Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session U50: Metal Insulator Transition Theory |
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Sponsoring Units: DCMP Chair: Yan Wang, Oak Ridge National Laboratory Room: Mile High Ballroom 1C |
Thursday, March 5, 2020 2:30PM - 2:42PM |
U50.00001: Avalanche induced co-existing localised and thermal regions in disordered spin chains Philip Crowley, Anushya Chandran We investigate the stability of an Anderson localised chain to the inclusion of a single finite interacting thermal seed. This system models the effects of rare low-disorder regions on many-body localised chains. Above a threshold value of the mean localisation length, the seed causes runaway thermalisation in which a finite fraction of the orbitals are absorbed into a thermal bubble. This `partially avalanched' regime provides a simple example of a delocalised, non-ergodic dynamical phase. We derive the hierarchy of length scales necessary for typical samples to exhibit the avalanche stability, and show that the required seed size diverges at the avalanche threshold. We introduce a new dimensionless statistic that measures the effective size of the thermal bubble, and use it to numerically confirm the predictions of avalanche theory in the Anderson chain at infinite temperature. |
Thursday, March 5, 2020 2:42PM - 2:54PM |
U50.00002: Oxygen vacancy effect on the electronic structure of LaNiO3 using first-principles Xingyu Liao, Hyowon Park, Vijay Singh While bulk LaNiO3 remains metallic at all temperatures, many experiments show that LaNiO3-x exhibits the metal-insulator transition as the oxygen vacancy level x goes from 0 to 0.5. In addition to the resistivity data, both photoelectron and X-ray absorption spectroscopy works show some intriguing features that cannot be explained based on density functional theory (DFT). In this talk, I will present DFT plus dynamical mean field theory (DMFT) calculations of LaNiO3-x for x=0, 0.25, and 0.5 in different magnetic states. Our DFT+DMFT method was implemented using the maximally localized Wannier function as local orbitals for the correlated subspace. While the DFT density of states (DOS) is similar to experimental spectroscopy data for LaNiO3, it failed to describe the insulating ground state and the peak splitting of unoccupied DOS as x increases to 0.5. Our DFT+DMFT calculations can capture both the resistivity change as well as the spectral features arising from the oxygen vacancy. We find that both the crystal splitting and the Ni d valence changes due to the oxygen vacancy play important roles in explaining the electronic structure. We will also discuss both similarity and difference of vacancy effects between the bulk and ultra-thin film structures. |
Thursday, March 5, 2020 2:54PM - 3:06PM |
U50.00003: The metal-to-insulator transition in polar metals Evan Sheridan, Cedric Weber, Sinéad Griffin, Jeffrey Neaton The fundamental design principles that drive a switchable polarity in oxide-based |
Thursday, March 5, 2020 3:06PM - 3:18PM |
U50.00004: Phase transition and instability in dimensionality-controlled artificial oxide crystals Taewon Min, Seunggyo Jeong, Woo Seok Choi, Jaekwang Lee The metal-insulator transition (MIT) is one of the fascinating physical phenomena in complex oxide system, and that has inspired the physics community during the last 20th century. In particular, recent advances in atomically controlled growth of oxide material have enabled the realization of artificial crystals with customized dimensions. Herein, by combining density functional theory calculations with optical and electrical measurements, we investigate dimensionality-induced MIT in atomically well-defined SrRuO3/SrTiO3 (SRO/STO) superlattices. We note that SRO/STO superlattices favor an antiferromagnetic insulating state as the SRO layers are getting thinner, which indicates that MIT is strongly coupled with magnetic ordering. Furthermore, we find that electronic and magnetic instabilities in the two SRO unit cell induce thermally-driven MIT along with magnetic transition. Novel theoretical finding will be presented along with transport and optical observations. |
Thursday, March 5, 2020 3:18PM - 3:30PM |
U50.00005: Theory of Dipole Insulators Oleg Dubinkin, Julian May-Mann, Taylor L Hughes Insulating systems are characterized by their insensitivity to twisted boundary conditions as quantified by the charge stiffness and charge localization length. The latter quantity serves as a universal criterion to distinguish between metals and insulators. In this work we extend these concepts to a new class of quantum systems having conserved charge and dipole moments. We refine the concept of a charge insulator by introducing notions of multipolar insulators, e.g., a charge insulator could be a dipole insulator or dipole metal. We develop a universal criterion to distinguish between these phases by extending the concept of charge stiffness and localization to analogous versions for multipole moments, but with our focus on dipoles. This refined structure allows for the identification of phase transitions where charge remains localized but, e.g., dipoles delocalize. We illustrate the proposed criterion using several exactly solvable models that exemplify these concepts. |
Thursday, March 5, 2020 3:30PM - 3:42PM |
U50.00006: Disorder in the one-dimensional half-filled extended Hubbard model Jon Spalding, Ka-Ming Tam, David K Campbell, Shan-Wen Tsai The addition of disorder to interacting electron systems presents a challenging theoretical problem. In this talk, I will describe the effects of disorder on the phase diagram of the extended Hubbard model in one spatial dimension. Our theoretical analysis is possible in the weak coupling and weak disorder case due to the low dimensionality. |
Thursday, March 5, 2020 3:42PM - 3:54PM |
U50.00007: Electronic and Lattice Dynamical Properties of MgTa2O6 Kyle Miller, James Rondinelli Materials exhibiting metal-insulator transitions (MIT) are proposed platforms for next-generation low-power electronics. In addition, most of these materials exhibit strong coupling between the electronic and lattice degrees-of-freedom, which makes them ideal systems to examine the interplay between lattice dynamics, electronic structure, and magnetic order. Well-studied rutile-structured MIT oxides, such as VO2 and NbO2, exhibit dimerized cations within the edge-connected octahedra along the c axis in the insulating state. Analogous compounds with the related trirutile superstructure, e.g., V2WO6 and CuSb2O6, exhibit a similar dimerization. Here we investigate the propensity for MIT in MgTa2O6, a d0 insulator, upon electron doping. Our calculations suggest that MgTa2O6 remains metallic for electron doping configurations within the d0.25-d0.5 range, whereas Ta-Ta dimerization occurs for higher electron concentations. Overall, these results indicate that trirutile oxides may be a promising materials class for which to functionalize MITs. |
Thursday, March 5, 2020 3:54PM - 4:06PM |
U50.00008: Theoretical study of electronic and structural phase transitions in MPS3 with M = (Fe, Ni, Mn, Co) Minsung Kim, Heung-Sik Kim, Kristjan Haule, David Vanderbilt Metal phosphorus trisulfides (MPS3 with M = Fe, Ni, Mn, Co) are layered materials which show Mott-insulator-to-metal transitions under the application of pressure. In addition, some of the compounds are reported to undergo structural phase transitions, making the theoretical description of the phase transitions more complicated. Here, we investigate the electronic and structural phase transitions of representative MPS3 compounds using first-principles methods based on density functional theory and dynamical mean-field theory. We discuss the origin and the relation of the two types of phase transitions and clarify the role of the electron correlation and interlayer stacking configurations. We also examine how different metal species change the evolution of the phases under pressure. Our results provide needed theoretical understanding of these tunable Mott insulators. |
Thursday, March 5, 2020 4:06PM - 4:18PM |
U50.00009: Insight into the insulator-to-metal transition in ruthenium A2Ru2O7 pyrochlores Danilo Puggioni, Geneva Laurita, Ram Seshadri, James Rondinelli The study of insulator-to-metal transitions (IMT) is of interest from the viewpoint of fundamental understanding of the underlying physics, and that materials at such a brink often can be harnessed for useful functionality. Here, using first principle calculations, we study the role of disorder, in the form of cation off-centering, on the compositionally-controlled IMT in the oxide pyrochlore (Pr1−xBix)2Ru2O7. Our results suggest the combination of primary and secondary (due to size) electronic effects of the lone pair-driven incoherent cation displacements are responsible for the metallic state of pyrochlores with Bi substitution. |
Thursday, March 5, 2020 4:18PM - 4:30PM |
U50.00010: Metal-insulator transition in a Hubbard model with random and all-to-all hopping and exchange Grigory Tarnopolsky, Subir Sachdev We examine a N site Hubbard model with an on-site repulsion U, and random and all-to-all hopping, t, and exchange J. In the large N limit, the problem reduces to a single site symmetric Anderson impurity coupled to self-consistent bosonic and fermionic baths. We present large M (for a model with SU(M) spin symmetry) and renormalization group analyses of a metal-insulator transition in this model. |
Thursday, March 5, 2020 4:30PM - 4:42PM |
U50.00011: Many Body Localization Due to Correlated Disorder in Fock Space Soumi Ghosh, Atithi Acharya, Subhayan Sahu, Subroto Mukerjee The Hamiltonian of an interacting system of spinless fermions looks like that of a single particle hopping on a Fock graph in the presence of a random disordered potential. The coordination number of the Fock graph increases linearly with the system size L in 1D. Thus, in the thermodynamic limit, the disordered interacting problem in 1D maps on to an Anderson model with infinite coordination number. Despite this, this system displays localization which appears counterintuitive. The resolution lies in the on-site disorder on the Fock graph being highly corelated as they are derived from an exponentially smaller number of on-site disorder potentials in real space. Thus, such correlations have a strong effect on the localization properties of the corresponding many-body system. In this work we perform a systematic quantitative exploration of the nature of correlations of the Fock space potential required for localization. We show that changing the correlation strength can induce thermalization or localization in systems. We find that a linear variation of correlations with Hamming distance in Fock space is drives a thermal-MBL phase transition where the transition is driven by the correlation strength. Systems with the other forms of correlations we study are found to be ergodic. |
Thursday, March 5, 2020 4:42PM - 4:54PM |
U50.00012: Current driven first order metal-metal martensitic phase transitions in correlated electron systems Stewart Barnes As a function of temperature and pressure, a number elemental 3d metals such as Fe or V undego first order martensitic phase transitions between bcc and fcc structures. Similar metal to metal first order phase transitions occur in other transition metals and alloys including most famously shape memory alloys. In analogy with the spin Berry phase, defined is an electro-mechamical such phase defined by the four connection Aμ that couples to the conduction electron charge current. It is implied that, for highly pure wires of such materials, an electronic charge current can drive say the bcc to fcc martensitic phase transition of a suitable metrial well below the strain, temperature and/or pressure that which this usually occurs. This leaves the material in a higher energy state thereby converting electrical to lattice energy in much the same manner as currents can drive a magnetic state to higher energy. The theory also applies to domain walls in conducting ferro and antiferroelectric meterials. |
Thursday, March 5, 2020 4:54PM - 5:06PM |
U50.00013: Theoretical phase diagram of unconventional alkali-doped fullerides Theja De Silva By constructing an effective model based on recently calculated ab initio bare interaction parameters, we study the phase diagram of alkali-doped fullerides as a function of temperature and internal pressure. While we use a slave-rotor mean-field theory to determine the metal-insulator-superconductor phase boundaries, we use a variational mean-field approach to detect the magnetic phase transitions. We find a good agreement with experimental phase diagram in both weak and strong coupling limits. We explain the unified description of the phase diagram including the proximity of s-wave superconducting state and the Mott-insulating state, and the existence of Jahn-Teller distorted metallic state using orbital selective physics. We argue that the double electronic occupation of two degenerate orbitals triggers both s-wave superconductivity and Jahn-Teller distortion. While the orbital ordering of two electrons causes the distortion, the remaining single electron in the third orbital causes the metal-insulator transition. |
Thursday, March 5, 2020 5:06PM - 5:18PM |
U50.00014: Operator growth in disordered systems, a translation invariant approach Xiangyu Cao Operator growth in disordered systems, a translation invariant approach |
Thursday, March 5, 2020 5:18PM - 5:30PM |
U50.00015: Electrostatic gating Effects on the Metal to Mott Insulator Transition of NiS2: a DFT+DMFT study Ezra Day-Roberts, Turan Birol, Rafael Fernandes Electrostatic gating provides a convenient way to manipulate carrier densities without introducing defects that lead to impurity scattering as in chemical doping. Recent advances, including those in ionic liquid and gel gating, have allowed experimental access to a much larger range of added carrier concentrations. NiS2, in the pyrite structure, is a Mott insulator that has previously been found to undergo a metal-to-insulator transition (MIT) as function of isovalent selenium substitution as well as pressure. This suggests that NiS2 is near the edge of the MIT, making it a good candidate material to be electrostatically driven across the MIT. Here, we present results of a first-principles study of this material using fully charge self-consistent Dynamical Mean Field Theory (DFT+DMFT). We explore the properties of NiS2 across the MIT as a function of temperature and added carrier concentration, contrasting the cases of electrostatic gating and chemical doping. |
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