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 Q28: Computational Design, Understanding and Discovery of Novel Materials VIFocus
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Sponsoring Units: DMP Chair: Jorge Munoz, University of Texas at El Paso Room: Room 220 |
Wednesday, March 8, 2023 3:00PM - 3:36PM |
Q28.00001: Intercalated moiré systems as a new class of quantum materials and using computation to accelerate phase space searches Invited Speaker: Sinead M Griffin Since the discovery of superconductivity in twisted bilayer graphene, moiré materials have been found to host many emergent quantum phenomena ranging from fractionalized excitations with non-trivial topology to Wigner crystal states. Recent work has augmented the huge parameters space in moiré materials of stacking, gating and twisting by the addition of intercalated atomic and molecular species between homo- and heterobilayers of 2D materials. In this talk, I will discuss our recent work on predicting novel emergent phenomena in intercalated 2D moiré systems using first-principles, symmetry analysis, and phenomenological approaches. This includes the prediction of a new route to achieving hard 2D magnets and topological superconductivity in collaboration with experimental groups. I will also discuss the prospects for the fine tuning of crystal-field environments of the intercalated species via moiré engineering. I finally highlight the enormous design space of find correlated emergent phenomena as a new class for designer quantum materials and the role of computational studies in rapidly identifying promising regions of phase space. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q28.00002: A computational framework accompanied by machine learning techniques for designing two-dimensional/organic hybrid quantum materials Srihari M Kastuar, Christopher Rzepa, Chinedu E Ekuma, Srinivas Rangarajan Due to their exotic and tunable optoelectronic properties, two-dimensional (2D)/organic hybrid materials formed by intercalating conjugated organic molecules within the van der Waals gap of 2D-based transition metal chalcogenides are promising quantum materials. Nonetheless, developing and screening a database of millions of such potential materials remains a difficult task. We have created a computational framework that allows us to design molecular intercalated 2D material families, model such hybrid materials in a high-throughput manner, and analyze their properties using first-principles methods. We have also developed a machine learning algorithm that exploits and analyzes the designed hybrid material database based on several metrics such as the intercalation energy in order to identify promising quantum materials for further computational and experimental investigation. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q28.00003: Ab Initio Investigations of Kagome Xenes Chenhaoyue Wang, Amartya S Banerjee Materials with dispersionless electronic states (or flat bands) have been intensely investigated in recent years, owing to their association with strongly correlated electrons. Due to the negligible kinetic energies of electrons in such states, the electron-electron interaction dominates, thus resulting in superconductivity, ferromagnetism, and other exotic phases of matter, as exemplified famously by twisted bilayer graphene. However, the discovery of new low-dimensional flat band materials, especially elemental ones, remains a challenge. First principles calculations based on Density functional theory (DFT) have shown recently that the 2-dimensional carbon kagome lattice is structurally stable and has a flat band around its Fermi level. Here, in order to seek novel stable elemental 2D materials with flat bands, we utilize DFT to systematically study other Group IVA elements, in Kagome lattice configurations. We show that these Kagome Xenes (X = C, Si, Ge, Sn, Pb) all generically support flat bands, but unlike their carbon counterpart, they do not prefer planar structures. We discuss various electro-mechanical properties of these materials and provide contrasts with the corresponding classical hexagonal-lattice Xenes (i.e., silicene, germanene, stanine and plumbene). |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q28.00004: Stability of layered Li-Mg-B compounds from first-principles Charlsey Tomassetti, Gyanu P Kafle, Igor I Mazin, Aleksey Kolmogorov, Elena R Margine Numerous metal borides with honeycomb boron networks have been considered in the past two decades in the search for MgB2-type superconductors. One of the most promising candidates, a layered LiB compound with desired structural and electronic features, has been recently synthesized in diamond anvil cells and predicted to have a critical temperature above 32 K under ambient pressure. Based on our present re-examination of the LiB thermodynamic stability at different (T,P) conditions, we propose that the desired phase could be obtained at lower pressures starting with a delithiated LiBy compound. We also assess the feasibility of making related Li-Mg-B materials and demonstrate that layered compounds with targeted layered morphologies are metastable under typical synthesis conditions. |
Wednesday, March 8, 2023 4:12PM - 4:24PM Author not Attending |
Q28.00005: Triangular ad-atom surface lattices as a platform for correlated Hund's physics Henri Menke, Michel Bockstedge, Philipp Hansmann In the triangular lattice Hubbard model, the interplay of strong correlations and geometrical frustration gives rise to a variety of emergent phenomena. At intermediate coupling a metal-insulator transition is observed and spin liquid physics have been proposed, whereas at strong coupling a magnetic insulator is found. Triangular lattice structures can be realized in a variety of materials, such as layered transition metal dichalcogenides, organic salts of the ?-ET family, or X:Si(111) ad-atom systems (X = Pb, Sn, C), where various kinds of correlated phenomena have been observed. In this work we propose X:SiC(0001) ad-atom systems (X = Cr, V, Ti) as a new platform to control and probe two-band physics in the triangular lattice Hubbard model. In particular we expect Hund's coupling to play a major role in the physics of V:SiC(0001). We use first-principles density functional theory calculations in conjunction with the constrained random phase approximation to derive a material-realistic model for the electronic structure. Using dynamical mean-field theory we explore the phase diagram as a function of ad-atom species and temperature. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q28.00006: Understanding Disorder-driven Metal-Insulator Transitions in Heteroanionic TiOF Siddhartha Nathan, James M Rondinelli Temperature-driven metal insulator transitions (MITs), occurring when the metallic state transforms into an insulating state at lower temperatures, or vice versa, hold great potential for applications in next-generation electronic devices. The underlying interactions governing the MITs in oxides arise from a combination of factors: electronic correlations, metal-metal bonding and lattice distortions (dimerization) cooperatively interact to drive the transition. Here, we investigate the behavior of the rutile-structured heteroanionic oxyfluoride TiOF using first principles simulations as a route to disentangle various contributions to MITs in the d1 rutile family. We first model the structure of TiOF using edge-sharing fac ordered [TiO3F3] heteroleptic units and explore the effects of magnetism and electron correlation. We also construct a cluster expansion model to understand the interactions that govern the short- and long-range anion order in TiOF and its consequence on the observed insulating and paramagnetic behavior, demonstrating the robustness of our method in disentangling the dependencies of electronic and magnetic properties on these parameters. Ultimately, our work provides improved understanding on anion ordering tendencies in heteroanionic MIT materials and offers insights on synthetically achieving anion order on length scales necessary for device applications. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q28.00007: Anharmonic and kinetic effects on the stabilization pressure of high-Tc clathrate hydrides Roman Lucrezi, Christoph Heil, Lilia Boeri, Simone di Cataldo We recently reported the theoretical prediction of novel high-performing clathrate hydride superconductors, such as LaBH8, SrSiH8, and BaSiH8. Within harmonic phonon calculations, we determined the minimum pressures of dynamical stability in these clathrates to be below 40 GPa, while retaining the superconducting state up to temperatures in the order of 100 K. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q28.00008: Ab initio analysis of Li-B-C structure stability Saba Kharabadze, Maxwell Meyers, Charlsey Tomassetti, Elena R Margine, Igor I Mazin, Aleksey Kolmogorov Prediction of high-Tc superconductivity in hole-doped LixBC two decades ago has brought about an extensive effort to synthesize new materials with honeycomb B-C layers but the thermodynamic stability of Li-B-C compounds remains largely unexplored. In this study, we use density functional theory to characterize well-established and recently reported Li-B-C phases. Our calculation of the Li chemical potential in LixBC helps estimate the (T,P) conditions required for delithiation of the LiBC parent material, while examination of B-C phases helps rationalize the observation of metastable BC3 polymorphs. At the same time, some of the previously reported crystal structure phases appear to be thermodynamically and kinetically inaccessible. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q28.00009: Imaginary phonon modes and phonon-mediated superconductivity in Y2C3 Niraj Nepal, Paul C Canfield, Lin-Lin Wang In high-throughput computation to search for new phonon-mediated superconductors, compounds with calculated imaginary frequency phonon modes are regarded as dynamically unstable and often discarded as promising candidates. Using density functional perturbation theory (DFPT) to investigate Y2C3 with an experimentally measured Tc ~ 18 K, we find imaginary optical phonon modes in its high symmetric body-centered cubic (BCC) structure. By following the imaginary phonon modes to distort the structure, we find the low-symmetry structures have lower electronic total energy than the BCC structure. Our electron-phonon coupling (EPC) calculations then reveal that the strong EPC contributions from these low-energy optical phonon modes are responsible for the observed sizable Tc. Our work shows that compounds with the calculated dynamical instability should not be simply excluded in the high-throughput search for new phonon-mediated superconductors. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q28.00010: New carbon allotropes and their B-doped phases as candidate for Q-carbon materials with magnetic and superconducting properties Reo Kita, Masayuki Toyoda, Susumu Saito Recent experimental studies have indicated that quenched sp2-sp3 hybridized carbon materials (Q-carbon) exhibit ferromagnetism with relatively high Curie temperature [1] and even superconductivity with high critical temperature (Tc) in their B-doped phases [2]. However, local structure of Q-carbon has not been clarified yet. Therefore, further theoretical studies are indispensable. Here we propose a new carbon allotrope with similar concentration of sp2-sp3 hybridized atoms to Q-carbon. We study their electronic properties including related allotropes previously proposed so far based on the density functional theory (DFT). Only the carbon allotrope we newly propose is found to exhibit magnetic moment which is closer to experimental value [1]. We further estimate Tc of the B-doped allotropes using the McMillan formula and the density functional perturbation theory (DFPT). The estimated Tc value for carbon allotrope with an appropriate B concentration also agrees well with the experimental value [2], indicating that our new allotrope and its B-doped phases are good candidate for Q-carbon. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q28.00011: First-principles prediction of structural, magnetic properties of Cr-substituted strontium hexaferrite, and its site preference Binod Regmi To investigate the structural and magnetic properties of Cr-doped M-type Strontium hexaferrite (SrFe12O19) with x = (0.0, 0.5, 1.0), we perform first-principles total-energy calculations based on density functional theory. Based on the calculation of the substitution energy of Cr in Strontium hexaferrite and formation probability analysis, we conclude that the doped Cr atoms prefer to occupy the 2a, 12k, and 4f2 sites which is in good agreement with the experimental findings. Because Cr3+ ion’s atomic magnetic moment, 3µB, is smaller than that of Fe3+ion, 5µB, saturation magnetization Ms reduces rapidly as the concentration of Cr increases in strontium hexaferrite. The magnetic anisotropic field (Ha) rises with an increasing fraction of Cr despite a significant reduction of magnetization and a slight increase of magnetocrystalline anisotropy (K1). The cause for the rise in magnetic anisotropy field (Ha) with an increasing fraction of Cr is further emphasized by our formation probability study. Cr3+ ions prefer to occupy the 2a site at lower temperatures, but as the temperature rises, it is more likely that they will occupy the 12k site due to its higher multiplicity. Cr3+ ions are more likely to occupy the 12k site than the 2a site at a specific annealing temperature (>700°C). |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q28.00012: First-principles calculations to investigate stability and electronic properties of ferromagnetic (anti-ferromagnetic) semiconducting Heusler alloys Cr2YSi (Cr2YAl) Ridwan Nahar, Ka Ming Law, Sujan Budhathoki, Michael Zengel, Thomas Roden, Justin Lewis, Adam Hauser The phase structure and properties of Heusler alloys Cr2YZ (Z = Al, Si) have been studied using first principles calculations. The L21-type cubic structure found to be energetically preferred to the XA inverse Heusler phase, and with strong ferromagnetic (Cr2YSi) and anti-ferromagnetic (Cr2YAl) properties. Electronic structure and magnetic property calculations predict that Cr2YAl is a semiconducting antiferromagnet. On the other hand, L21-type Cr2YSi shows a high spin polarization and a direct band gap, suggesting promise as a spintronic semiconducting ferromagnet. The effect of tetragonal distortion and Hubbard U correction to exchange-correlation on the physical nature of these alloys are studied and will be discussed. Progress toward experimental realization in bulk or thin film form will also be presented. |
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