Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D52: Electronic Structure: Thermodynamic and Optical PropertiesIndustrial
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Sponsoring Units: FIAP Chair: Daniel Jost, Stanford University Room: Room 308 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D52.00001: A size-consistent Gruneisen-quasiharmonic approach for lattice thermal conductivity Chee Kwan Gan We present a size-consistent Gruneisen-quasiharmonic approach (GQA)[1] for the calculation of the lattice thermal conductivity, which |
Monday, March 6, 2023 3:12PM - 3:24PM |
D52.00002: (TaSe4)3I: Reconciling transport, optics and ARPES Irián Sánchez Ramírez, Claudia Felser, Maia Garcia Vergniory, Fernando De Juan Recently, the quasi one-dimensional transition metal tetrachalcogenide (TaSe4)3 I has been found to display the coexistence between superconductivity and ferromagnetism. This result is conflicted with the previous works on this material, which overall predict it to be insulating. Furthermore, no consensus exist on the electronic properties of (TaSe4)3I in the literature, since ARPES and transport measurements disagree by an order of magnitude on its electronic bandgap. In this work, we rationalize the observed transport gaps and reconcile them with ARPES and optical experiments by relating the dissimilarities with band-folding due to an approximated translational symmetry due to distortion caused by Se cages. Finally, we relate the observed superconducting behavior to a possible extrinsic hole doping which can tune the Fermi level through a Van Hove singularity. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D52.00003: Engineering Flat Bands in InAs/GaSb Quad-layer Quantum Well Structures Wei-Chen Wang, Jiyuan Fang, Zachery Enderson, Zhigang Jiang, Yuxuan Jiang, Li Xiang, Mykhaylo Ozerov, Dmitry Smirnov, Samuel D Hawkins, John Klem, Aaron J Muhowski, Wei Pan Previous studies have shown that adjusting the relative thickness of InAs/GaSb double quantum wells (QWs) can transform the system from a semiconductor to a semimetal and create a dispersionless conduction band due to strong electron-hole wavefunction mixing. In our studies using k•p band structure calculations, we explore the potential to engineer flat bands in InAs/GaSb quad-layer QW materials. Using realistic band parameters and considering strain effects, our calculations show that nearly dispersionless bands can occur in specific parameter space windows. We investigate the validity of these predictions experimentally by probing the band structures of quad-layer QWs grown via molecular-beam epitaxy with magneto-infrared spectroscopy and magneto-transport. The Landau level transitions observed in this experiment can be directly compared to the optical conductivity calculated using the eight-band k•p model. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D52.00004: Mapping of Extended Hubbard Interactions to GW Self-Energy Minjae Kim We present a mapping from the extended Hubbard interactions to the local and non-local static self-energy of the GW approximation. Thanks to the mapping and the proper treatment of position-dependent screening of charge for the Hubbard interactions, we show that the recently developed self-consistent pseudohybrid functional method for the on-site (U) and inter-site (V) Hubbard interactions within the density functional theory (DFT+U+V) is an efficient and accurate method for descriptions of various physical properties of solids. We provide several examples proving the relevance of this method for descriptions of dielectric screenings of solids, (i) quasiparticle band gaps, effective mass, and absorption spectra of covalent semiconductors, silicon (3 dimensional) and monolayer black phosphorus (2 dimensional), and (ii) optical phonon frequency of a correlated insulator, NiO. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D52.00005: Electronic structure of ß-Ga2O3 as seen via measured and calculated resonant inelastic soft x-ray scattering John Vinson, Elizaveta Pyatenko, Dirk Hauschild, Clemens Heske, Lothar Weinhardt Transparent conductive oxides (TCOs) are a vital component in a wide variety of technologically important materials such as photovoltaics or light emitting diodes with a rare combination of properties: transparency and electrical conductivity. Improving these materials by reducing absorption while increasing carrier mobility requires an increased understanding of their electronic structure. Resonant inelastic x-ray scattering (RIXS) provides a bulk-sensitive probe of both valence and conduction bands. Here, we demonstrate the suitability of RIXS at the oxygen K edge for examining the electronic structure of TCOs using the example of pristine ß-Ga2O3. We compare experimental RIXS maps with those calculated using the Bethe-Salpeter equation (BSE) method within the OCEAN code. We find that the BSE calculations are able to capture all main features of the measured spectra correctly. Controlling the incoming x-ray polarization with respect to the crystallographic axes allows selective excitation of different regions within the band structure, which gives a clear signature in both experimental and theoretical spectra. |
Monday, March 6, 2023 4:00PM - 4:12PM Author not Attending |
D52.00006: Electronic states in semiconductor truncated ellipsoidal quantum dots Karen Dvoyan, Abdennaseur Karoui, Branislav Vlahovic Electronic states in a GaAs truncated ellipsoidal quantum dot (QD) are theoretically investigated within the framework of the geometric adiabatic approximation both in the strong and weak quantum confinement regimes. For the lower levels of the spectrum, the localization of the electron in the vicinity of the QD center-of-gravity is proved. Lowering the QD ellipsoidal symmetry leads to the appearance of an atypical linear term in the effective confining potential. For the weak quantum confinement regime, the motion of the exciton's center-of-gravity is quantized, which leads to the appearance of additional Coulomb sub-levels. The corresponding selection rules of quantum transitions for the interband absorption of light are obtained. The absorption threshold behavior characteristics depending on the QDs geometrical sizes are also revealed. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D52.00007: Higher order effective coefficients in Ge/Si core/shell nanowire devices Sebastian Miles Germanium based nanowires are prominent platforms in mesoscopic physics because of their tunable spin-orbit interaction. This property makes them an interesting candidate for hole-qubit devices or as a platform for Majoranas. Hence, a good understanding of effective models for the relevant degrees of freedom in these devices is of great importance. We revisit the subject of effective Hamiltonians and effective coefficients for efficient nano-device control in Ge/Si core/shell semiconductor nanowires from a perturbation theory perspective. We elaborate on relevant terms and present numerical and semi-analytical results of Löwdin perturbation theory to second order. We discuss the consequences of higher order terms on the effective models of interest for device applications. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D52.00008: Ab-initio Calculations of Electronic Properties of Bulk and 2D Molybdenum Disulfide (MoS2) YURIY MALOZOVSKY, Diola Bagayoko We present results from ab-initio, self-consistent density functional theory (DFT) calculations of electronic properties of molybdenum disulfide (MoS2), for the bulk and a 2D sample. The bulk MoS2 (2H-MoS2) is in the hexagonal structure with the space group P63/mmc and Pearson symbol hP6 (#194); the 2D sample is also in the hexagonal structure with the space group P-3m1. We utilized a local density approximation (LDA) potential and the linear combination of atomic orbital (LCAO) formalism. Our calculations performed a generalized minimization of the energy to reach the ground state, as required by the second DFT theorem. This process ensures the full, physical content of our findings that include electronic energy bands, total and partial densities of states, and electron and hole effective masses. Our calculated band gap for room temperature lattice constants of a= 3.16 Å and c=12.294 Å is 1.42 eV, for the bulk, and is indirect; it is 2.65 eV for the 2D samples, for lattice constants of a= 3.187 Å and c=31.87 Å, and is a direct band gap. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D52.00009: Ab-initio Density Functional Theory Description of Rock-Salt Magnesium Selenide (MgSe) YURIY MALOZOVSKY, Blaise Awola Ayirizia, Uttam Bhandari, Lashounda Franklin, Diola Bagayoko We report comprehensive results from density functional theory (DFT) calculations of electronic, transport, and bulk properties of rock-salt magnesium selenide (MgSe). We utilized a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) method. We performed a generalized minimization of the energy using successive, self-consistent calculations with augmented basis sets. We verifiably attained the ground state of the material. Therefore, our results possess the full physical content of DFT. Our calculated, indirect bandgap is 2.49 eV for a room temperature lattice constant of 5.460Å. We present the ground-state band structure and the total and partial densities of states, DOS and PDOS, respectively. Electron and hole effective masses were calculated for the material. Results are discussed and shown to be in reasonable agreement with available experimental data. Our calculated bulk modulus of 63.1 GPa is in excellent agreement with the experimental value of 62.8 ± 1.6 GPa. Our predicted equilibrium lattice constant, at zero temperature, is 5.424Å with a corresponding indirect bandgap of 2.51 eV. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D52.00010: First Principle Calculations of Ground State Electronic, Transport, and Structural Properties of zinc-blende beryllium sulfide (zb-BeS) YURIY MALOZOVSKY, Janee Brumfield, Blaise Awola Ayirizia, Diola Bagayoko We have studied the electronic, structural, and transport properties of the zinc-blende beryllium sulfide (zb-BeS), using density functional theory (DFT). We employed a Local Density Approximation (LDA) potential and the Linear Combination of Atomic Orbitals (LCAO). Our computational method leads to the ground state of the materials without utilizing over-complete basis sets. Our calculated, indirect band gap is 5.44 eV, from ? to a conduction band minimum between ? and X, for a room temperature lattice constant of 4.863 Å, is in excellent agreement with experiment which indicates the lower limit of 5.5 eV for the indirect band gap. We also report the total (DOS) and partial densities of states (pDOS), electron and holes effective masses, the equilibrium lattice constant, and the bulk modulus. Our calculated bulk modulus of 107.7 GPa is in excellent agreement with experiment (105 GPa). Our predicted equilibrium lattice constant at zero temperature is 4.814 Å. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D52.00011: Strain-enhanced radiative recombination in lonsdaleite Ge Christopher A Broderick, Xie Zhang, Mark E Turiansky, Chris G Van de Walle Growth of conventional semiconductor materials in metastable crystal phases presents rich new opportunities to engineer electronic band structure. Experimental demonstration of direct-gap-like optical emission from lonsdaleite Ge (2H-Ge) is attracting significant attention as a route to a direct-gap material for Si photonics applications [1]. The 2H-Ge direct band gap originates via back-folding of the L-point conduction band minimum of conventional, indirect-gap diamond-structured Ge (3C-Ge). This “pseudo-direct” band gap has theoretically predicted low oscillator strength [2], in stark contrast to a high experimentally inferred radiative recombination coefficient B comparable to that conventional 3C-InAs [1]. We report first-principles calculations of the B coefficient for 2H-Ge. We find that B in pristine 2H-Ge is at least three orders of magnitude lower than in 3C-InAs. To explain this discrepancy, we explore the impact of strain that could be unintentionally present in 2H-Ge nanowires. We show that [0001] uniaxial tensile stress can drive significant enhancement of B by inducing a pseudo-direct- to direct-gap transition. In the context of experiment, our computed radiative lifetimes suggest as-yet unquantified nonradiative processes that dominate carrier recombination in unstrained 2H-Ge. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D52.00012: Resolving voltage hysteresis in low temperature RF-STM I(V) curves on terminated Si (100) samples Michael Dreyer, Jonathan J Marbey, Robert E Butera Recently, our group has been measuring the voltage dependent tip-sample capacitance CTS(V) using an RF tank circuit on Cl terminated Si (100) samples in a milli Kelvin scanning tunneling microscope (mK-STM). These curves show hysteresis with respect to the voltage sweep direction (forward (+ to -) and backward (- to +)). Alongside, we have been measuring I(Vbias) data which also show a large hysteresis. Notably, both sets of curves show little change with the sweep time within 1 second to 2 minutes but depend on the voltage range of the sweep. As such, the apparent hysteresis can likely be attributed to slow charge motion inside the silicon sample which significantly distorts the actual tip-sample voltage (VTS = s(Vbias)). By constraining the tunnel junction resistance to be fixed, we can construct a voltage scaling function to map the current from the forward sweep onto the backward sweep and vice versa. However, this only removes the relative hysteresis. The global scaling function can be estimated by the mean of sforw and sbackw. Our main application is to align the simultaneously measured CTS(V) curves. The CTS hysteresis remains under the voltage correction and is subject of further study. The scaling method will be described in excruciating detail. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D52.00013: Non-Abelian Berry Phases for Holes Confined in SiGe Two-Dimensional Quantum Well System Tatsuki Tojo, Kyozaburo Takeda By coupling the Bloch equation with the time-dependent Schrödinger equation, we formulate the Berry connection tensor for the non-adiabatic process and then define the non-Abelian Berry phase matrix for the multi-subband system. We apply these results to holes confined in a two-dimensional SiGe quantum well system, where the Rashba field induces structure-inversion-asymmetry and the alternating arrangement of Si and Ge heteroatoms causes the bulk-inversion-asymmetry, resulting in the Rashba and Dresselhaus spin-orbit interaction, respectively. Due to the violence of Stokes' theorem, we calculate the non-Abelian Berry phase matrix for the holes by carrying out the contour integration of the non-Abelian Berry connection tensor faithfully. A comparison of the Abelian and non-Abelian Berry phases reveals that the strong intersubband hybridization around the quasi-degenerate points destroys the adiabatic process. Consequently, the "π"-quantization in the Berry phase against energy is broken at these points. We further explore this non-adiabatic process by analyzing the intersubband transition matrix and decomposing it into quantum logic gates. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D52.00014: Light-induced valley splitting and polarization of exciton-polaron in hole-doped monolayer WSe2 YUEH-CHUN WU, Jun Yan, Kenji Watanabe, Takashi Taniguchi In this study we report light-induced energy splitting in valley exciton-polarons in hole-doped monolayer WSe2 without magnetic field. In contrast to the optical stark effect using ultrashort light pulses, a 1-2 meV energy splitting between valleys is observed with continuous wave (CW) sub-milliwatt circular polarized excitation. We attribute the effect to light-induced valley/spin polarized hole carriers, which subsequently gives rise to valley contrast in energy position and oscillator strength of exciton polarons dressed in intervalley fashion. The picture is supported by optical power and gate dependent photoluminescence where the valley contrasts vanish in small optical power and large electrical doping settings. With the energy splitting and valley polarization information, we further estimate the induced valley-polarized hole density approaching1012 cm-2 and valley-contrast Fermi energy as 10 meV in monolayer WSe2. |
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