Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session X37: Complex Oxides: Theory and ComputationFocus Live

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Sponsoring Units: GMAG DMP DCOMP Chair: Antia Botana, Arizona State University 
Friday, March 19, 2021 8:00AM  8:12AM Live 
X37.00001: Systematic Study of the Hubbard Model in Finite Magnetic Field via Determinant Quantum Monte Carlo Jixun Ding, Wen Wang, Yoni Schattner, Brian John Moritz, Edwin Huang, Thomas Devereaux Using determinant quantum Monte Carlo, we study the singleband Hubbard model in two dimensions, with electrons coupled to a constant outofplane magnetic field. We present thermodynamic, magnetic and transport properties of this model, including the local moment, compressibility, density of states, magnetoresistance, and hall conductivity, as a function of doping, temperature and Hubbard interaction strength. Our results are compared with experimental data, noninteracting and atomic limits, and other results obtained through alternative theoretical techniques. 
Friday, March 19, 2021 8:12AM  8:48AM Live 
X37.00002: Spinorbital entangled states in correlated molybdenum oxides Invited Speaker: George Jackeli We theoretically explore how the spinorbit coupling could give rise to unusual states of spinorbital or spinlattice degrees of freedom depending on the local delectron counting and the lattice geometry. We discuss d^{1} and d^{2} transition metal compounds, such as molybdenum oxides with double perovskite and pyrochlore structures, as candidate materials and consider available experimental rezults from this perspective. 
Friday, March 19, 2021 8:48AM  9:00AM Live 
X37.00003: Ferromagnetic kinetic exchange interaction in magnetic insulators Naoya Iwahara, Zhishuo Huang, Dan Liu, Akseli Mansikkamäki, Veacheslav Vieru, Liviu Chibotaru The superexchange theory predicts dominant antiferromagnetic kinetic interaction when the orbitals accommodating magnetic electrons are covalently bonded through diamagnetic bridging atoms or groups. In this work [1], we show that explicit consideration of magnetic and (leading) bridging orbitals, together with the electron transfer between the former, reveals a strong ferromagnetic kinetic exchange contribution. Firstprinciples calculations show that it is comparable in strength with antiferromagnetic superexchange in a number of magnetic materials with diamagnetic metal bridges such as FeCoFe complex and quasi 1D Cu chain compound (La_{4}Ba_{2}Cu_{2}O_{10}). In particular, it is responsible for a very large ferromagnetic coupling (−10 meV) between the iron ions in a Fe^{3+}−Co^{3+}−Fe^{3+} complex. Furthermore, we find that the ferromagnetic exchange interaction turns into antiferromagnetic by substituting the diamagnetic bridge with magnetic one. The phenomenology is observed in two series of materials, supporting the significance of the ferromagnetic kinetic exchange mechanism. 
Friday, March 19, 2021 9:00AM  9:12AM Live 
X37.00004: Ab initio prediction of quadruple perovskites with halfmetallic ferrimagnetism and high Curie temperatures duo wang, Monirul Shaikh, Saurabh Ghosh, Biplab Sanyal CaCu_{3}Fe_{2}Re_{2}O_{12}, a quadruple perovskite (QP) with the chemical formula AA’_{3}B_{2}B’_{2}O_{12}, shows halfmetallic ferrimagnetism with large magnetization and a high Curie temperature (T_{C}). Here we investigated a series of QPs using density functional theory and Monte Carlo simulations. We found that all compounds are ferrimagnetic with substituted A^{2+} (A=Ca, Sr, Ba, Pb) ions exhibiting high Tc (above 405 K), and the A^{3+} (A=Sc, Y, La ) substituted ones yielding even higher T_{C} (above 502 K). By examining interatomic exchange parameters, we found that the antiferromagnetic exchange couplings between Re and Cu as well as Re and Fe are responsible for this very high Curie temperature. For the compounds with A^{3+} substitution, electron doping in bands around the Fermi level dominated by the Re ions strengthen the ReCu and ReFe exchange interactions, which cause an increase in the T_{C}. This work demonstrates a design strategy of enhancing the spin ordering temperature by replacing Asite nonmagnetic ions. 
Friday, March 19, 2021 9:12AM  9:24AM Live 
X37.00005: Ab initio prediction of noncollinear, uniform magnetic structures MarieTherese Huebsch, Takuya Nomoto, MichiTo Suzuki, Ryotaro Arita The grand challenge in firstprinciples calculation for magnetic materials is whether we can predict the experimental magnetic structure for a given material. In particular, for noncollinear magnets there is a tremendous amount of possible magnetic configurations that ought to be considered. It is also known that ab initio calculations in the framework of spindensity functional theory (SDFT ) have many local minima. We present an efficient scheme [1] to circumvent these issues by a combination of the cluster multipole (CMP) theory to create an appropriate list of candidate magnetic configurations and SDFT. CMP+SDFT was proven to be reliable in predicting uniform magnetic structures in a highthroughput calculation including 2935 calculations and the effects of strong correlations on the prediction of magnetic structures is investigated by additional 1545 SDFT+U calculations. 
Friday, March 19, 2021 9:24AM  9:36AM Live 
X37.00006: Symmetry breaking in density functional theory captures bulk peculiarities that were assumed to exclusively emerge from electron correlation Zhi Wang, Oleksandr I. Malyi, Xingang Zhao, Alex Zunger Meanfield band theory, e.g., density functional theory (DFT), is often based on the symmetryrestricted, minimalcell model, with the smallest number of possible magnetic and structural degrees of freedom. Such symmetryrestricted DFT fails to reproduce many experimental observations, such as local distortions, mass enhancement, and nematicity (in some Febased materials). It has been argued that the strong correlation approach is the exclusive theory needed for describing such peculiarities. We report that by removing the constraint of the minimal cell, the energy minimization in DFT finds in enlarged cells (large enough to allow for symmetry breakings) atomic and spin symmetry breakings, which can explain many observed anomalies and provide close agreements with experiments. We show how the energylowering symmetry breaking effects in meanfield DFT capture mass enhancement [1] in a range of perovskites e.g. delectron SrVO3, SrTiO3, BaTiO3, LaMnO3 as well as pelectron CsPbI3 and SrBiO3, and local distortions and nematicity in ironbased compound FeSe [2]. Thus, symmetry breaking in DFT could describe effects that were previously attributed exclusively to complex correlated treatments. 
Friday, March 19, 2021 9:36AM  9:48AM Live 
X37.00007: Electronic structure and magnetic properties of hexaferrites: An ab initio study Churna Bhandari, Durga Paudyal Hexaferrites have been of huge research interest because of their technological applications in permanent magnets, data storage in computer hard disks and tapes, microwave devices, and wireless communications. Finding suitable hexaferrite that can exhibit a strong uniaxial magnetocrystalline anisotropy energy (MAE) and high coercivity is still an open question today for improvement of the device efficiency. We study the electronic structure, magnetic properties, and magnetostructural transition in Sr/La hexaferrites using advanced density functional methods. Our calculations suggest that Lasubstituted compounds enhance the MAE while transforming from P6$_3$/mmc structure (high temperature phase) to P$\bar{6}m$_2$ structure (low temperature phase) compared to {\it sp}electron based hexaferrites. The underlying physics in the enhancement of MAE relies in the electronic changes resulting from local crystalline environment of Featoms nearest to the La. Using an anisotropic energy density model, we show that the contribution of higher order anisotropy constants plays significant role in describing the experimentally measured MAE. 
Friday, March 19, 2021 9:48AM  10:00AM Live 
X37.00008: False metals and real insulators Oleksandr Malyi, Alex Zunger Very often, the prediction of metallic electronic structure in meanfield theory for compounds known to be insulators (listed below) is attributed to a lack of correlation. We show that the intricate coupling of electronic, spin and lattice degrees of freedom afforded by symmetry broken meanfield theories such as DFT (rather than strong or dynamic correlation) correctly predicts the appropriate insulating or metallic state in a range of compounds. The symmetrybreaking modes that lower the total energy while opening a gap include: 
Friday, March 19, 2021 10:00AM  10:12AM Live 
X37.00009: Phononinduced antiferromagnetism in two dimensions Xun Cai, Zixiang Li, Hong Yao Antiferromagnetism (AF) such as Neel ordering is often closely related to strong local Coulomb repulsion such as onsite Hubbard repulsion in twodimensional (2D) systems. Whether Neel AF ordering in 2D can be dominantly induced by electronphonon couplings has not been completely understood. Here, by employing numericallyexact signproblemfree quantum Monte Carlo (QMC) simulations, we obtain convincing evidences that SuSchriefferHeeger (SSH) phonons can induce Neel AF ordering on the square lattice for a wide range of phonon frequencies. In the limit of vanishing phonon frequency (namely in the adiabatic limit), the SSH phonons favor a valencebond solid (VBS) ordering. By increasing the phonon frequency, we show that there is a direct (and possibly deconfined) quantum phase transition from the VBS to AF phases. 
Friday, March 19, 2021 10:12AM  10:24AM Live 
X37.00010: Computational design of layeredoxide materials Shree Ram Acharya, Timothy E Ferreira, Athena S. Sefat, Valentino Cooper Layeredoxides have been known to host high temperature superconductivity since the discovery of cuprates. The coupling between structure and magnetism has been suggested as important factor for defining the functional properties of these materials. Despite the potential impacts, there are only a few synthesized layered oxides. Recent success in the synthesis of layered structures from threedimensional perovskites have aimed to fill this knowledge gap by providing novel routes to synthesizing materials with desired properties. We present the feasibility of creating layered ABO_{2} structures from ABO_{3} (A=Ca, La, Sr, Li, Na, Nd, Pr, Y; B=Fe, Mn, Mo, V, Ni, Ru) perovskites. The oxygen vacancy formation energetics from highthroughput firstprinciples calculations are used as descriptors for phase transformation. The stability against decomposition into binary oxides and thermodynamic analyses of the formation conditions in terms of chemical potential of the components are presented to guide the experimental synthesis. The magnetic ground state of the ABO_{2 }structures, the exchange interaction parameters, and the Neel temperature from Monte Carlo simulations are explored as potential indicators of superconductivity. 
Friday, March 19, 2021 10:24AM  10:36AM Live 
X37.00011: Nonlinear spin and orbital susceptibilities of a Mott insulator Zachariah Addison, Sayantan Roy, Nandini Trivedi We investigate the coupling of electromagnetic fields to electrons on a lattice with strong onsite Hubbard interactions and calculate the spin and orbital nonlinear electric field susceptibilities. Gauge covariance of the equations of motion for both the photon and matter fields prescribes a minimal coupling procedure in which the fermionic quantum momentum operator is boosted by the electromagnetic vector potential. On a lattice this minimal coupling procedure takes the form of a Peierls substitution whereby the electronic wavefunction acquires a phase upon transport through the electromagnetic field. Strong electronelectron interactions can localize the charge degrees of freedom on a lattice forcing the Peierls phase to vanish. We show how the relativistic corrections in Dirac equation give rise to effective spinspin interactions that couple directly to an external electric field even in the absence of a Peierls phase. 
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