Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R27: Thermal and Ballistic Transport in Semiconductors 
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Sponsoring Units: FIAP Chair: Benjamin Fregoso, Kent State Univ  Kent Room: 404 
Thursday, March 5, 2020 8:00AM  8:12AM 
R27.00001: Nondegenerate heavy electrons and Planckian limit to scattering in doped strontium titanate Clement Collignon, Benoit Fauque, Kamran Behnia The metallicity of lightly doped SrTiO_{3} is strange. The combination of the effective mass extracted from quantum oscillations and the amplitude of roomtemperature mobility implies a meanfreepath (mfp) below the Mott Ioffe Regel (MIR) limit and a scattering time shorter than the Planckian time (τ_{P}=h/2πk_{B}T). Here, we present a study of electric resistivity and thermoelectric power above room temperature pointing to a possible exit out of this maze. According to our data, resistivity is metallic and does not saturate up to 900 K. In the nondegenerate regime, the Seebeck coefficient is set by the ratio of the de Broglie wavelength, λ_{dB}, to the interelectron distance, n^{1/3}. We demonstrate that the temperature dependence of the shrinking λ_{dB} (before its saturation to a length twice the lattice parameter) points to a continuous change in the effective mass of charge carriers. Combining the latter with mobility keeps the mfp above the MIR limit and the scattering time longer than τ_{P}. Our results imply the existence of a hitherto unknown case of nondegenerate metallicity driven by temperatureinduced mass amplification. 
Thursday, March 5, 2020 8:12AM  8:24AM 
R27.00002: Energetics of solidstate metathesis reactions in nanostructured thermoelectric systems Xia Hua, Jeff W Doak, Christopher Mark Wolverton Thermoelectric systems with large compositions of AB (e.g. SnTe) and much smaller compositions of A’B’ (e.g. CdS, ZnS) are promising candidates since the secondphase nanostructures scatter phonons, reducing lattice thermal conductivity and increasing ZT. In this work, we use highthroughput density functional theory (DFT) calculations to evaluate the metathesis reactions (AB+A'B'↔A'B+AB') of 1638 quaternary phase systems (A,A’)(B,B’) in order to understand the behaviors and predict potential nanostructured thermoelectrics. We include systems most relevant for rocksaltbased thermoelectrics: group II, IIb, and IV cations, and group VI anions. In addition, we include group III cations and group V anions as possible secondary phases. We find that the metathesis reactions exhibit welldefined trends, which can be explained within the context of hardsoft acidbase theory (HSAB). Deviations from these trends are examined in more detail and finite temperature effects are investigated for select systems. 
Thursday, March 5, 2020 8:24AM  8:36AM 
R27.00003: The thermoshape voltage induced by quantum shape effects Altug Sisman, Alhun Aydin, Jonas Fransson We propose here a new effect for the conversion of heat energy into electricity with nanostructures. We recently used sizeinvariant shape transformation to completely separate quantum size and shape effects from each other, which allows one to focus on purely quantum shape effects. In this work, we first present the existence of the quantum shape effects on thermoelectric transport properties of GaAs nanostructures at ballistic regime. Then we consider a junction composed of the same material having exactly the same geometric sizes, but distinct shapes. We show that an electric voltage is induced under a temperature gradient in such a junction because of the quantum shape effects on Seebeck coefficients. This cross effect is called the thermoshape effect. Our calculations based on Landauer formalism predict that the thermoshape voltage is persistent and in the order of mV/K for nondegenerate GaAs semiconductors. Our study explicitly suggests how important the effect of overall geometry is in nanoscale thermoelectric materials, and can be utilized even if all sizes are the same. A thermoshape junction not only represents a viable setup for the macroscopic manifestation of quantum shape effects, but also constitutes their first possible device application. 
Thursday, March 5, 2020 8:36AM  8:48AM 
R27.00004: Observation of anomalous Shapiro steps in ballistic Josephson junctions of InAs nanowires Kento Ueda, Sadashige Matsuo, Hiroshi Kamata, Yuusuke Takeshige, Yosuke Sato, Shoji Baba, Lars Samuelson, Kan Li, Soren Jeppesen, Hongqi Xu, Seigo Tarucha Advances in semiconductor technology provide the high electric controllability and long mean free path in various kinds of nanostructure. Especially proximityinduced superconductivity in semiconductor nanowire (NW)superconductor junctions provides intriguing platforms to study exotic superconducting phenomena occurring in the ballistic transport regime. 
Thursday, March 5, 2020 8:48AM  9:00AM 
R27.00005: Ballistic transport in black phosphorus transistors Xuefei Li As a strong candidate for future electronics, atomically thin black phosphorus (BP) has attracted great attention in recent years due to its tunable bandgap and high mobility. Here we show that the transport properties of BP device under high electric field can be improved greatly by the interface engineering of highquality HfLaO dielectrics and transport orientation. By designing the device channels along the lower effective mass armchair direction, a record high drive current up to 1.2 mA/μm at 300 K and 1.6 mA/μm at 20 K can be achieved in a 100 nm backgated BP transistor, surpassing any twodimensional semiconductor transistors reported to date. The highest hole saturation velocity of 1.5×10^{7} cm/s is also achieved at room temperature. Ballistic transport shows a record high 36% and 79% ballistic efficiency at room temperature and 20 K, respectively, which are also further verified by theoretical simulations. 
Thursday, March 5, 2020 9:00AM  9:12AM 
R27.00006: Quantum Technologies using Ge and GeSn on Si. Yilmaz Gul, Stuart Nicholas Holmes, maksym myronov, Michael Pepper

Thursday, March 5, 2020 9:12AM  9:24AM 
R27.00007: Thermal transistor and thermometer based on coupled quantum dot and point contact Jing Yang, Cyril Elouard, Janine Splettstoesser, Björn Sothmann, Rafael Sánchez, Andrew N Jordan We propose a threeterminal setup consisting of a Coulomb coupled quantum dot quantum point contact. The source and drain reservoirs are connected to the QPC while the base reservoir is tunnel coupled to the Coulomb blockade quantum dot, which can contain at most one electron. We show that the setup can work as a nanoscale thermal transistor to control the electric or heat current flow in the quantum point contact. Alternatively, by detecting the electric current in the quantum point contact, the setup can also act as the nanoscale thermometer. We calculate the sensitivity and power gain for the transistor and the sensitivity for the thermometer respectively. We derive the operating condition maximizing their respective sensitivities. We show that the resolution in previous experiments on temperature sensing can be further improved if it is tuned to the optimal regime we derived here. 
Thursday, March 5, 2020 9:24AM  9:36AM 
R27.00008: Hopping conduction characterization in amorphous semiconductors and crosslinked metal nanoparticles Brianna Western, Michael Harcrow, Athanasios J Syllaios, Vincent Lopes, Christopher Littler, ZhiGang Yu, Ray Gunawidjaja In amorphous semiconductors, e.g. aSi, conduction occurs via charge carrier hopping between localized states. The key figures of merit in characterization, particularly in microbolometer applications, include the temperature dependence of conductivity, summarized by the temperature coefficient of resistance (TCR), and electrical noise, which are controlled in the hopping regime by the hopping conduction parameters. For nextgeneration bolometer material, crosslinked metal nanoparticles (CLMPs) conduction occurs via electron hopping between adjacent nanoparticles, and the conductivity exhibits Arrhenius temperaturedependent behavior. In these systems, TCR and noise are theorized to be controlled by nanoparticle diameter and separation distance between adjacent nanoparticles, respectively. Diameter and separation distance in CLMPs are independent of each other, with the separation distance being controlled by organic ligands bonded to the nanoparticle surface. This work examines the effect of different organic ligands on electrical conductivity and TCR in CLMPs. 
Thursday, March 5, 2020 9:36AM  9:48AM 
R27.00009: Nonequilibrium nature of nonlinear optical response: Application to the bulk photo voltaic effect Tamoghna Barik, Jay Sau The bulk photovoltaic effect (BPVE) is an example of nonlinear optical response that leads to a DC current in noncentrosymmetric materials which is relevant to photovoltaic applications. We theoretically study this effect in the presence of electronphonon interactions. Using the response function formalism, we show that the nonlinear optical response, in general, contains correlator of three operators which are not ordered in time. This out of timeordered correlator (OTOC) for an interacting system cannot be calculated using equilibrium field theory. Using a semiclassical approach instead, we show that BPVE can be attributed to the dipole moment of generated electron hole pairs. We confirm the validity of semiclassical result for the nonlinear DC response from a quantum master equation approach. From this formalism we also find that the electronphonon coupling strength has a strong implicit effect on the scaling dependence of the nonlinear DC response on the optical field. Most interestingly, the semiclassical treatment shows that the nonlinear DC response for spatially inhomogeneous excitation profiles is strongly nonlocal and must involve the aforementioned OTOC that cannot be computed by equilibrium field theory. 
Thursday, March 5, 2020 9:48AM  10:00AM 
R27.00010: Measurement of Hall conductivity near the metal insulator transition by torque magnetometry Samuel Mumford, Tiffany Paul, Seung Hwan Lee, Amir Yacoby, Aharon Kapitulnik We study Hall conductivity near the disorderinduced metalinsulator transition and present the first measurements of Hall conductivity utilizing a torque magnetometry method. A Corbino disk exhibits a magnetic dipole moment proportional to Hall conductivity when voltage is applied across a test material. This magnetic dipole moment can be measured through torque magnetometry. The symmetry of this contactless technique allows us to measure the Hall conductivity of insulating materials and materials near the metalinsulator transition such as sputtered indium tin oxide. We have measured the Hall conductivity of indium tin oxide with a ratio of transverse to longitudinal resistivity of 1E4 and can now measure Hall conductivity independently of longitudinal resistance. 
Thursday, March 5, 2020 10:00AM  10:12AM 
R27.00011: Kinetic Inductance in Ballistic Transport
Jashan Singhal^{1} and Debdeep Jena^{1,2,3}
1 School of Electrical and Computer Engineering, Cornell University
2 Department of Materials Science and Engineering, Cornell University
3 Kavli Institute at Cornell for Nanoscale Science, Cornell Jashan Singhal, Debdeep Jena Electron transport in nanoscale semiconductors approaches the ballistic limit. Without scattering, the kinetic inductance (KI) of carriers becomes considerably large [1,2]. What are the consequences in devices and circuits? We investigate the generalized kinetic inductance in a ddimensional conductor with various bandstructures (e.g. parabolic and conical) in the ballistic limit. The KI per unit length is evaluated as a function of carrier density and temperature at low bias voltages. The KI is found to very weakly depend on V, and strongly on the electron density. An increase in KI at low density is expected because more velocity is needed to maintain the same current. The ballistic model predicts that even without considering phonon scattering, the KI decreases at high temperature. Because of the Fermionic nature of electrons, their collective excitation exhibits a Newtonian inertia, which decreases with an increase in temperature. The quantum mechanical ballistic KI is compared to the standard ‘classical’ inductance, and its importance is classified for various carrier densities, and dimensions. 
Thursday, March 5, 2020 10:12AM  10:24AM 
R27.00012: Novel computational approach for electrontransport from firstprinciples Alex Ganose, Junsoo Park, Anubhav Jain Accurate calculation of transport properties has so far proved challenging due to the difficulty of computing carrier relaxation times. Methods which explicitly include electronphonon interactions, such as ElectronPhonon Wannier (EPW), yield highquality predictions but are incredibly computationally expensive and therefore limited to systems with few electrons. Conversely, using the constant relaxation time approximation (CRTA), predictions are obtained quickly but can be unreliable. 
Thursday, March 5, 2020 10:24AM  10:36AM 
R27.00013: A model of dephasing in shift current processes Benjamin Fregoso The shift current is a second order nonlinear effect in the optical field thought to be the dominant transport mechanism in many ferroelectric materials and to carry information about the topology of the Bloch wave functions. The shift current requires quantum coherence in the solid. We construct a simple model of electrons coupled to a chain of onedimensional ions lacking inversion symmetry. We analyze the thermalization of electrons within the model at high and low excitations frequencies (close to the band edge). The model allows the study of decoherence in shift current process beyond the classical transport regime. 
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