Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F12: Electronic Structure: Thermodynamic and Optical PropertiesRecordings Available
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Chair: Lei Kerr, FIAP Room: McCormick Place W-181C |
Tuesday, March 15, 2022 8:00AM - 8:12AM |
F12.00001: Strain Effects on the Electronic States, Phonon Modes, and Electron-Phonon Coupling in Cubic Spinel ZnGa2O4 Marco D Santia, Lei Kerr, Stefan C Badescu, Kevin Leedy, Trevor Karnehm In recent years, ultra-wide bandgap ZnGa2O4 (ZGO) has become of great interest as a potential candidate in high power semiconductor device applications. The material possesses highly desirable electrical characteristics and has been synthesized as thin-films using PLD and MOCVD techniques on a number of substrate materials. To better characterize the properties of these PLD grown materials, we utilize first-principles calculations to determine the role of strain on the band structure, lattice configuration, phonon properties and electron-phonon coupling. By adopting hybrid functionals in a density functional theory framework, we observe the strain-dependence on the indirect bandgap of ZGO and construct the numerical deformational potential coefficients. Similarly, we present the dependence of raman-active phonon modes on uniaxial and hydrostatic strain and give raman coefficients of the ideal material. The results presented here will facilitate rapid and non-destructive strain characterization of PLD grown ZGO films as well as strain-engineering electrical properties such as mobility. We combine these with the effect of strain on electron-phonon scattering rates to gain an insight into key factors affecting the carrier mobility |
Tuesday, March 15, 2022 8:12AM - 8:24AM |
F12.00002: Magneto- and thermal-transport properties of Ge2Sb2Te5 Ming Yin, Rongying Jin, Lei Wang, Timir Datta The chalcogenide Ge2Sb2Te5 (GST225) and related ternary systems are exemplars of the sensitive interplay of structure, chemical composition, electronic and thermal properties. Here experimental details and numerical results on properties of bulk poly-crystalline GST225 will be presented. We find that the zero field (B=0) resistivity r(T) decreases with decreasing temperature, which can be quantitatively described by the Block- Gruneisen formula with a Debye temperature (QD) around 120 K. A positive magnetoresistance i.e., increase in resistance with applied B and a modest one order of magnitude raise between 0 - 18 T is noted. Remarkably, the field dependence of the magnetoresistance (∆ρ(B)/ρ(0)) is neither quadratic nor linear in B. Instead, ∆ρ(B)/ρ(0) is a sublinear concave function of B. Furthermore, even in the sub-kelvin range and field up to 18 T, ∆ρ(B)/ρ(0) does not saturate. The Seebeck coefficient increases from ~5mV/K at 600 mK to about 35 mV/K around room temperature following an S~T1/2 behavior. The implication of these results will be discussed. |
Tuesday, March 15, 2022 8:24AM - 8:36AM |
F12.00003: Second Harmonic Dipoles in Chiral Wide-Gap Insulator Models Andrew Smith, Chong Wang, Di Xiao
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Tuesday, March 15, 2022 8:36AM - 8:48AM |
F12.00004: Probing Phonon Polaritons in Boron Nitride Nanotubes with Thermal Emission Spectroscopy Xueji Wang, Ryan Starko-Bowes, Zhujing Xu, Sandipan Pramanik, Na Lu, Tongcang Li, Zubin Jacob In polaritonic dielectric materials, optically active phonons cause the coupling between electromagnetic waves and the vibrational motions of the polar lattice, leading to phonon polaritons, coupled oscillations of light and matter. Thermally exciting such materials leads to strong fluctuating optical dipole moments and unique thermal emission characteristics in well-defined spectral regions. Hexagonal boron nitride (hBN) is an emerging 2D material that possesses high-frequency and low-loss optical phonons in two spectrally distinct mid-infrared frequency bands. The hyperbolic nature of these frequency bands leads to a large local density of states (LDOS). However, in 2D form, the polaritonic states are dark modes, bound to the material. In this study, by exploiting the cylindrical form of hBN, i.e. boron nitride nanotubes (BNNTs), we create subwavelength particles capable of coupling these dark modes to radiative ones. Through direct measurement of thermal emission of a disordered system of BNNTs, we confirm their radiative polaritonic modes and show that the antenna behavior can be observed even in a disordered system. |
Tuesday, March 15, 2022 8:48AM - 9:00AM |
F12.00005: Infrared Spectroscopy and DFT Calculations of Electronic and Lattice Vibrational Properties in FeGa3 Catalin Martin, Vladimir Martinez, Petar Mitric, Darko Tanaskovic, Rodica M Martin, Ihor Sydoryk, David B Tanner, Weijun Ren, Cedomir Petrovic The intermetallic Fe-based semiconductors FeSb2, FeSi and FeGa3 distinguish themselves because of reports of Seebeck coefficients in excess of 10,000 μV/K. However, there is not yet a clear consensus on the origin of such strong thermoelectric effect in these compounds and two main scenarios are invoked: the phonon-drag effect, due to a strong coupling of lattice vibrations to the mobile charges, and electron-electron correlations, manifested in the band structure, magnetic and electrical transport properties. Here we address some of these questions in FeGa3 by means of combined experimental measurements of infrared reflectance and Density Functional Theory (DFT) calculations. Optical band gap determined experimentally is confirmed by the theoretical values, and most noticeably, there is remarkable agreement between the observed phonon frequencies and the density functional perturbation theory (DFPT) calculations. We will discuss further the evolution of the spectral weight with temperature and the structure of the vibrational modes, as well as their potential implications on the large Seebeck coefficient in FeGa3. |
Tuesday, March 15, 2022 9:00AM - 9:12AM |
F12.00006: Fermi edge singularity in ultracold electron-hole plasma Erik A Szwed, Darius J Choksy, Leonid V Butov, Kirk Baldwin, Loren N Pfeiffer We study ultracold neutral electron-hole plasma in separated electron and hole layers in GaAs/AlGaAs coupled quantum well heterostructures. The long electron-hole recombination lifetimes, due to the spatial separation between the electron and hole layers, allows the plasma to cool to low temperatures. We observe a strong enhancement of the photoluminescence intensity at the Fermi energy of the ultracold plasma, evidence of the emergence of the excitonic Fermi edge singularity. This enhancement vanishes with increasing temperature. We control the electron-hole density by the laser excitation power, and with the increasing electron-hole density, observe a transition from the ultracold gas of spatially indirect excitons, the hydrogen-like bound pairs of separated electrons and holes, at low electron-hole densities to the ultracold plasma with the Fermi edge singularity at high electron-hole densities. |
Tuesday, March 15, 2022 9:12AM - 9:24AM |
F12.00007: Thermal Expansion Coefficient of Silicon Nanoparticles with Nanometer Resolution Bibash Sapkota, Serdar Ogut, Robert F Klie With the size of electronic devices becoming increasingly smaller, it has become important to understand thermal expansion coefficients (TECs) and thermal properties of materials, particularly at interfaces, on the sub-nanometer scale. However, traditional techniques, such as scanning thermal microscopy or Raman thermometry are limited in spatial resolution due to mechanical constraints or optical diffraction limit. According to the free electron model, the plasmon resonance energy of a material is related to the temperature through its electron density. Using this property, several studies have shown that nanoparticles, such as Al or Si, can be used as nanothermometers to measure the local temperature with high resolution and high accuracy. |
Tuesday, March 15, 2022 9:24AM - 9:36AM |
F12.00008: Temperature Response of the Optical Properties of Ultra-Wide Bandgap β-Ga2O3 Films Jeffrey Lapp, Dinesh Thapa, Isiaka Lukman, Leah Bergman β-Ga2O3 is a semiconductor with ultra-wide bandgap at ~ 5 eV that is thermodynamically stable up to 1800 C which enables its application in high temperature devices. This research focuses on the temperature response of the bandgap and the UV photoluminescence (PL) at 77 K to 620 K. β-Ga2O3 films were grown using a sputtering technique and analyzed via transmission, Raman scattering, and UV- PL. The bandgap exhibited a redshift ~ 200 meV as a function of temperature; its room temperature value is 4.85 eV. The electron-phonon interaction model pointed to a low energy phonon, ~ 31 meV, that is involved in the thermal properties of the bandgap. Urbach analysis indicated that defects are the dominant mechanism controlling the band edge characteristics even at elevated temperatures where phonon dominance is usually expected. Defects are attributed to the disordered forms of graphite that were detected via Raman scattering, and to the granular morphology of the film. A deep-UV laser with an above-bandgap exaction was employed to map the PL. The highly resolved spectra show a strong emission ~ 3.56 eV attributed to self-trapped holes (STH) that exhibited a weak temperature dependance thus implying a strong localization. A low intensity PL was found at 4.85 eV that agrees with the value of the bandgap and is attributed to free e-h recombination whose intensity is impeded by the STH. |
Tuesday, March 15, 2022 9:36AM - 9:48AM |
F12.00009: Phonon-Assisted Ballistic Current from First-Principles Calculations Zhenbang Dai, Aaron Schankler, Lingyuan Gao, Liang Tan, Andrew M Rappe The bulk photovoltaic effect (BPVE) refers to current generation due to illumination by light in a homogeneous bulk material lacking inversion symmetry. In addition to the intensively studied shift current, the ballistic current, which originates from asymmetric carrier generation due to scattering processes, also constitutes an important contribution to the overall kinetic model of the BPVE. In this work, we use a perturbative approach to derive a formula for the ballistic current resulting from the intrinsic electron-phonon scattering in a form amenable to first-principles calculation. We then implement the theory and calculate the ballistic current of the prototypical BPVE material BaTiO3 using quantum-mechanical density functional theory. The magnitude of the ballistic current is comparable to that of the shift current, and the total spectrum (shift plus ballistic) agrees well with the experimentally measured photocurrents. Furthermore, we show that the ballistic current is sensitive to structural change, which could benefit future photovoltaic materials design. |
Tuesday, March 15, 2022 9:48AM - 10:00AM |
F12.00010: Time Resolved Carrier Dynamics in Ge Based Heterostructures Grown on GaAs Substrate Brenden A Magill, Rathsara R Herath Mudiyanselage, Yannick Pleimling, Nicholas W Smith, Christopher J Stanton, Mantu K Hudait, Giti A Khodaparast
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Tuesday, March 15, 2022 10:00AM - 10:12AM |
F12.00011: Probing spatial heterogeneity in exciton and carrier diffusion using transient holographic microscopy Franco V Camargo, Martin Hörmann, Federico Visentin, Niek F van Hulst, Matz Liebel, Giulio Cerullo Ultrafast transient microscopic techniques have been used for several years to study exciton and carrier diffusion in materials, down to ultrafast timescales. A common issue remains that all such experiments rely on observing diffusion around a single diffraction-limited spot of the sample, raising the question of how representative the results may be, particularly in samples that are prone to spatial heterogeneity such as polycrystalline thin films, bulk-heterojunctions or 2D materials. The main issue to perform transient techniques in a wide-field configuration is that the slow acquisition speed of cameras limits the modulation frequency of the excitation beam, rendering shot-to-shot signal demodulation impossible even at rather low repetition rates. Here we show how to overcome this issue using a transient holographic microscope that decouples the modulation frequency of the pump beam from the camera acquisition speed, allowing us to obtain ultrafast transient images of the sample covering areas of around 100x100 micrometers. We will demonstrate how to use this to simultaneously acquire diffusion data around over 100 evenly spaced points across the entire field of view, hence obtaining significant statistical information of the sample in a single measurement. |
Tuesday, March 15, 2022 10:12AM - 10:24AM |
F12.00012: The inelastic light scattering of crystals at finite temperatures and the correct tensor to describe it Nimrod Benshalom, Olle Hellman, Omer Yaffe The microscopic manifestation of temperature in lattice dynamics is generally understood through the harmonic approximation, where atomic motion is mapped onto a set of vibrational normal modes (i.e., phonons). Modern studies into lattice dynamics of solids significantly expand on this view to account for anharmonic phenomena such a thermal expansion and phase transitions. In contrast, studies into the electronic properties of solids rarely go beyond a quasi-harmonic treatment. |
Tuesday, March 15, 2022 10:24AM - 10:36AM |
F12.00013: Electric-controlled thermal transistor based on Janus monolayer MoSSe Donghai Wei With the rapid emergence of the high-power-density intelligent terminals, the excellent thermal management in nanostructures, especially for semiconductors, will undoubtedly have significant impact on modern life. However, current thermal management components, especially for the temperature control components, such as thermal diodes, thermal transistors, thermal logic gates, etc., are still suffering from the poor stability, adjustability, time efficiency and difficulty in implementation. Here, we comprehensively investigate the electric-controlled thermal transistor (ECTT) driven by electric field instead of temperature applied in the Janus monolayer MoSSe by employing the first-principles calculations. The result shows that the heat flow amplification coefficient measured by the thermal conductivity is 2.13 times higher than the pristine one under the electric field of 0.040 VÅ-1. The underlying mechanism revealed by electronic structures shows that the interactions between electrons and phonons are renormalized resulting from the tremendous charge density redistribution caused by the external electric field, and ultimately modulate the phonon anharmonicity. The ECTT component will provide new inspiration for thermal management and information processing in the future. |
Tuesday, March 15, 2022 10:36AM - 10:48AM |
F12.00014: Investigation of the β to β' Resistivity Anomaly in the Chalcogenide As2Te3 JEREMY P DION, Maureen Reedyk The chalcogenides are a family of layered compounds that exhibit interesting properties. As2Te3 is a chalcogenide that has α, β and β' polymorphic phases. Metallic β-As2Te3 is a metastable phase[1] that, below a temperature of ≈ 200K, undergoes a structural phase transition to β'-As2Te3. Within the region of this transition a strong signature can be detected in the resistivity beyond which it resumes a metallic behaviour[1]. We have employed a phenomenological fit on the resistivity of the β and β' phases of As2Te3 to better characterize the nature of this transition. Most notable is the occurrence of cross-transition invariance in the slope of the resistivity, a topic of considerable interest in other materials[2]. The direct strength of the β-As2Te3 to β'-As2Te3 transition as well as the width of the transition can be modelled using this approach. Drude-Lorentz fits to temperature-dependent infrared reflectivity data of the β and β' phases will be discussed to aid in the analysis of the resistivity and provide context on the mechanisms driving the electronic properties in the system. |
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