Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q46: Strongly Correlated Electron Systems: Hubbard Model and other Many Body Theories |
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Sponsoring Units: DCMP Chair: Hae-Young Kee, University of Toronto Room: Mile High Ballroom 4E |
Wednesday, March 5, 2014 2:30PM - 2:42PM |
Q46.00001: Accuracy of the downfolding scheme for multiorbital Hubbard models Hiroshi Shinaoka, Philipp Werner, Matthias Troyer Deriving an effective low-energy model from \textit{ab initio} calculations is a grand challenge in condensed matter physics. Recently, the so-called constrained random phase approximation (RPA) has been developed. In that scheme, screening effects by high-energy bands are taken into account in the RPA level to derive screened Coulomb interactions in the low-energy model. The method has been applied to various strongly correlated electronic systems such as transition metal oxides and organic compounds in combination with \textit{ab initio} band calculations. However, the accuracy of the scheme still needs to be clarified. In this talk, we discuss the accuracy of this scheme using a multi-orbital Hubbard model. We first derive a low-energy effective single-orbital Hubbard model using the constrained RPA scheme. We then solve both models using dynamical mean-field theory, compare the results and discuss the accuracy of the downfolding scheme. [Preview Abstract] |
Wednesday, March 5, 2014 2:42PM - 2:54PM |
Q46.00002: A variational cluster study of possible phase separation in square and honeycomb Hubbard lattices Kun Fang, Gayanath Fernando, Alexander Balatsky, Armen Kocharian The Hubbard model is examined for possible electronic phase separation using the variational cluster approximation in square and honeycomb geometries. The phase separation is found when different electronic states with different electronic densities $n$ share the same chemical potential $\mu$, so that these states can coexist at equilibrium and be distributed inhomogeneously throughout the lattice. The phase separation is clearly identified in the square lattice but, surprisingly, it is not discovered in the honeycomb lattice in a similar region of on-site Coulomb interaction and hole doping. The phase separation instability found in the square lattice is signatured by the disappearance of a set of one particle spectra around the $k$-point $(\pi/2,\pi/2)$ in momentum space. The electronic state associated with the set of spectra is due to scattering of electrons at the antiferromagnetic (AF) Brillouin zone boundaries and responsible for the phase separation. To our knowledge, no previous publications reveal such an anomalous state. The honeycomb lattice does not show the corresponding anomalies due to its different geometry, so that there is no such phase separation in the honeycomb lattice. Our VCA provides strong support for phase separation instability driven by electronic cor [Preview Abstract] |
Wednesday, March 5, 2014 2:54PM - 3:06PM |
Q46.00003: Finite-temperature superconducting correlations in the square lattice Hubbard model Ehsan Khatami, Richard Scalettar, Rajiv R.P. Singh We utilize numerical linked-cluster expansions (NLCE) [1,2] to study superconducting properties of the repulsive Fermi-Hubbard model on the square lattice. Within NLCE, temperature-dependent properties in the thermodynamic limit can be obtained from exact diagonalization of small clusters. We calculate the pairing correlation functions, structure factor, and correlation length for d-wave and extended s-wave symmetries at, and especially away from, half filling for a wide range of interaction strengths. A relatively strong tendency to d-wave pairing away from half filling is revealed after subtracting the uncorrelated contributions. We compare our findings to improved results from the determinantal quantum Monte Carlo simulations on large finite clusters with periodic boundary condition.\\[4pt] [1] M. Rigol, T. Bryant, and R. R. P. Singh, Phys. Rev. Lett. 97, 187202 (2006).\\[0pt] [2] E. Khatami and M. Rigol, Phys. Rev. A 84, 053611 (2011). [Preview Abstract] |
Wednesday, March 5, 2014 3:06PM - 3:18PM |
Q46.00004: Principle of Maximum Entanglement Entropy and Local Physics of Correlated many-body Electron-Systems Nicola Lanata, Hugo Strand, Yongxin Yao, Gabriel Kotliar We argue that, because of the quantum-entanglement, the local physics of the strongly-correlated materials at zero temperature is described in very good approximation by a simple generalized Gibbs distribution, which depends on a relatively small number local quantum thermodynamical potentials. We demonstrate that our statement is exact in certain limits, and we perform numerical calculations of the iron compounds FeSe and FeTe and of the elemental cerium by employing the Gutzwiller Approximation (GA) that strongly support our theory in general. [Preview Abstract] |
Wednesday, March 5, 2014 3:18PM - 3:30PM |
Q46.00005: Maximally Entangled Mode, Metal-Insulator Transition and Violation of Entanglement Area Law in Non-interacting Fermion Ground States Mohammad Pouranvari, Kun Yang We study in this work the ground state entanglement properties of two models of non-interacting fermions moving in one-dimension (1D), namely random dimer model and power-law random banded model that exhibit metal-insulator transitions. We find that entanglement entropy grows either logarithmically or in a power-law fashion with subsystem size in the metallic phase or at metal-insulating critical point, thus violating the (1D version of) entanglement area law. No such violation is found in the insulating phase. We further find that characteristics of \emph{single fermion} states at the Fermi energy (which can \emph{not} be obtained from the many-fermion Slater determinant) is captured by the lowest energy single fermion mode of the \emph{entanglement} Hamiltonian; this is particularly true at the metal-insulator transition point. In addition, the inverse-participation ratio of the lowest energy single fermion mode of the {\em entanglement} Hamiltonian is proportional to that of the single fermion state at Fermi energy in all cases. Our results suggest entanglement is a powerful way to detect metal-insulator transitions, \emph{without} knowledge of the Hamiltonian of the system. Results on metal-insulator transition of 3D Anderson model will also be presented. [Preview Abstract] |
Wednesday, March 5, 2014 3:30PM - 3:42PM |
Q46.00006: Minimally entangled typical thermal states of fermions in DMRG++ Gonzalo Alvarez I will discuss the minimally entangled typical thermal states (METTS) algorithm (developed by White in PRL 2009) in the context of fermionic systems such as the Hubbard model. The additional idea here (http://prb.aps.org/abstract/PRB/v87/i24/e245130) is to combine METTS with the Krylov-space approach to evolve the classical product states in imaginary time. The issues to be addressed include ergodicity, ``collapse'' bases, and convergence. For the temperature dependence of the superconducting correlations, METTS will be shown to yield the correct exponential decay with distance, and exponents proportional to the temperature at low temperatures. The talk will conclude with a few remarks about recent directions and future plans for DMRG++ (\verb!https://web.ornl.gov/~gz1/dmrgPlusPlus/!) and related codes. [Preview Abstract] |
Wednesday, March 5, 2014 3:42PM - 3:54PM |
Q46.00007: Dual boson approach to collective excitations in correlated fermion system Hartmut Hafermann, Erik G.C.P. van Loon, Alexey N. Rubtsov, Olivier Parcollet, Alexander I. Lichtenstein, Mikhail. I. Katsnelson We describe the interaction between electrons and collective excitations in strongly correlated fermion systems by means of the so-called dual boson approach. It includes nonlocal corrections to extended dynamical mean-field theory (EDMFT) and is applicable to lattice fermion models with both short- and long-range interaction. We present results for the collective charge excitations in the (extended) Hubbard model and show that through the inclusion of vertex corrections to the polarization operator, the approach correctly describes the long wavelength collective excitations in the strong coupling regime. In particular, we find the zero sound mode when forces are short-ranged and plasmons in presence of a long-range interaction. We further examine the effects of nonlocal correlations in the extended Hubbard model and compute the phase diagram. Results are compared to EDMFT and the random phase approximation. [Preview Abstract] |
Wednesday, March 5, 2014 3:54PM - 4:06PM |
Q46.00008: The Holstein polaron: beyond the standard model Carl J. Chandler, Frank Marsiglio The paradigm for describing the polaron is the Holstein model, where only local interactions between the electron and optical phonon modes are considered. We present several variants of this model and discuss the impact on various observables, such as the effective mass. Possible variations include further than nearest neighbour hopping, longer range interactions, and even models that go beyond the Holstein/Frohlich coupling, i.e. the BLF/SSH (Barisic-Labbe-Friedel/Su-Schrieffer-Heeger) model. Recent progress on these models will be described. [Preview Abstract] |
Wednesday, March 5, 2014 4:06PM - 4:18PM |
Q46.00009: On the separability of dynamical and non-local self-energy effects in correlated materials Jan M. Tomczak We employ Hedin's {\it GW} approximation to correlated metals such as the iron pnictide and chalcogenide superconductors, and the transition metal oxide SrVO$_3$. We find that non-local correlation effects in these systems are non-negligible, and indeed crucial for agreement with experimental observations. This advocates that the gold standard for strongly correlated materials, dynamical mean field theory (DMFT), has to be extended to include non-local self-energy effects even for rather 3D-like systems. However, from our first principles calculations we empirically find the dynamical contribution to the electron self-energy (in particular the quasi-particle weight) to be largely independent of momentum when expressed in a local basis. We substantiate our {\it ab initio} results by calculations for the 3D Hubbard model within the dynamical vertex approximation. The finding that dynamical and non-local correlations are separable has important consequences for advancing theories that go beyond DMFT. I will discuss the implications on the example of our recent {\it GW}+DMFT results for SrVO$_3$. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:30PM |
Q46.00010: General interaction-induced density wave states from a symmetry perspective J.W.F. Venderbos We present a symmetry classification of particle-hole condensates, i.e. general density wave states, to show how an organization in terms of translational and point group symmetries provides immediate insight into the electronic properties of such states. We discuss site, bond and flux ordered density wave states in systems with square and hexagonal symmetry. We establish a robust connection between the transformation behavior under lattice symmetries of such density waves and the low-energy description of the electronic properties, which is independent of specific lattices and fully determined by symmetry. In addition, we show how an organization in terms of lattice symmetry is helpful in identifying and predicting electronic states matter with topological quantum numbers. For systems with hexagonal symmetry we propose a new class of time-reversal invariant spin-bond ordered density waves. We address how interactions may induce the formation of these density waves in real materials and make contact with recent works which indicate that symmetric density waves are good variational ground state candidates for interacting lattice fermion models. [Preview Abstract] |
Wednesday, March 5, 2014 4:30PM - 4:42PM |
Q46.00011: Hole binding in Mott antiferromagnets: A DMRG study Zheng Zhu, Hong-Chen Jiang, D.N. Sheng, Zheng-Yu Weng The binding of injected holes in antiferromagnets is studied based on the density matrix renormalization group (DMRG) simulation for the t-J model on square ladders. It is shown that the binding strength is substantially enhanced in a spin background with a short-range spin correlation, in contrast to that with a quasi-long-range spin correlation. However, it is further found that the enhanced pairing strength diminishes once the phase string effect in the hopping term of the t-J ladders is switched off and a coherent quasiparticle behavior is restored for an unpaired single hole. General implications for the nature of pairing in doped Mott insulators will be also discussed. [Preview Abstract] |
Wednesday, March 5, 2014 4:42PM - 4:54PM |
Q46.00012: Wave-function Localization and Impurity-induced First Order Phase Transition in Correlated Liquids Near the Thermal Freezing Point Shahriar Shadkhoo, Robijn Bruinsma A quantum mechanical impurity coupled to an ohmic charged liquid near the crystallization phase transition, can stabilize a local cluster in the liquid. A nonlinear free energy functional is borrowed from Landau-Brazovskii (LB) model; the theory of weak crystallization, where in Gaussian approximation and near the thermal freezing point, the correlation of fluctuations with a characteristic wave vector $q_0$ diverges, hence a crystal with unit cells of the size $q_0^{-1}$ forms. Adding nonlinearities to the free energy, however, opens up a gap in density field (order parameter) across the transition, implying a first order phase transition. We apply the instanton technique to study the first order local phase transition of the charged field from liquid to crystalline phase, induced by the impurity. We demonstrate that the particle, can stabilize the metastable minimum of the free energy slightly above the actual transition point, and facilitate the local transition. [Preview Abstract] |
Wednesday, March 5, 2014 4:54PM - 5:06PM |
Q46.00013: Exploring superconductivity in multi-orbital systems Zi Yang Meng, Hae-Young Kee, Yong Baek Kim We study possible unconventional superconducting states in correlated electronic systems with multi-orbital and strong spin-orbit coupling. In particular we focus the interplay between electronic correlation, spin-orbital coupling and lattice structure in determining a pairing symmetry. To study such systems in a controlled manner, we develop a dynamical mean field theory simulation with hybridization expansion continuous time quantum Monte Carlo impurity solver. We further explore the Parquet formalism in which the momentum dependence of the pairing vertex is explicitly introduced by combining both particle-particle and particle-hole channel contributions, to capture the pairing symmetry. The effects of hole and electron doping will be also discussed. [Preview Abstract] |
Wednesday, March 5, 2014 5:06PM - 5:18PM |
Q46.00014: Chiral sp-orbital paired superfluid of fermionic atoms in a 2D spin-dependent optical lattice Bo Liu, Xiaopeng Li, Biao Wu, W. Vincent Liu Recent progress in realizing synthetic quantum orbital materials in chequerboard and hexagonal optical lattices opens an avenue towards exploiting unconventional quantum states, advancing our understanding of correlated quantum matter. Here, we unveil a chiral $sp$-orbital paired superfluid state for an interacting two-component Fermi gas in a 2D spin-dependent optical lattice. Surprisingly, this novel state is found to exist in a wide regime of experimentally tunable interaction strengths. The coexistence of this chiral superfluid and the ferro-orbital order is reminiscent of that of magnetism and superconductivity which is a long-standing issue in condensed matter physics. The topological properties are demonstrated by the existence of gapless chiral fermions in the presence of domain wall defects, reminiscent of quantum Hall edge states. Such properties can be measured by radio frequency spectroscopy in cold atomic experiments. [Preview Abstract] |
Wednesday, March 5, 2014 5:18PM - 5:30PM |
Q46.00015: Ab initio investigation of ground state magnetic and ferroelectric properties of monoclinic CuCl$_{2}$ multiferroic system Ambesh Dixit Materials with simultaneous magnetic and ferroelectric ordering are getting attentions and are widely investigated to understand the strong lattice-charge-spin coupling in these systems. Also, the strong coupling among different degree of freedoms in these systems may give rise to the novel magnetoelectric phenomenon. Recent experimental studies on monoclinic CuCl$_{2}$ system suggest that system undergoes antiferromagnetic transition $\sim$ 25 K in conjunction with ferroelectric ordering simultaneously. The helimagnetic ordering of Cu ions (S $=$ 1/2 ) along c-axis causes the onset of ferroelectric ordering along b-axis, breaking spatial inversion symmetry. We investigated the ground state magnetic and ferroelectric properties of copper chloride in its monoclinic structure (space group C2/m) using density functional theory. The spin dependent calculations are carried out to understand the magnetic structure and ferroelectric polarization was calculated along different axis. The correlation of magnetic structure and the onset of polarization in CuCl$_{2}$ system will be discussed in the context of magnetoelectric coupling in this system. [Preview Abstract] |
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