Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z25: Hubbard and Other Models: Theory |
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Sponsoring Units: DCMP Room: 203B |
Friday, March 6, 2015 11:15AM - 11:27AM |
Z25.00001: The 2D Hubbard Model: Diagrammatic Extensions from Two-Particle Vertex Functions James LeBlanc, Emanuel Gull There are now a number of approaches to computing self energies at finite temperatures in the 2D Hubbard model. The dynamical mean field theory, and finite cluster extensions such as the dynamical cluster approximation (DCA), has typically provided an excellent image of local properties of correlated systems. However, towards low temperatures finite size effects occur due to the neglect of non-local correlations beyond the length scale of the impurity cluster. We explore one proposal to mitigate this effect by simulating on the two-particle level. By computing the full and two-particle irreducible vertex functions from DCA we present a first quantitative description on the reliability of this approach and compare against existing large cluster DCA results. [Preview Abstract] |
Friday, March 6, 2015 11:27AM - 11:39AM |
Z25.00002: Antiferromagnetism, Superconductivity and Pseudogap of the 2D Hubbard Model Xi Chen, Emanuel Gull, James LeBlanc The phase diagram of the two-dimensional Hubbard model in the strongly correlated regime captures some important features that have been observed in high Tc cuprate superconductors such as superconductivity and pseudogap states. We study the model on a square lattice using dynamical mean field theory and dynamical cluster approximation at various doping, temperature and next nearest neighbor hopping. By measuring the two-particle correlation functions we are able to extend beyond previous work to determine the antiferromagnetic and d-wave superconducting phase transition temperatures. Further, the pseudo gap crossover is estimated by the density of states obtained via analytic continuation, and also from the imaginary time Green's function. We will discuss the relation between pseudo gap and superconductivity based on the simulation results. [Preview Abstract] |
Friday, March 6, 2015 11:39AM - 11:51AM |
Z25.00003: Strongly-correlated electrons on the 1/5-depleted square lattice Hubbard model Ehsan Khatami, Rajiv. R. P. Singh, Warren E. Pickett, Richard T. Scalettar We study the single-orbital Hubbard model on the 1/5-depleted square lattice geometry, which arises in the spin-gap magnetic insulator CaV$_4$O$_9$ and ordered-vacancy iron selenides, presenting new issues regarding the origin of both magnetic ordering and superconductivity in these materials. We find a rich phase diagram that includes a plaquette singlet phase, a dimer singlet phase, a Neel and a block-spin antiferromagnetic phase, and stripe phases. Quantum Monte Carlo simulations show that, interestingly, the dominant pairing correlations at half filling change character from d-wave in the plaquette phase to extended s-wave upon transition to the Neel phase. These results have intriguing connections to properties of iron-based superconductors. E. Khatami, R. R. P. Singh, W. E. Pickett, and R. T. Scalettar, Phys. Rev. Lett. 113, 106402 (2014) [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:03PM |
Z25.00004: Cluster dynamical mean-field theory study of Mott transition in the triangular lattice Hubbard model Hung Dang, Xiao Yan Xu, Kuang-Shing Chen, Zi Yang Meng, Stefan Wessel In strongly correlated electron systems, geometric frustration can significantly affect the Mott metal-insulator transition. Using the dynamical cluster approximation, a cluster extension of the dynamical mean-field theory, we examine the evolution of the metal-insulator transition phase boundary as a function of temperature and interaction strength for the anisotropic triangular lattice Hubbard model as the degree of geometric frustration varies. We show that (i) the slope of this phase boundary changes systematically along with the frustration, and (ii) there exists a critical frustration at which this phase boundary is vertical. We discuss in details the connection between this critical degree of frustration and the suppression of the antiferromagnetic order due to frustration, which may be related to the emergence of exotic insulator phases as observed in several organic charge transfer salts. [Preview Abstract] |
Friday, March 6, 2015 12:03PM - 12:15PM |
Z25.00005: ABSTRACT WITHDRAWN |
Friday, March 6, 2015 12:15PM - 12:27PM |
Z25.00006: ABSTRACT WITHDRAWN |
Friday, March 6, 2015 12:27PM - 12:39PM |
Z25.00007: Mott metal-insulator transition in a metallic liquid -- Gutzwiller molecular dynamics simulations Kipton Barros, Gia-Wei Chern, Cristian D. Batista, Joel D. Kress, Gabriel Kotliar Molecular dynamics (MD) simulations are crucial to modern computational physics, chemistry, and materials science, especially when combined with potentials derived from density-functional theory. However, even in state of the art MD codes, the on-site Coulomb repulsion is only treated at the self-consistent Hartree-Fock level. This standard approximation may miss important effects due to electron correlations. The Gutzwiller variational method captures essential correlated-electron physics yet is much faster than, e.g., the dynamical-mean field theory approach. We present our efficient Gutzwiller-MD implementation. With it, we investigate the Mott metal-insulator transition in a metallic fluid and uncover several surprising static and dynamic properties of this system. [Preview Abstract] |
Friday, March 6, 2015 12:39PM - 12:51PM |
Z25.00008: Quantum electrodynamical time-dependent density functional theory for many-electron systems on a lattice Mehdi Farzanehpour, Ilya Tokatly We present a rigorous formulation of the time-dependent density functional theory for interacting lattice electrons strongly coupled to cavity photons. We start with an example of one particle on a Hubbard dimer coupled to a single photonic mode, which is equivalent to the single mode spin-boson model or the quantum Rabi model. For this system we prove that the electron-photon wave function is a unique functional of the electronic density and the expectation value of the photonic coordinate, provided the initial state and the density satisfy a set of well defined conditions. Then we generalize the formalism to many interacting electrons on a lattice coupled to multiple photonic modes and prove the general mapping theorem. We also show that for a system evolving from the ground state of a lattice Hamiltonian any density with a continuous second time derivative is locally $v$-representable. [Preview Abstract] |
Friday, March 6, 2015 12:51PM - 1:03PM |
Z25.00009: Renormalization Group Analysis of the Dissipative Quantum-XY Model Changtao Hou, Vivek Aji, Chandra Varma The action for the dissipative quantum XY model has been transformed into an action for two kinds of topological excitations, vortices and warps, and has been partially analyzed. We continue further analysis of the model to find correspondences with the solution for the phase diagram and the correlation functions of the original model by quantum Monte Carlo calculations. [Preview Abstract] |
(Author Not Attending)
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Z25.00010: Spontaneous Breaking of $U(N)$ symmetry in invariant Matrix Models Fabio Franchini Matrix Models have a strong history of success in describing a variety of situations, from nuclei spectra to conduction in mesoscopic systems, from strongly interacting systems to various aspects of mathematical physics. Traditionally, the requirement of base invariance has lead to a factorization of the eigenvalue and eigenvector distribution and, in turn, to the conclusion that invariant models describe extended systems. I will show that deviations of the eigenvalue statistics from the Wigner-Dyson universality induce an effect on the eigenvectors and that the phase transition observed when the eigenvalue density become disconnected correspond to a breaking of the $U(N)$ symmetry to a smaller one. This spontaneous symmetry breaking is essentially a Higgs mechanism, due to the strongly correlated nature of matrix models and opens the possibility to a variety of applications. [Preview Abstract] |
Friday, March 6, 2015 1:15PM - 1:27PM |
Z25.00011: Free fermion description of a paramagnetic Mott insulator Johan Nilsson A scheme is presented that enables a description of a paramagnetic Mott insulator in terms of free fermions. The main idea is to view the physical fermions as a part of a multi-band system and to allow for a correlation between the physical fermions and the auxiliary ones. Technically this is implemented through a non-linear canonical transformation, which is conveniently formulated in terms of Majorana fermions. The transformed Hamiltonian is in the next stage approximated with a free fermion theory. The approximation step is variational and provides an upper bound on the ground state energy at zero or the Free energy at finite temperature. In this way we are able to extend the domain of applicability of mean field theory and free fermions. [Preview Abstract] |
Friday, March 6, 2015 1:27PM - 1:39PM |
Z25.00012: Projector Monte Carlo Study of a 2D Fermionic Ring Exchange Only Model Katharine Hyatt, Bryan Clark, Matthew Fisher There has been significant recent interest in understanding non-Fermi liquid phases and searching for candidate Hamiltonians which may support them. DMRG and variational Monte Carlo students on 2-leg ladders have suggested the presence of such a phase, the $d$-wave metal, in certain regime of the $t-J-K$ model on the 2D square lattice. $K$ is a nearest neighbor ring exchange term. Non-variational quantum Monte Carlo studies of this model are hampered by the presence of a fermionic sign problem over most of the parameter space. However, in the $t=J=0$ limit, where only ring exchange occurs, the Hamiltonian is sign problem free. Using Green's function Monte Carlo, we investigate the phase diagram of this ring exchange only fermionic model and report our results. [Preview Abstract] |
Friday, March 6, 2015 1:39PM - 1:51PM |
Z25.00013: M\"{o}bius molecules and fragile Mott insulators Lukas Muechler, Joseph Maciejko, Titus Neupert, Roberto Car Motivated by the concept of M\"obius aromatics in organic chemistry, we extend the recently introduced concept of fragile Mott insulators (FMI) to ring-shaped molecules with repulsive Hubbard interactions threaded by a half-quantum of magnetic flux ($hc/2e$). In this context, a FMI is the insulating ground state of a finite-size molecule that cannot be adiabatically connected to a single Slater determinant, i.e., to a band insulator, provided that time-reversal and lattice translation symmetries are preserved. Based on exact numerical diagonalization for finite Hubbard interaction strength $U$ and existing Bethe-ansatz studies of the one-dimensional Hubbard model in the large-$U$ limit, we establish a duality between Hubbard molecules with $4n$ and $4n+2$ sites, with $n$ integer. A molecule with $4n$ sites is an FMI in the absence of flux but becomes a band insulator in the presence of a half-quantum of flux, while a molecule with $4n+2$ sites is a band insulator in the absence of flux but becomes an FMI in the presence of a half-quantum of flux. Including next-nearest-neighbor-hoppings gives rise to new FMI states that belong to multidimensional irreducible representations of the molecular point group, giving rise to a rich phase diagram. Reference: arXiv:1409.6732 [Preview Abstract] |
Friday, March 6, 2015 1:51PM - 2:03PM |
Z25.00014: Controlled superfluid pairing symmetry of repulsively interacting three-component fermionic atoms in optical lattices Sei-ichiro Suga We investigate the pairing symmetry of the superfluid state in repulsively interacting three-component (colors) fermionic atoms in optical lattices. When two of the three color-dependent repulsions are much larger than the other, pairing symmetry is an extended s wave although the superfluid state appears adjacent to the paired Mott insulator in the phase diagram [1]. As the difference between the three repulsions is decreased in square optical lattices, the extended s-wave pairing changes into a nodal s-wave pairing, a d$_{xy}$-wave pairing, and then into a d$_{x2-y2}$-wave pairing. This change in pairing symmetry is attributed to the competition among the density fluctuations of unpaired atoms, the quantum fluctuations of the color-density wave, and those of the color-selective antiferromagnet [2]. This phenomenon can be studied in $^{6}$Li atoms and $^{171}$Yb-$^{173}$Yb mixtures in optical lattices using existing experimental techniques.\\[4pt] [1] K. Inaba and S. Suga, \textit{Phys. Rev. Lett.} \textbf{108} (2012) 255301.\\[0pt] [2] K. Inaba and S. Suga, arXiv:1408.6582. [Preview Abstract] |
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