Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F27: Electronic Structure: Theory & Spectra |
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Sponsoring Units: FIAP Chair: Maicol Ochoa, National Institute of Standards and Technology Room: 404 |
Tuesday, March 3, 2020 8:00AM - 8:12AM |
F27.00001: Extracting Electron Densities in n-Type GaAs from Raman Spectra. Maicol Ochoa, James E Maslar, Herbert S. Bennett Raman measurements can be utilized as a non-destructive method for determining carrier density in compound semiconductors. Rigorous determination of carrier density involves comparing measured and simulated coupled phonon-plasmon Raman spectra. Theories of varying degrees of complexity have been employed for simulating spectra in which spectra are generated as a function of Fermi energy (or carrier density in the degenerate limit). In general, previously utilized spectral models are strictly valid only for a temperature near 0 K and either for the classical or degenerate doping limit. However, such models cannot necessarily capture all spectral information. To overcome this limitation, we have developed a model that is valid at any temperature, any doping level, and for arbitrary values of the ratio Q2/α (where Q is the magnitude of the normalized wavevector, and α is the normalized frequency used in the Raman measurements). We compare measured n-type GaAs spectra, obtained from epilayers with different carrier concentrations, with simulated spectra obtained with this new spectral model employing different descriptions of the band structure as a function of Fermi energy. |
Tuesday, March 3, 2020 8:12AM - 8:24AM |
F27.00002: Microscopic perspective on the magnetoelectric response of an insulator Perry Mahon, John Edward Sipe We implement a microscopic theory of polarization and magnetization to calculate the magnetoelectric response of an insulator at zero temperature. To first order in the applied fields the free charge and current densities vanish, and as a consequence the response of the system is characterized by the first-order corrections to the microscopic polarization and magnetization fields arising from the applied electric and magnetic fields. Associated with the dipole moment of the microscopic polarization (magnetization) field is a macroscopic polarization (magnetization), for which we extract various response tensors. The magnetoelectric tensor is composed of two distinct parts: the Chern-Simons and cross-gap contributions. We compare our results for these with those of earlier work. We analyze the origin of both the Chern-Simons and cross-gap terms from the perspective of our microscopic theory, and find the former to arise from more “localized” contributions to the response, while the latter to arise from more “extended” contributions. |
Tuesday, March 3, 2020 8:24AM - 8:36AM |
F27.00003: Accurate, Ground State Electronic and Transport Properties of h- BN Yuriy Malozovsky, Cheik Bamba, Anthony Stewart, Lashounda T Franklin, Diola Bagayoko We present an ab-initio, density functional theory (DFT) description of ground state electronic and related properties of hexagonal boron nitride (h-BN). We used a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) formalism.We implemented the Bagayoko, Zhao, and Williams method, as enhanced by Ekuma and Franklin (BZW-EF). The method leads to the ground state of the material, in verifiable manner, without employing over-complete basis sets. Consequently, our results possess the full, physical content of DFT, as per the second DFT theorem [AIP Advances, 4, 127104 (2014)]. We report the ground state band structure, band gap, total and partial densities of states, and electron and holes effective masses. Our calculated, indirect band gap of 4.3 eV is in excellent agreement with the measured value. The valence band maximum is slightly to the left of the K point, while the conduction band minimum is at the M point. Our calculated total width of the valence, total and partial densities of states are in agreement with corresponding, experimental findings. |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F27.00004: Electronic structure of p-type transparent conducting oxide CuAlO2 Mohamed Salah, Joonseok Yoon, Xiaosong Liu, Wanli Yang, Bongjin Simon Mun, Mohamed Mahmoud El-Desoky, Zahid Hussain, Honglyoul Ju, Sung-Kwan Mo Transparent Conducting Oxides (TCOs) are generally considered to be very distinctive material because of their combining of electrical conductivity with the visible light transmission in a single material. The delafossite oxide CuAlO2 is a p-type TCO which can be used to fabricate transparent p–n junction from TCO materials. In this work, we combine angle-resolved photoemission spectroscopy (ARPES) and X-ray emission and absorption spectroscopies (XES & XAS), to visualize the low-energy electronic structure. Fermi surface topology, detailed band structure, the effective mass of valence electrons, and the band gap size of the single crystal CuAlO2 were examined experimentally. The electronic structure obtained from ARPES measurements are compared with theoretical calculations. These results indicate that CuAlO2 is a good p-type TCO that may serve as a platform for optoelectronic applications. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F27.00005: A higher-dimensional electronic superstructure in a misfit chalcogenide (PbSe)1.16(TiSe2)2 Yuhki Kohsaka, Teppei Ueno, Tadashi Machida, Tetsuo Hanaguri, Jun Akimitsu, Kaya Kobayashi Aperiodic crystals, despite lack of translational invariance, are characterized by the primitive vectors as periodic crystals. A characteristic of aperiodic ones is number of the primitive vectors, which is larger than the physical dimension. This represents higher-dimensional nature of aperiodic crystals, resulting in exotic phenomena in atomic quasicrystals, light, and ultracold atom. However, no higher-dimensional phenomena have been found in electronic matters, where inner degrees of freedom and strong correlation are involved to yield rich phenomena. Here we show a higher-dimensional electronic modulation in a misfit chalcogenide (PbSe)1.16(TiSe2)2 with spectroscopic imaging scanning tunneling microscopy. We find that the local density-of-states exhibits an aperiodic superstructure while the periodic charge density wave of 1T-TiSe2 is completely suppressed. Our finding demonstrates that the interplay between hexagonal and tetragonal sublattices provides the electronic matters with extra degrees of freedom from higher dimensions and higher-dimensional electronic properties can be explored in a wider range of materials including artificial heterostructures. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F27.00006: Experimental Observation of Hidden Berry Curvature in Inversion-Symmetric Bulk 2H-WSe2 Soohyun Cho, Seung Ryong Park We investigate the hidden Berry curvature in bulk 2H-WSe2 by utilizing the surface sensitivity of angle resolved photoemission (ARPES). The symmetry in the electronic structure of transition metal dichalcogenides is used to uniquely determine the local orbital angular momentum (OAM) contribution to the circular dichroism (CD) in ARPES. The extracted CD signals for the K and K' valleys are almost identical, but their signs, which should be determined by the valley index, are opposite. In addition, the sign is found to be the same for the two spin-split bands, indicating that it is independent of spin state. These observed CD behaviors are what are expected from Berry curvature of a monolayer of WSe2. In order to see if CD-ARPES is indeed representative of hidden Berry curvature within a layer, we use tight binding analysis as well as density functional calculation to calculate the Berry curvature and local OAM of a monolayer WSe2.We find that measured CD-ARPES is approximately proportional to the calculated Berry curvature as well as local OAM, further supporting our interpretation. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F27.00007: Theoretical study on symmetries and properties of three-dimensional valleytronic systems Manabu Takeichi, Shuichi Murakami Materials with spin-split valleys showing direct bandgaps, such as transition metal dichalcogenides, have been attracting interest in the context of valleytronics. All such materials known so far are two-dimensional. In this talk, we show a list of space groups to realize three-dimensional materials with such a valley degree of freedom. For this purpose, we made some criteria for space groups allowing valleys with good properties for valleytronics, and we find that there are only a few space groups that satisfy all of these criteria. Moreover, we propose a model which possesses inequivalent six valleys, and reveal its properties in the context of valleytronics, such as spin-valley coupling, nonzero Berry curvature, and some ways of controlling these valleys. |
Tuesday, March 3, 2020 9:24AM - 9:36AM |
F27.00008: Atomic and Electronic Structure of the Edges of multilayer and Monolayer Tin disulfide (SnS2) Tao Yan Because of its two-dimensional structure and semiconducting properties, tin disulfide (SnS2) is of interest for applications in electrochemical catalysis and sensing, as an electron transport layer for photovoltaics, and as an active material in photodetectors and thin film transistors. While the atomic and electronic structure of the basal planes of bulk and monolayer SnS2 are well known, the same is not known for the edges, which could have a major influence on the performance of SnS2 in the aforementioned applications. This paper reports on density functional theory (DFT) simulations and experimental measurements of the atomic and electronic structure of the edges of multilayer and monolayer SnS2 under different chemical conditions. We found that the band gap of the SnS2 edges becomes smaller with increasing sulfur coverage, and thereby determined the influence of chemical synthesis conditions on the electronic structure of the edges. We also found that as-synthesized SnS2 has unpaired electrons at the edges, which suggests a direction to solve the degradation issue of SnS2 as a catalyst in aqueous electrolytes. |
Tuesday, March 3, 2020 9:36AM - 9:48AM |
F27.00009: Theoretical and experimental measurements for the (Eu1-xScx)2Zr2O7 Zirconate pyrochlore Mourad Boujnah, Elizabeth Chavira, Carlos Quintanar, Mohamed Abatal, Antonio Fernandez Fuentes The interest to study pyrochlores was the diver’s optical, electric and magnetic properties. Theoretical work was done by using density functional theory (DFT). We studied the electronic properties to see the effect of Scandium in Eu2Zr2O7 for several percentage of Sc doping in the Zirconate pyrochlore and we see that we shift from half metal with an important magnetic moment to predicting semiconductor with 2.8 eV as band gap. Moreover, we observed that these doping present a significant coefficient absorption and transmission in the visible range which are around 10x104 cm-1 and 88 % respectively. To understand that we calculated the electrical properties. For the experimental results, when x = (0, 0.5 and 1) we observed by thermal analysis an interesting behavior in air. Generally gone mass and exhibits exothermic and endothermic conduct. Each thermal change, it is analysed with X-ray powder diffraction also the reagents. We detected a substitutional solid solution with complex mechanism, in air and oxygen flux. Summary, ZrO unit cell accept oxygen and exist cationic substitution in Sc and Eu ions. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F27.00010: ACCURATE, SELF – CONSISTENT DENSITY FUNCTIONAL THEORY DESCRIPTION OF ROCK-SALT MAGNESIUM SELENIDE (MgSe) Blaise Ayirizia, Uttam Bhandari, Yuriy Malozovsky, Lashounda T Franklin, Diola Bagayoko We report comprehensive results from density functional theory (DFT) calculations of electronic, transport, and bulk properties of magnesium selenide (MgSe) in the rock-salt crystal structure. We used 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 attain the ground state of the material. Therefore, our results possess the full physical content of DFT. With a room temperature lattice constant of 5.460Å, our calculated, indirect band gap is 2.49 eV. We present the ground state band structure and the total (DOS) and partial (pDOS) densities of states. Our results are practically in agreement with available, corresponding experimental data and with some previous, theoretical findings. We found a value of 63.1GPa for the bulk modulus, in excellent agreement with the experimentally determined 62.8 ±1.6 GPa. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F27.00011: First principle investigation of electronic, transport, and bulk properties of zinc-blende magnesium sulfide (MgS) Uttam Bhandari, Blaise Ayirizia, Yuriy Malozovsky, Lashounda T Franklin, Diola Bagayoko We have studied the electronic, structural, and transport properties of the zinc-blende magnesium sulfide (zb-MgS), using Density Functional Theory (DFT). We employed a Local Density Approximation (LDA) potential with a Linear Combination of Atomic Orbitals (LCAO) approach. Our computational method leads to the ground state of the materials without utilizing over-complete basis sets. The calculated direct band gap of zb-MgS is 4.43 eV, in excellent agreement with the experimental band gap of 4.45 ± 0.2 eV. We also report the total and partial densities of states, the electron effective masses, the equilibrium lattice constant, and the bulk modulus. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F27.00012: Towards a Th-229 Nuclear Clock: Measurements of the Bandgap of ThF4 by Electron Spectroscopy Techniques Roberto Caciuffo, Thomas Gouder, Rachel Eloirdi, Mikhail Osipenko, Mauro Giovannini, Richard L. Martin The existence of an excited nuclear state at about 8.3 eV in Th-229 has stimulated enormous interest, because it opens the possibility to develop solid-state optical nuclear clocks with unparalleled accuracy and stability. In such a device, Th-229 should be embedded in a crystalline matrix with a band gap larger than the isomer energy, in order to suppress decay by internal conversion. The crystal matrix should also be able to host Th-229 atoms in regular lattice positions, in order to minimize color center defects. Here, we present an experimental determination of the bandgap of ThF4 performed by two different techniques. The first one is based on a combination of x-ray photoemission spectroscopy and bremsstrahlung isochromat spectroscopy. The second measurement exploited the position of the inelastic threshold in reflection electron energy loss spectroscopy. Both measurements gave compatible values of the bandgap, with the average ΔE = 10.2(2) eV [1]. This value is in excellent agreement with theoretical calculations. The measured bandgap is significantly larger than the 229mTh excitation energy making ThF4 a possible candidate material for a solid-state nuclear clock based on the vacuum ultraviolet γ decay. |
Tuesday, March 3, 2020 10:24AM - 10:36AM |
F27.00013: Analysis of pre-edge of oxygen K-edge X-ray absorption spectra of transition metal oxides Ruimin Qiao, Subhayan Roychoudhury, David Prendergast, Wanli Yang The recently developed MBXAS[1] formalism is a powerful tool for inexpensive, accurate simulation of X-ray absorption spectroscopy (XAS). By approximating the final (initial) many-body state as a Slater determinant of all electronic orbitals obtained in presence (absence) of the core hole, one can accurately simulate the electronic relaxation resulting from core-excitation, while maintaining computational advantage by staying within a mean-field framework, such as density functional theory (DFT). In collaboration with experimentalists, we used MBXAS to simulate the oxygen-K edge XAS of 3-d transition metal oxides (TMO). The onset-energy of each spectrum is determined from total energy differences of ground and excited state DFT calculations. For a given transition-metal, the first O K-edge pre-peak energy decreases with increasing valence, indicating strong contribution of metal 3-d levels in the conduction band edge via hybridization. Unlike transition-metal L-edge spectra, which are dominated by local atomic ligand field effects, the O K-edge essentially maps the conduction bands. The oxygen-K edge offers us an opportunity to plot the first-peak positions of all TMOs with a common energy scale. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F27.00014: A detailed Raman study of the photochemical oxidation process of monolayer CVD grown graphene MOHD MUSAIB HAIDARI, Jin Hong Kim, Jin Sik Choi Although graphene oxide (GO) has emerged as a promising material in the semiconductor industry, optimization of oxidation conditions to meet industrial needs had remained a challenge for researchers. We prepared a monolayer GO sheet by photochemical treatment of CVD graphene within 80 s using UV irradiation. TEM data confirms that there were no structural defects through the optimized oxidation condition with 20% oxygen content. Comparing to conventional GO flakes, this large area GO layer shows higher homogeneity in functional group distribution. Comparison of Amplitude and Area intensity ratios of Raman peaks and XPS data show a correlation between changes in D’ (~1620 cm-1), G (~1587 cm-1), and 2D (~2678 cm-1) peaks with C sp3 (C-O), epoxide (C-O-C), and C sp2 (C=C) bonding. Moreover, although patterned graphene and GO regions are imperceptible by optical illuminance, they are distinguishable by Raman D and/or G-peak mapping. According to AFM data, our GO samples show the average thickness of 0.79 nm in its optimized condition with an ultra-clean surface comparable to that of exfoliated graphene. This work reveals some details about the oxidation process of graphene and sets the ground for transparent flexible optical and electrical applications of functionalized graphene. |
Tuesday, March 3, 2020 10:48AM - 11:00AM |
F27.00015: Realization of BaZrS3 chalcogenide perovskite thin films for optoelectronics Xiucheng Wei, Haolei Hui, Mengjiao Han, Samanthe Perera, Junhao Lin, Yi-Yang Sun, Shengbai Zhang, Hao Zeng BaZrS3, a prototypical chalcogenide perovskite, has not yet been deeply explored despite being first synthesized in the mid-1950s. In recent years, several publications on powder samples reveal that BaZrS3 has a direct band gap of 1.7 to 1.8 eV, a high stability against moisture and pressure, and a very strong interaction with light. However, many of the fundamental properties still remain unknown due to the lack of film samples. Here we report the fabrication of BaZrS3 thin films, by sulfurization of corresponding BaZrO3 films deposited by pulsed laser deposition. Transport measurements indicate the films are n-type semiconductors with carrier densities in the range of 1019 to 1020 cm-3. The hall mobility ranges from 2.1 to 13.7 cm2/Vs depending on the sulfurization temperature. UV-Vis result shows an absorption coefficient of >105 cm-1 at a photon energy of >1.97eV and temperature dependent conductivity measurements reveal shallow donor level with an activation energy of several milli-electron volts. Our results assure that BaZrS3 is a promising candidate material for optoelectronics. |
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