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 AA10: Connecting Africa, USA, and the World [CAUW] |
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Chair: Omololu Akin-Ojo, University of Rwanda Room: Virtual Room 10 |
Monday, March 20, 2023 5:00AM - 5:29AM |
AA10.00001: Poster Session Omololu Akin-Ojo Two-minute videos from Researchers in Africa |
Monday, March 20, 2023 5:29AM - 5:42AM |
AA10.00002: Machine Learning for Properties of Materials Ibrahim Isah Machine Learning models for (a) predicting whether a material is an insulator or conductor and (b) predicting the nature (direct/indirect) of band gaps of semiconductors without too much computation are presented. We also present our work on searching for harder materials and materials with very high thermal conductivities using Machine Learning models developed in our collaboration. |
Monday, March 20, 2023 5:42AM - 5:55AM |
AA10.00003: Twisted bilayer graphene under spin pumping reveals its flat bands Sonia Haddad The salient property of the electronic band structure of twisted bilayer graphene (TBG), at the so-called magic angle (MA), is the emergence of flat bands around the charge neutrality point. These bands are associated with the observed superconducting phases and the correlated insulating states near the MA. Scanning tunneling microscopy (STM) and spectroscopy (STS) combined with angle resolved photoemission spectroscopy (ARPES) are usually used to visualize the electronic density of states and the flatness of the band structure of the TGB at the MA. Here, we theoretically propose that spin pumping (SP) can provide direct evidence of the flat bands of TBG. We first derive the continuum model of TBG with spin orbit coupling (SOC) induced by proximity effect by a monolayer of a transition metal dichalcogenide (TMD) aligned with one of the graphene layers of TBG. We then consider a junction between this heterostructure and a ferromagnetic insulator (FI). We show that the Gilbert damping, characterizing the SP effect of such a junction, drops at the MA, which provides evidence of the emergence of the flat band and a possible accurate measurement of the MA. |
Monday, March 20, 2023 5:55AM - 6:08AM |
AA10.00004: Structural and dynamical phase transitions phase transitions of NaNbO3 from first-principles calculations Amisi Safari The crystal structures and phase transitions of NaNbO3 are analyzed with density fonctional theory through generalized gradient spproximation-PBEsol (GGA-PBEsol) and local density approximations (LDA). The phonon dispersion curves from the high-symmetry cubic perovskite phase are reported to have many unstable branches, predisposing to several combinations of phase transitions to various distorted structures. The coupling between the modes and the strain relaxation play a key role in the condensation of the ground state of sodium niobate. The instabilities at R and M points of the first Brillouin zone and along the line T (connecting the M and R points) are very important for stabilizing the low-energy phases. Within the GGA-PBEsol approximation, the ground state is rhombohedral ferroelectric/antiferrodistortive (FE/AFD) R3c, while in LDA it is rather the orthorhombic FE/AFD Pmc21 structure that stabilizes the lowest energy in this compound. In both calculations, there is only a small energy difference between the three lowest-energy phases Pmc21 (FE/AFD[110]), Pbcm (antiferroelectric/AFD), and R3c (FE/AFD[111]), which is a key characteristic of antiferroelectricity. The GGA-PBEsol approach provides more sensible results than the LDA approximation. |
Monday, March 20, 2023 6:08AM - 6:21AM |
AA10.00005: BandGap Size or Band Shape? The Real Determinant of Excellent Thermoelectric Variables Adewumi I Popoola The interest in thermoelectric materials (TMs) have persisted for two obvious reasons. The first is that a large part of almost all energy consumption process is lost in the form of wasted heat and thermoelectric materials are good at converting heat directly to electricity. Secondly, TMs can convert heat to electricity without harmful bye-products. TMs with high efficiency is somewhat difficult to achieve because of the interplay of factors around materials electronic structure. While a material band shape is believed to offer some definite impact on thermoelectric variables, the bandgap size role is not clear. Motivated by these observations, two compounds (BaSrSi and IrBiZr) have been evaluated for optimum hermoelectric application. Despite their comparable bandgap size, the peculiar band shape of IrBiZr gave it an overall superior performance over BaSiSr. To our understanding, these compounds are proposed and investigated for the first time. The results are profound to indicate lesser role for bandgap size in the design and optimization of novel thermoelectric materials. |
Monday, March 20, 2023 6:21AM - 6:34AM |
AA10.00006: Electronic and magnetic properties of FexNi1-x overlayer alloys on W(110) substrate: Ab initio study Brice Rodrigue Malonda Boungou Structural, electronic and magnetic properties for Fe x Ni 1-x monolayer alloys on W(110) have been investigated, by considering the different size effect, using Density Functional Theory (DFT) calculations within the pseudopotential plane wave basis set method, including generalized gradient approximation (GGA) as the exchange-correlation potential . An antiferromagnetic coupling is found between Fe and Ni (W) atoms, when x coverage varying from 0.17 to 0.67, while for x ranging from 0.67 to 0.83 a ferromagnetic (antiferromagnetic) coupling is obtained between Fe and Ni (W). Consequently, the phase transition between the FM and AF occurs at x = 0.67 coverage. The interactions of the deposited monolayer alloy with the W substrate have led to a significant depreciation of the magnetic moments of Ni atoms, for all concentrations. A surface ripple is also shown with an inward (outward) relaxation for Ni (Fe) positions from the W subsurface layer. |
Monday, March 20, 2023 6:34AM - 6:47AM |
AA10.00007: Density-functional study of the thermodynamic properties and the pressure-temperature phase diagram of Mg2SiO Omamuyovwi Rita Jolayemi First-principles ab initio calculations were used to explore the structural and vibrational behavior of Mg 2 SiO 4 under compression. We show that at 10GPa and 12.2GPa, Mg 2 SiO 4 experiences a pressure-induced phase shift from Pnma to Imma and Imma to F3dm structure, respectively. From DFPT computation, we found that the forsterite structure (space group Pnma) is thermodynamically unstable due to frequencies less than zero. As a result, we used the free energy-based renormalisation approach, which allows DFT to calculate vibrational free energy even for materials having negative curvature of the potential energy surface in relation to atomic displacement. Furthermore, Kieffer's model depicted the vibrational density of states and thermodynamic features of pure substances in pressure-temperature space. |
Monday, March 20, 2023 6:47AM - 7:00AM |
AA10.00008: Electronic structure of strain-tunable Janus WSSe–ZnO heterostructures from first-principles Georgies A Asres Van der Waals (vdW) heterostructures, which are stacks of different types of 2D materials, offer the possibility to further tune and optimize the electronic properties of 2D materials. The electronic structure of semiconducting 2D materials, such as monolayer transition metal dichalcogenides (TMDs), are known to be tunable via environment and external fields. In this study, we calculate the structure and electronic characteristics of a vdW heterostructure of Janus monolayer WSSe and monolayer ZnO, both of which have out of plane dipole moments. Calculations are made and analysis is done to determine how this heterostructure's band edge energies and dipole moments are affected by alignment, biaxial and uniaxial strain, orientation, and electric field. We discover that the out-of-plane dipole moment of the ZnO monolayer is extremely sensitive to strain, resulting in the broad tunability of the heterostructure band edge energies over a range of experimentally relevant strains. The use of strain-tunable 2D materials to control band offsets and alignment is a general strategy applicable to other vdW heterostructures, one that may be advantageous in the context of clean energy applications, including photocatalytic applications, and beyond. |
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