Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y12: Thermodynamic and Transport PropertiesRecordings Available

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Sponsoring Units: FIAP Chair: Frances Hellman, University of California, Berkeley Room: McCormick Place W181C 
Friday, March 18, 2022 8:00AM  8:12AM 
Y12.00001: Anisotropic Electronic Transport Properties of ReSe_{2} FieldEffect Transistors Brian A Holler

Friday, March 18, 2022 8:12AM  8:24AM 
Y12.00002: The magnetotransport in the quantum wires comprised of vertically stacked quantum dots Manvir S Kushwaha We investigate a periodic system of vertically stacked InAs/GaAs quantum dots (VSQD) subjected to a twodimensional confining harmonic potential and a magnetic field in the symmetric gauge. Given the tiny length scales, adequate lateral confinement, and strong vertical coupling involved in the experiments, the VSQD system has become known for mimicking the standard semiconducting quantum wires. An exact analytical diagnosis of the problem allows us to show the system's direct relevance to the physics of musical sounds, magnetization, magnetotransport, and designing of the optical amplifiers. The results suggest making the most of the system for applications in singleelectron devices and 
Friday, March 18, 2022 8:24AM  8:36AM 
Y12.00003: Probing the Dynamics of Electric DoubleLayer Formation Over Wide Time Scales (10^{9} – 10^{+5} s) in the Ionic Liquid DEMETFSI Shenchu Yin, Jonathan P Bird, keke he, Michael D Randle, Bilal Barut, Ripudaman Dixit, Alexey Lipatov, Alexander Sinitskii Ionic liquids (ILs) have found wide use as the gate dielectric in a variety of novel transistors, allowing large carrier concentrations to be induced. These concentrations arise from the formation of an electric double layer (EDL) at the interface between the liquid and the channel, a process that yields an extremely high effective areal capacitance. ILs have been used to gate a variety of different materials, including polymers, oxides and lowdimensional materials, and have led to the discovery of exciting fundamental phenomena. In this work, we investigate the transient response of DEMETFSI [N, NdiethylN(2methoxyethyl)Nmethylammonium bis(trifluoromethylsulfonyl)imide] based ionicliquid (IL) planar capacitors, studying this response over time scales as short as a few nanoseconds, to as long as several days. Our measurements point to the existence of three distinct mechanisms for charging/discharging of the IL. The fastest of these is associated with the development of a standard polarization charge in the bulk of the liquid dielectric, which dominates at times shorter than ~10^{6} s. The second process is attributed to electric double layer formation, which is initiated after ~10^{6} s but which takes as long as ~10^{2} s to reach completion. Finally, we also identify the presence of a pseudocapacitance that arises from electrochemical reactions; this process is only activated at voltages above ~2.5 V and is relatively slow. Indeed, we find evidence that full discharging of this pseudocapacitance can take as long as 10^{5} s (i.e., days). Overall, our findings provide useful insight into the mechanisms for slow ion dynamics in ILs, and highlight the constraints that these dynamics place on the potential operational speed of ILbased transistors. 
Friday, March 18, 2022 8:36AM  8:48AM 
Y12.00004: Ballistic and diffusive phonon heat transport studied by pulse propagation in one dimension Philip B Allen, Nhat A Nghiem Several kinds of heat pulses are inserted into a onedimensional lattice. Their propagation is studied in classical mechanics, which gives insight into ballistic versus diffusive behavior. The results are modeled using quasiparticle pictures, especially the phonon Boltzmann equation. Ballistic propagation is easily modeled, has interesting dependence on the shape of the initial insertion, and gives insight into new aspects of Boltzmann theories of systems inhomogeneous in space and time. Phonon scattering provides an approach to diffusive propagation. Scattering by impurities with altered mass give new features to the propagating pulse, as does anharmonic phononphonon coupling. The Boltzmannpredicted pulse shapes using relaxationtime approximation show a crossover toward diffusion, but do not agree closely with the simulations. 
Friday, March 18, 2022 8:48AM  9:00AM 
Y12.00005: Electrical transport of graphenecontacted thin layer pentagonal transition metal dichalcogenide (TMDC) Yuxin Zhang 2D materials with puckered pentagonal structures have been predicted to show exotic new properties due to inplane anisotropy. Yet there have been limited experimental transport studies on such materials due to the scarcity of this type of materials and difficulties in achieving ohmic contact, especially for thin layers that have larger band gaps. Most of the current studies focus on Palladium diselenide PdSe2, which is air stable and can be mechanically exfoliated into thin layers. In this work, we use graphene to contact atomically thin PdSe2, which significantly reduces the contact resistance, therefore facilitated magnetotransport studies at low temperatures and enabled observation of new features that have never been discussed in previous studies. 
Friday, March 18, 2022 9:00AM  9:12AM 
Y12.00006: A simple method to calculate specific heat at constant pressure from first principles Christopher M Stanley Calculating specific heat at constant pressure (Cp) entirely from firstprinciples has historically proven difficult, and what few methods which do exist are complex and require significant effort to implement. In this work, we describe a different method for calculating Cp which is entirely based on firstprinciples, density functional theory. It is conceptually simple, computationally efficient and easy to implement because it avoids the need for finite temperature density functional theory. In order to demonstrate the accuracy, precision and validity of our method, we present and discuss data and results for wellstudied, benchmark semiconducting materials Si and Ge, where our results agree well with the prevailing literature. We also go further and calculate Cp for wurtzite GaN, a material for which there is no prevailing consensus. We use our calculated values and a review of the literature to determine a set of recommended values for GaN. 
Friday, March 18, 2022 9:12AM  9:24AM 
Y12.00007: Decoupling between propagating acoustic waves and twolevel systems in hydrogenated amorphous silicon Manel MolinaRuiz, Hilary C Jacks, Daniel R Queen, Thomas H Metcalf, Xiao Liu, Frances Hellman Tunneling twolevel systems are the dominant energy loss mechanisms for amorphous solids at low temperatures. Hydrogenated amorphous silicon is one of the few materials that shows mechanical loss values below the “glassy range,” which indicates a low density of tunneling twolevel systems at low temperature. We have measured the specific heat of hydrogenated amorphous silicon prepared by hotwire chemical vapor deposition, which shows a large density of twolevel systems. Annealing at 200 °C, well below the growth temperature, does not significantly affect the alreadylow mechanical loss, but irreversibly reduces the specific heat by an order of magnitude at 2 K, indicating a large reduction in the density of twolevel systems. We compare the specific heat with the internal friction results, which suggest that the twolevel systems are uncharacteristically decoupled from acoustic waves, both before and after annealing. Our analysis yields an anomalously low value of the coupling constant , which increases upon annealing but remains anomalously low. The results suggest that the coupling constant value is lowered by the presence of hydrogen. 
Friday, March 18, 2022 9:24AM  9:36AM 
Y12.00008: Refinement of the TwoBand Model Using Nonsaturating Magnetothermoelectric Coefficients in the Highly Compensated Semimetal NbSb_{2} Ian Leahy, Peter Siegfried, Andrew Treglia, Minhyea Lee With growing interest in the magnetothermoelectric properties of semimetals, it becomes pertinent to develop and analyze methods for classifying and modeling their thermoelectric responses. We study the temperature and magnetic field dependence of the Seebeck and Nernst coefficients in the compensated semimetal NbSb_{2}. At low temperatures and high fields, we find that the Seebeck coefficient increases quadratically and the Nernst coefficient increases linearly as a function of field without signs of saturation up to 14T. We present a new analysis of magnetothermoelectricity in highly compensated semimetals, where the linear and quadratic field dependences of the Seebeck and Nernst signals impose stringent limitations on 2 band model fitting of the electrical conductivity, tightly constraining the carrier densities and mobilities [1,2]. We will discuss the implication of our results on the nonsaturating nature of the magnetoresistance and magnetothermoelectric effects. 
Friday, March 18, 2022 9:36AM  9:48AM 
Y12.00009: 1D Coulomb drag in the ultralow temperature limit Harith Kassar, Rebika Makaju, Sadhvikas Addamane, Dominique Laroche We report temperature dependence measurements of 1D Coulomb drag in GaAs/AlGaAs quantum wires. Utilizing enhanced filtering and a nuclear magnetization stage, 1D electron temperatures below 10 mK have been achieved. The drag resistance R_{D} exhibits the standard modulation as the wires’ subband occupancy is varied. The temperature dependence of R_{D} as a function of both subband occupancy and interwire separation has been studied. The qualitative and quantitative functional shape of this dependence is utilized to determine the parametric evolution of the dominant drag inducing scattering mechanisms in the ultralow temperature limit. 
Friday, March 18, 2022 9:48AM  10:00AM 
Y12.00010: Competing drag inducing mechanism in quasi1D quantum wires Rebika Makaju, Harith Kassar, Sadhvikas Addamane, Dominique Laroche We report 1D Coulomb drag measurements in laterallycoupled single layer GaAs/AlGaAs quantum wires. The drag resistance RD exhibits the standard modulation as the wires’ subband occupancy is varied. In contrast to previous Coulomb drag studies in onedimensional GaAs systems, both symmetric and antisymmetric components to the drag signals are observed upon current reversal, highlighting the presence of competing draginducing mechanisms. The dependence of each contribution is studied as a function of both current amplitude and temperature. The antisymmetric results are compared with theories for momentum transferinduced drag while the symmetric contribution is interpreted in terms of a rectification of charge fluctuations. 
Friday, March 18, 2022 10:00AM  10:12AM 
Y12.00011: Thermal runaway of Sibased metasurfaces under highpower illumination Gabriel R Jaffe, Gregory R Holdman, Min Seok Jang, Demeng Feng, Mikhail A Kats, Victor W Brar Sibased dielectric metasurfaces can be used to make compact optical components such as lenses, polarizers, gratings, and highly reflective surfaces. Si is a particularly attractive material for use in highpowerdensity applications such as nonlinear microscopy, telecommunications, and laserpropelled light sails because of its low absorptive loss at infrared frequencies. In this work, we assessed the thermal stability of radiatively cooled Si/SiO_{2} metasurfaces subjected to high optical fluxes (>1 GW m^{2}) of 1550 nm light using a broadspectrum and temperaturedependent absorption model for Si that we assembled from multiple literature sources. We found that nonlinear absorption effects at low temperatures in conjunction with a shrinking bandgap and rising freecarrier absorption at high temperatures can result in a thermal runaway effect that ultimately destroys the metasurface. Furthermore, we find that small hotspots caused by defects or dust can push an otherwise thermally stable metasurface into thermal runaway. We will discuss in detail the physical phenomena driving this thermal runaway in Si, evaluate the absorption and emission contributions of the SiO_{2} layer, and set limits on the maximum optical intensity a Sibased metasurface can survive. 
Friday, March 18, 2022 10:12AM  10:24AM 
Y12.00012: Universal features of dynamics of localized electronic states Anatoly Obzhirov, Eric J Heller In a number of systems, electronic transport can be viewed as dynamics of localized electronic states. However, there is no universal theory that describes time evolution of localized states. In this work, we present universal features of such motion. They originate from the concept of adiabatic change of character near an avoided crossing. It is shown that localized electronic states move by interchanging positions with adjacent localized states that form an avoided crossing. Avoided crossings formed by two adjacent electronic states would be adiabatic, whereas avoided crossing formed by two distant electronic states would be diabatic. To illustrate this idea, we develop a numerical model based on Anderson localized states. Based on our observations, we discuss universal features of relaxation time. The presented perspective could give new insights on MetalInsulator transitions and electron transport in nanostructures, superlattices, and disordered semiconductors. 
Friday, March 18, 2022 10:24AM  10:36AM 
Y12.00013: Wannier interpolation of electronphonon coupling in doped semiconductors Francesco Macheda, Paolo Barone, Francesco Mauri The accurate theoretical calculation of the electronphonon coupling interaction (EPCI) on very fine reciprocal space grids is of crucial importance in order to predict and interpret transport experiments. Such demanding evaluation of the EPCI has become possible for undoped semiconductors with the use of the Wannier interpolation technique, in conjunction with the development of fast and highly scalable abinitio computational infrastructures. On the contrary, despite the plethora of recent advances, the realistic description of the EPCI for doped 3d and 2d semiconductors on fine reciprocal space grids has been hindered by the lack of a welldefined and fast method to interpolate the interaction. In this talk we overcome this limitation and propose a precise, stable and fast technique based on firstprinciples calculations and Wannier interpolation to obtain the correct EPCI for the case of doped 3d and 2d semiconductors. For polar materials, this is of particular importance since stateoftheart transport calculations incorrectly employ the EPCI evaluated in the undoped setup, leading to a large underestimation of the dielectric screening and a proportional overestimation of the interaction, and thus to an incorrect evaluation of the transport coefficients. 
Friday, March 18, 2022 10:36AM  10:48AM 
Y12.00014: A comparative study of phonon anharmonicity and lattice thermal transport with perturbation theory and molecular dynamics Zezhu Zeng, Yue Chen Phonon properties are crucial to determine the intrinsic lattice thermal transport of strongly anharmonic materials. Using the stateoftheart perturbation theory (PT) including up to the fourthorder anharmonicity and molecular dynamics (MD) with accurate firstprinciplesbased machine learning potential, we calculated the phonon lifetimes and lattice thermal conductivities of strongly anharmonic materials Tl_{3}VSe_{4} and BaAg_{2}Te_{2}. We find that PT underestimates the phonon scatterings in the entire Brillouin zone for Tl_{3}VSe_{4} and BaAg_{2}Te_{2} at room temperature, and the calculated phonon lifetimes based on MD simulations show a better agreement with experimental results. Using unified theory on top of accurate phonon properties, we reveal a significant twochannel lattice thermal transport in these strongly anharmonic materials at high temperatures. Our results pave the avenue for future studies of phonon properties and ultralow lattice thermal conductivities of strongly anharmonic crystals beyond the conventional PT realm. 
Friday, March 18, 2022 10:48AM  11:00AM 
Y12.00015: Thermoelectric transport through a quantum dot embedded between Majorana bound states Juan P Ramos Andrade We study a system composed of leads connected to a quantum dot (QD) embedded between two 1D topological superconductors hosting Majorana bound states (MBSs) at their ends. These topological nanowires are treated by means of the Kitaev effective model, which physical realizations have been achieved using hybrid structures semiconductors/superconductors (such as InAsAl), in presence of the magnetic field. The MBSs in such structures interact between them through a coupling that exponentially decays with the wire length. The interplay between discrete energy levels and continuum energy produces interference phenomena, such as the Fano effect. This leads to a violation of the WiedemannFranz law and to an increment in the thermoelectric quantities of the system consequently. Working components mentioned above are present in our system, thus our goal is to provide thermoelectric features of the QD influenced by the connection of MBSs belonging to both topological wires. Our results are obtained in the linear response regime using a temperature difference $\Delta T$. Our findings show that the thermoelectric quantities can be tuned by controlling the tunneling couplings in the system, as well as the phase difference between topological superconductors, leading to its suppression. 
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