Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P62: Electron-Phonon Coupling and Transport in NanostructuresFocus
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Sponsoring Units: DMP Chair: Shixiong Zhang, Indiana Univ - Bloomington Room: Mile High Ballroom 4C |
Wednesday, March 4, 2020 2:30PM - 3:06PM |
P62.00001: A Quantum Dot Heat Engine Invited Speaker: Heiner Linke It has been known for some time that a perfect (delta-function) energy filter allows, in principle, thermal-to-electric energy conversion near ideal (Carnot) efficiency. [1,2] I will introduce this concept and report on a recent experiment where we realized a near-ideal quantum-dot heat engine in devices based on single nanowires, realizing power production at maximum power with Curzon-Ahlborn efficiency, and reaching more than 70% of Carnot efficiency at maximum efficiency settings [3]. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P62.00002: Cooling and self-oscillation in a nanotube electromechanical resonator Carlos Urgell, Wei Yang, Sergio De Bonis, Chandan Samanta, Maria José Esplandiu, Quan Dong, Yong Jin, Adrian Bachtold Nanomechanical resonators are used with great success to couple mechanical motion to other degrees of freedom, such as photons, spins and electrons [1,2]. The motion of a mechanical eigenmode can be efficiently cooled into the quantum regime using photons [2,3,4], but not other degrees of freedom. Here, we demonstrate a simple yet powerful method for cooling, amplification and self-oscillation using electrons. This is achieved by applying a constant (d.c.) current of electrons through a suspended nanotube in a dilution refrigerator. We demonstrate cooling to 4.6±2 quanta of vibrations. We also observe self-oscillation, which can lead to prominent instabilities in the electron transport through the nanotube. We attribute the origin of the observed cooling and self-oscillation to an electrothermal effect. This work shows that electrons may become a useful resource for cooling the mechanical vibrations of nanoscale systems into the quantum regime. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P62.00003: Theory of hot-carrier generation and relaxation in plasmonic nanoparticles Yu Zhang Hot-carrier generation from surface plasmon decay has attracted much recent attention due to its promising applications in physical, chemical, materials and energy science. However, the detailed mechanisms of plasmonic hot-carrier generation and relaxation are less studied or treated by the semiclassical model. In this work, we develop and apply a quantum-mechanical model and coupled master equation method to study the generation, relaxation, and extraction of hot-carriers. And the connection with the semiclassical model is discussed. The initial distribution of hot-carriers and lifetimes of hot-carriers induced by different excitation are investigated. The relaxation due to electron-electron and electron-phonon scatterings are treated on the equal footing. Heat generation from hot-carriers decay is also described. We also generalize the model to study the extraction of hot-carriers to attached molecules or semiconductors. The quantum yield of extracting hot-carriers from the plasmonic nanoparticles is found to be size-dependent. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P62.00004: Nanoimaging of surface waves in 2D materials Dmitri Voronine Propagating surface waves such as surface-plasmon polaritons and exciton-polaritons have recently been of interest in a variety of optical, electronic and quantum communication applications. Nano-optical imaging of surface waves in two-dimensional (2D) transition-metal dichalcogenide (TMD) materials has been realized in several cavity-coupled systems. In this work, new nanoimaging schemes based on tip-enhanced photoluminescence (TEPL) and Kelvin-probe force microscopy (KPFM) are presented, revealing the optical and electric components of surface waves in 2D TMD heterostructures, respectively. These results could be used in novel nanophotonic coupling schemes for quantum emitters in 2D materials. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P62.00005: Coupled electron-phonon thermal transport across metal-nonmetal interfaces and superlattices Cheng Shao, Junichiro Shiomi Understanding the thermal transport across metal/nonmetal interface is of great importance for applications like electronic and thermoelectric devices. In nonmetal phonons are the dominant heat carriers; while in metal both electrons and phonons conduct heat. The nonequilibrium carrier populations and the complicated coupling channels at the interfaces make our current understanding yet to be completed. In this work, we utilize the fully coupled Monte Carlo simulations to study thermal transport across the metal-nonmetal interfaces and superlattice. The mode-wise electron and phonon relaxation times and their coupling strengths are obtained from first-principles calculations, while the phonon transmissions at interfaces are obtained from the Green’s function methods. The simulation results show that the thermal transport at metal/nonmetal interface can be enhanced by inserting an intermediate metal layer with high electron-phonon coupling strength. For metal-nonmetal superlattice structure, thin metal layers with weak electron-phonon coupling can largely impede the thermal transport. The simulation results reveal the importance of mode-wise scattering channel and the nonequilibrium between electron, acoustic phonon, and optical phonon at the interface to thermal transport. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P62.00006: Modification of Electron-Phonon Coupling by Micromachining and Suspension Olli Saira, Matthew Matheny, Libin Wang, Jukka P Pekola, Michael Roukes Weak electron-phonon interaction in metals at low temperatures forms the basis of operation for cryogenic hot-electron detectors. Standard power laws, describing the heat flow in the majority of experiments, have been identified and derived theoretically. However, a full picture encompassing experimentally relevant effects such as reduced dimensionality, material interfaces, and disorder is in its infancy, and has not been tested extensively. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P62.00007: Influence of Highly Non-Equilibrium Electron-Phonon Transport on Heat Conduction across Metal-Insulator Superlattice KYOUNGJUNG KIM, Yosuke Kurosaki, Naoto Fukatani, Shin Yabuuchi, Yusuke Ira, Cheng Shao, Jun Hayakawa, Junichiro Shiomi Nanostructuring is often utilized to improve figure-of-merit of thermoelectric materials by reducing thermal conductivity (TC). There, thermal boundary conductance at nanostructure interfaces is important, and population of heat carriers can be highly non-equilibrium. One strategy to further reduce TC is to utilize metal–semiconductor interfaces, such as in metal-semiconductor superlattice with the electron-phonon scattering mean free path being comparable or longer than the nanostructure length-scale. There, the nonequilibrium interfacial regions are expected to make phonons the dominant heat carrier even in the metal part, which should contribute to the reduction of TC. In this study, we take metal-insulator(MgO) superlattice as a model case and measure the TC by the time-domain thermoreflectance method. We prepare two kinds of samples with different metal layers (AuSi or Ta) with relative difference in the electron-phonon coupling strength. As a result, for both kinds of samples, TC of superlattice was reduced as the unit-layer of the superlattice was made thinner. While the reduction of TC is expected due to the increase in the number of interfaces, the different trends of reduction between AuSi and Ta samples suggest roles of non-equilibrium phonon-electron transport. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P62.00008: Ultrafast investigation of electronic and vibrational dynamics via pump-degenerate four-wave mixing Joseph Avenoso, Daniela Zahn, Ralph Ernstorfer, Lars Gundlach Phonon dynamics and their coupling to electronic excitations in bulk tungsten disulfide is investigated. Pump-degenerate four-wave mixing is used to measure the femtosecond dynamics of the phonons, which when combined with transient absorption spectroscopy, provides an energy-resolved picture of phonon dynamics and their lifetimes. Measurements suggest the LA(M) phonon mitigates electron scattering from the K point to the Σ valley in under 100 fs. Pump-degenerate four-wave mixing is hereby shown to be an effective tool to compliment momentum-resolved methods for studying coupling in tungsten disulfide and other transition metal dichalcogenides. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P62.00009: Acoustoelectric charge transport at the LaAlO3/SrTiO3 interface by surface acoustic waves Yigitcan Uzun, Sander Smink, M. P. de Jong, Hans Hilgenkamp, Wilfred G. van der Wiel Surface acoustic waves (SAWs) are capable of transporting free charge carriers along their propagation path, resulting in an acoustoelectric current or voltage. This has been explored intensively in AlGaAs/GaAs heterostructures. Here, we integrate SAWs with the LaAlO3/SrTiO3 2-dimensional electron system, which is known to exhibit high mobility at low temperature, magnetism and superconductivity under the appropriate conditions. Despite the non-piezoelectric nature of SrTiO3 (and LAO) we can make use electrostriction for SAW generation. We measure the acoustoelectric effect both at room temperature and at 150 K, and observe a considerable enhancement at lower temperatures. Our results suggest robust coupling between the SAWs and the interfacial free electrons, which opens the way for applying the same approach in other non-piezoelectric (complex-oxide) systems. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P62.00010: Hot-carrier induced above-threshold light emission in plasmonic tunnel junctions Longji Cui, Yunxuan Zhu, Mahdiyeh Abbasi, Arash Ahmadivand, Burak Gerislioglu, Peter Jan Arne Nordlander, Douglas Natelson Light emission from electrically driven tunnel junctions, mediated by localized surface plasmons, have attracted much recent interests, showing that the emitted photon energies are limited by the applied voltage bias. Recent works have reported the above-threshold light emission in which the emitted photons have energies significantly above the applied voltage. However, the physical mechanism underlying this phenomenon, is elusive. Here we report systematic measurements of light emission from tunneling junctions made of different plasmonic materials and proposed a hot-carrier induced light emission mechanism. The characteristics and dynamics of the hot carriers is found to be set by the non-radiative plasmonic process. The reported light emission and electrically driven hot carrier generation opens new possibility in plasmonic chemistry and optoelectronic energy conversion applications. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P62.00011: Ultrafast hot carrier injection in Au/GaN: the role of band bending and the interface band structure Fan Zheng, Lin-Wang Wang Plasmon photochemistry can potentially play a significant role in photocatalysis. To realize this potential, it is critical to enhance the plasmon excited hot carrier transfer and collection. However, the lack of atomistic understanding of the carrier transfer across the interface, makes it challenging to design more efficient system. In this work, we apply the non-adiabatic molecular dynamics simulation to study hot carrier dynamics in the system of Au nanocluster on top of GaN surface. By setting up the initial excited hole in Au, the carrier transfer from Au to GaN is found to be on a sub-pico second time scale. After the hole has cooled down to the band edge of GaN, we find some of the charges can return back to Au. By applying different external potentials to mimic the Schottky-barrier band bending, the returning charge can be reduced effectively. Finally, with the understanding of the carrier transfer's pathway, we suggest that a ZnO layer between GaN and Au can effectively block the "cold" carrier from returning back to Au but still allow the hot carrier to transfer. |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P62.00012: Tunable plasmonic hot carrier dynamics in noble metal alloys Adela Habib, Ravishankar Sundararaman Noble metal alloys exhibit promise as a tunable plasmonic material with an 'on-demand optical response' [1]. However, the performance of these metal alloys for plasmonic hot carrier harvesting remains unknown. In particular, disorder in the alloys is expected to lead to increased scattering and inhibit transport of low energy carriers in metal alloys, but the corresponding situation for hot carriers is not yet known. Moreover, hot carrier generation and injection across a metal-semiconductor interface depend sensitively on the band structure [2], and alloys may provide an opportunity to tune the band structure for increasing injection. This talk will present first-principles predictions of hot carrier generation and transport properties of ordered and random structures of gold-silver alloys. The density of states and phase space for both optical excitation and hot carrier scattering depend critically on composition and disorder, providing an additional knob for generating and harvesting hot carriers with desired energy distributions. |
Wednesday, March 4, 2020 5:18PM - 5:30PM |
P62.00013: Non-adiabatic electron pumping driven by continuous bias voltage modulation Kazunari Hashimoto, Chikako Uchiyama Recent developments in nanotechnology enable us to control and observe electron transfer with high accuracy fulfilling needs for quantum metrology. One of its important instances is an electron pump driven by a time periodic bias voltage between source and drain electrodes attached to a microscopic system such as a quantum dot (J. P. Pekola et al., Rev. Mod. Phys. 85, 1421 (2013)). In conventional studies, the electron pump has been mostly formulated in an adiabatic regime, where the time-dependent bias is described by an infinitely slow modulation of electrochemical potentials of electrodes (T. Yuge et al., Phys. Rev. B 86, 235308 (2012)). This formalism is, however, practically useless because the pumped current generated by the infinitely slow modulation is zero in a strict sense. The purpose of the present study is to provide a more realistic formalism describing the pumping under a finite speed continuous modulation of the bias voltage. To this end, we propose an extended formalism of the pumping based on the full counting statistics with quantum master equation taking into account a temporal shift of single-particle energy of electrons in source and drain induced by the voltage modulation. |
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