exhibits four different conductance regimes with gate voltages, confirming that device forms p−n junction. The conductance in the p−n junction regime decreases drastically when a magnetic field is applied perpendicular to the nanowire, which is due to the suppression of Klein tunneling. In this regime, the device shows quantum dot behavior. On the other hand, clear conductance plateaus are observed in the n−n regime likely owing to 1-D subbands of carriers at high magnetic fields. In other devices, we also observe Fabry-Perot interference in the p−n junctions, indicating that our devices are in the ballistic regime. Our experiment shows that the ambipolar tunability of DSM nanowires can enable the realization of quantum devices based on electron optics. |
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