Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q68: Thermal and Electrical Transport in NanomaterialsFocus Recordings Available
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Sponsoring Units: DMP Chair: Andrea Pickel, University of Rochester Room: Hyatt Regency Hotel -Hyde Park B |
Wednesday, March 16, 2022 3:00PM - 3:36PM |
Q68.00001: Thermal transport in topological electronic and phononic materials Invited Speaker: Bolin Liao Topological materials hold great promise for applications in microelectronics, photonics, and energy harvesting due to ultrahigh mobility, low dissipation, and topologically protected surface states. While their electronic and optical properties have been intensely studied in the past decade, their phononic and thermal transport properties remain less explored. In this talk, I will discuss our recent effort to understand phonon transport and electron-phonon interaction in topological electronic and phononic materials. The examples I will discuss include strong Kohn anomaly in topological Dirac semimetals, phonon softening near topological phase transitions, and novel transport and scattering properties of topological phonons. I will provide some perspectives on the connections among chemical bonds, electronic band topology, and lattice properties. I will also discuss the prospects of utilizing topological materials for thermal management and manipulation and energy harvesting applications. |
Wednesday, March 16, 2022 3:36PM - 4:12PM |
Q68.00002: Dimensionality transition and divergent thermal conductivity observed in thin NbSe3 nanowires Invited Speaker: Deyu Li Fundamental understanding of thermal transport remains an intriguing research topic and a classical anomaly is the divergent thermal conductivity of one-dimensional (1D) lattices, a direct consequence of the classical Fermi-Pasta-Ulam-Tsingou (FPUT) paradox. Extensive theoretical and numerical studies have been carried out, and results indicate superdiffusive phonon transport with the thermal conductivity increasing with the chain length. However, solid experimental evidence has been scarce because of the challenge of measuring thermal transport through single atomic chains of sufficient length. Quasi-1D van der Waals (vdW) crystals with covalently bonded atomic chains assembled together via weak vdW interactions provide unique opportunities to probe the divergent thermal conductivity of 1D phonons. Here we report on systematic experimental studies of thermal transport through quasi-1D NbSe3 nanowires. Results show distinct signatures of electron-phonon scattering in the lattice thermal conductivity of NbSe3 nanowires as charge density wave phase transition occurs. Interestingly, contrary to the classical size effect, the observed thermal conductivity demonstrates a 25-fold enhancement as the nanowire diameter reduces from 26 to 6.8 nm. Examination of the temperature dependence indicates that 1D phonons dominate the thermal transport at elevated temperatures for thin NbSe3 nanowires. At room temperature, the thermal conductivity displays a length dependence extending over 42.5 µm and follows a 1/3 power law with the wire length, which provides experimental evidence for superdiffusive transport. Atomic force microscopy characterization discloses a drastic elastic stiffening effect with a five-fold enhancement of the Young’s modulus for ultr-thin nanowires, which triggers the transition to 1D phonon transport. |
Wednesday, March 16, 2022 4:12PM - 4:24PM |
Q68.00003: Nonlinear IV curves in twisted bilayer graphene Haidong Tian, Shi Che, Fan Zhang, Marc Bockrath, Chun Ning Lau Owing to the flatness of the reconstructed minibands, kinetic energy in twisted bilayer graphene is quenched. Recently, non-linear current-voltage (I-V) characteristics and sharp peaks in differential resistance are observed in graphene-BN superlattices and twisted bilayer graphene away from magic angle[1] at moderate current density, which arise from the Schwinger pair production mechanism in the presence of reduced Fermi velocity. Here, by tuning twisted bilayer graphene near magic angle, we investigate the possibility of further reducing Fermi velocity and the evolution of nonlinear IV curves with strongly correlated behavior turned on. |
Wednesday, March 16, 2022 4:24PM - 4:36PM |
Q68.00004: Collective behavior of electrons beyond hydrodynamic transport Adbhut Gupta, Jean J Heremans, Gitansh Kataria, Mani Chandra, Saeed Fallahi, Geoff Gardner, Michael J Manfra The collective behavior of electrons in hydrodynamic transport regime has been a topic of growing interest due to experimental observations in ultraclean materials. The fluid-like properties in this regime, such as formation of current vortices are attributed to dominance of electron-electron (e-e) scattering. The detection of negative nonlocal resistance is often regarded as the hallmark signature of hydrodynamic regime. Through nonlocal resistance measurements and high-resolution kinetic simulations performed in large-scale ultraclean (electron mean-free ~ 65 μm at 4.2 K) GaAs/AlGaAs devices, hosting numerous point contacts, we demonstrate that both current vortices and negative nonlocal resistance are not exclusive to hydrodynamic regime. Despite the absence of dominant e-e scattering, current vortices and negative nonlocal resistance can form even in the ballistic transport regime. These striking similarities in ballistic and hydrodynamic regimes stem from total electron system momentum conservation in the bulk in both regimes. The collective effects observed in ballistic regime, which is often understood from a single-particle picture, shed a new light on the dynamics of electrons in mesoscopic transport. |
Wednesday, March 16, 2022 4:36PM - 4:48PM |
Q68.00005: Negative Differential Conductance and Electron Interference Effects in GaN/AlN Resonant Tunneling Diodes with Metallic Collector Jimy Encomendero, Vladimir Protasenko, Debdeep Jena, Grace Xing Resonant tunneling transport in semiconductor heterostructures that exhibit broken inversion symmetry due to spontaneous and piezoelectric polarization fields has been under scrutiny over the last few years [PRX 7, 041017 (2017)]. Engineering this quantum transport regime in polar III-Nitride semiconductors is of high interest for manufacturing ultra-fast electronic oscillators and intersubband lasers. Towards this goal, we have recently elucidated the implications of the broken inversion symmetry on the quantum transport characteristics of GaN/AlN resonant tunneling diodes (RTDs) [PRApplied 11, 034032 (2019)]. This new understanding on broken-symmetry effects has prompted us to study the possibility of recovering symmetric resonant tunneling injection using a metallic collector to screen polarization charges [PRApplied 13, 034048 (2020)]. Here, we report the transport characteristics of such RTD structure in which the n-type GaN collector layer is replaced with the Ti/Au/Ni metallic stack. Thanks to the exponentially enhanced resonant tunneling transmission of carriers, this novel heterostructure design enables the injection of electrons directly from the metallic collector into the wide-bandgap semiconductor. Repeatable room-temperature negative differential conductance is measured in multiple devices, attesting to the high degree of electronic coherence. Temperaturature-dependent resonant tunneling spectroscopy of the polar heterostructure is also reported between 4.2K and 300K. Moreover, the robustness of this quantum interference phenomenon is verified by the generation of self-sustained microwave oscillations with a fundamental frequency of 0.22 GHz. These results raise hopes for the development of fully-epitaxial resonant tunneling structures capable of seamlessly interfacing III-Nitride semiconductor devices with strongly correlated materials, including superconductors and ferromagnets, thereby enhancing Andreev reflection and spin injection, respectively. |
Wednesday, March 16, 2022 4:48PM - 5:00PM |
Q68.00006: Understanding Anisotropy of photoconductance in In4Se3: insights from DFT Duy Le, Xiao C Zeng, Peter A Dowben, Alexey Lipatov, Archit Dhingra, Nataliia Vorobeva, Alexander Sinitskii, Talat S Rahman Although In4Se3 has a layered structure with the ionic character of the interlayer interactions.1 In the crystal structure of In4Se3, [(In3)5+(Se2-)3]- clusters are interconnected along both c and b axes forming a quasi-2D layer intermitted with chains of ionized In+. Cleaving along bc plane results in a surface with 1D chain of Se and In atoms thus the electronic structure and photoconductance of the surface are expected to be anisotropic. Density functional theory calculations for the bc surface of In4Se3 show that the frontier orbitals are dominated by s, pz and py character, not px, suggesting that s to pz transitions are allowed with the light vector potential aligned along the surface normal, s to py transitions are allowed with the light vector potential aligned in-plane but orthogonal to the chains, but there is little opportunity for px to d and s to px transitions. Experimental investigations of the optical photoconductance anisotropy performed on devices based on In4Se3 flakes with signatures of quasi-1D chains confirm the above findings.1 These open new pathways for application of In4Se3 in efficient integration of logic and sensing. |
Wednesday, March 16, 2022 5:00PM - 5:12PM |
Q68.00007: High transparent conductor figure-of-merit in SrVO3 grown by solid-phase epitaxy Samuel D Marks, Lin Lin, Peng Zuo, Patrick J Strohbeen, Ryan Jacobs, Dongxue Du, Jason Waldvogel, Rui Liu, Donald E Savage, Susan E Babcock, Jason Kawasaki, John H Booske, Dane Morgan, Paul G Evans SrVO3 thin films with a high optical transparency and electrical conductivity were formed by crystallizing amorphous layers using solid-phase epitaxy (SPE). Epitaxial complex oxides incorporating transition metal ions can be formed by SPE with thermodynamics and kinetics derived from crystallization processes that are initiated at buried amorphous/crystalline interfaces. Thermodynamic calculations predict the temperature and oxygen partial pressure conditions required to produce the SrVO3 phase and match the experimental conditions. The lattice parameters and mosaic angular width of x-ray reflections from the crystallized films show that the 16 nm layers are coherently strained. The strain resulting from the epitaxial mismatch between SrVO3 and SrTiO3 is relaxed in the 60 nm layer. SrVO3 layers with 16 nm thickness exhibited a room temperature resistivity of 5.2 × 10-5 Ω cm and visible light transmission of 0.89. Increasing the film thickness resulted in lower room temperature resistivity and a significant reduction in optical transparency. Temperature-dependent resistivity measurements between 5 K and 300 K reveal residual resistivity ratios of 2 and 3.8 for 16 and 60 nm SrVO3 layers, respectively. The temperature dependence of the resistivity for SPE-grown SrVO3 will be discussed, including the effect of electron scattering from structural defects at low temperatures. |
Wednesday, March 16, 2022 5:12PM - 5:24PM |
Q68.00008: Aharonov-Bohm effect for the network of critical trajectories near Lifshitz transition leads to precursors of Brown-Zak oscillations. Sergey Slizovskiy, Folkert K De Vries, Petar Tomic, Aitor Garcia-Ruiz, Giulia Zheng, Elias Portoles, Kenji Watanabe, Takashi Taniguchi, Vladimir Fal'ko, Klaus Ensslin, Thomas Ihn, Peter Rickhaus Moiré quasi-crystals open previously inaccessible regimes of Fermi surface (FS) topologies. We consider the magnetotransport in the vicinity of Lifshitz transitions that happen when the size of FS compares to the size of mini-Brillouin zone and the FS touches with its copy in the next unit cell. As a result, FS forms an infinite periodic 2D network. In a perpendicular magnetic field, electrons drift in a fixed direction along the edges while having a choice (determined by the amplitude of magnetic breakdown) where to go at each vertex. |
Wednesday, March 16, 2022 5:24PM - 5:36PM |
Q68.00009: Controlled confinement of electron vacuum states through atomic engineering Rasa Rejali, Laëtitia Farinacci, David Coffey, Jeremie Gobeil, Yaroslav M Blanter, Sander Otte Metal interfaces with a surface-projected band gap can host localized electronic states at the vacuum level: field emission resonances. While these states arise from confinement in the direction perpendicular to the surface, they are typically unconfined in the remaining directions. Here, we use atom manipulation of surface vacancies in a chlorine-terminated Cu(100) surface to engineer lateral confinement: we arrange the vacancies to reveal square patches of the underlying metal surface, creating atomically precise potential wells that host particle-in-a-box modes. The quantum numbers of these states can be tuned by adjusting the shape and size of the confined patches, making them attractive candidates as artificial quantum dots. The added confinement also renders the wavevector, k, a bad quantum number in all directions, thereby creating direct tunnelling paths from the vacuum-localized resonance to the bulk crystal that do not exist otherwise. As such, the resonances become critically dependent on the bulk band structure, resulting in negative differential resistance in the voltage range in which the band edge is upward sloping. Our results provide possible avenues for engineering atomic-scale resonant tunnelling diodes, which exhibit similar current-voltage characteristics. |
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