Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session T22: Strongly Correlated Electron Theory III |
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Sponsoring Units: DCMP Chair: Adrian del Maestro, University of Vermont Room: 324 |
Thursday, March 21, 2013 8:00AM - 8:12AM |
T22.00001: Lifshitz Transition in the Two Dimensional Hubbard Model Kuang-Shing Chen, Ziyang Meng, Thomas Pruschke, Juana Moreno, Mark Jarrell Using large-scale dynamical cluster quantum Monte Carlo simulations, we study the Lifshitz transition of the two dimensional Hubbard model with next-nearest-neighbor hopping ($t'$), chemical potential and temperature as control parameters. At $t'\le0$, we identify a line of Lifshitz transition points associated with a change of the Fermi surface topology at zero temperature. In the overdoped region, the Fermi surface is complete and electron-like; across the Lifshitz transition, the Fermi surface becomes hole-like and develops a pseudogap. At (or very close to) the Lifshitz transition points, a van Hove singularity in the density of states crosses the Fermi level. The van Hove singularity occurs at finite doping due to correlation effects, and becomes more singular when $t'$ becomes more negative. The resulting temperature dependence on the bare $d$-wave pairing susceptibility close to the Lifshitz points is significantly different from that found in the traditional van Hove scenarios. [Preview Abstract] |
Thursday, March 21, 2013 8:12AM - 8:24AM |
T22.00002: Density Matrix Embedding Theory of Strongly Correlated Models Qiaoni Chen, Gerald Knizia, Garnet Kin-Lic Chan We apply the recently developed density matrix embedding theory(DMET), to the honeycomb Hubbard model and the cuprate p-d model. DMET is based on the density matrix rather than the Green's function, thus all computations are frequency independent and of much lower cost than in DMFT. In DMET large clusters can be treated with similar accuracy but lower cost than in DMFT. (i) In the honeycomb Hubbard model, QMC calculations suggested a spin-liquid between a metal and insulator, but suffered from potential finite size errors. Using cluster DMET we find only a second-order phase transition near $U=3.3$ between the metal and insulator, with no spin-liquid. Our thermodynamic data allows direct comparison to QMC calculations, highlighting the finite size errors. (ii) Three band model calculations with large cluster DMFT are infeasible, however cluster DMET calculations are very affordable. Earlier DMFT calculations place the metal-insulator transition at an unphysical d-occupancy. Using cluster DMET treatments, we show that the transition between metal and insulator shifts into the physical regime due to our ability to include large cluster correlations. [Preview Abstract] |
Thursday, March 21, 2013 8:24AM - 8:36AM |
T22.00003: Diagrammatic Monte Carlo for Fermions with Spin-Dependent Hopping Anisotropy Jan Gukelberger, Evgeny Kozik, Lode Pollet, Kris Van Houcke, Nikolay Prokof'ev, Boris Svistunov, Matthias Troyer We study attractively interacting fermions on a square lattice whose Fermi surfaces exhibit a spin-dependent anisotropy. Such a system was proposed to harbor several exotic phases, most notably a Cooper-pair Bose-metal featuring a gap for fermionic excitations but gapless, uncondensed pair excitations along a Bose surface in momentum space. We present unbiased numeric results obtained with Diagrammatic Monte Carlo, a new technique for correlated fermionic systems based on sampling Feynman diagrammatic series directly in the thermodynamic limit. For the relevant regime of intermediate coupling strength our data show that the Fermi surface mismatch indeed suppresses the BCS transition to superfluidity. At strong anisotropy we find no sign of an ordering transition down to very low temperature suggesting existence of a quantum-phase transition from the conventional superconductor to an uncondensed state driven by the Fermi surface anisotropy. [Preview Abstract] |
Thursday, March 21, 2013 8:36AM - 8:48AM |
T22.00004: Non-Equilibrium Conductivity at Quantum Critical Points Andrew Berridge, M.J. Bhaseen, A.G. Green The behaviour of quantum systems driven out of equilibrium is a field in which we are still searching for general principles and universal results. Quantum critical systems are useful in this search as their out of equilibrium steady states may inherit universal features from equilibrium. While this has been shown in some cases, the calculational techniques used often involve simplified models or calculational tricks, which can obscure some of the underlying physical processes. Here we use a Boltzmann transport approach to study the steady-state non-equilibrium properties - conductivity and current noise, of the Bose-Hubbard model head-on. We must explicitly consider heat-flow and rate limiting processes in the establishment of the steady-state to show that it can indeed be universal. Our analysis reveals the importance of the hydrodynamic limit and the limitations of current approaches. [Preview Abstract] |
Thursday, March 21, 2013 8:48AM - 9:00AM |
T22.00005: Quantum criticality of reconstructing Fermi surfaces Junhyun Lee, Philipp Strack, Subir Sachdev We present a functional renormalization group analysis of a quantum critical point in a two-dimensional metal involving Fermi surface reconstruction due to the onset of spin density wave order. The critical theory is controlled by a fixed point in which the order parameter and fermionic quasiparticles are strongly coupled, and acquire spectral functions with a common dynamic critical exponent. We obtain results for critical exponents, and for the variation in the quasiparticle spectral weight around the Fermi surface. [Preview Abstract] |
Thursday, March 21, 2013 9:00AM - 9:12AM |
T22.00006: Electric polarization in correlated insulators Reza Nourafkan, Gabriel Kotliar We derive a formula for the electric polarization of interacting insulators, expressed in terms of the full Green's functions of the system. We use the formula to investigate changes in the electric polarization of the half-filled ionic Hubbard model. Correlations work in favor of covalency and a small lattice deformation can trigger substantial changes in the electric polarization. At the onset of the anti-ferromagnetic phase, a small lattice distortion suppresses the staggered magnetization and simultaneously the electric polarization has a higher variation. This behavior is absent when the anti-ferromagnetic phase is fully established. We also find that the quasi-particle approximation is a reliable approximation for weak to intermediate interaction strengths. [Preview Abstract] |
Thursday, March 21, 2013 9:12AM - 9:24AM |
T22.00007: Multiple energy scales and emerging quasiparticles in a doped Mott insulator Wenhu Xu, Gabriel Kotliar We recognize two temperature scales relevant to formation of quasiparticles but distinct from the Brinkman-Rice scale in a doped Mott insulator. $T_{qp}$ marks the formation of incoherent quasiparticles, while a smaller scale $T_{FL}$ indicates the onset of Fermi-liquid coherence. Below $T_{qp}$, the scattering rate evolves linearly with temperature and the quasiparticle weight is also strongly $T$-dependent. Furthermore, the imaginary part of self energy is particle-hole asymmetric at low energy. These facts lead to non-Fermi liquid behaviors in transport properties. The Fermi liquid scale $T_{FL}$ is characterized by a smooth saturation of quasiparticle weight and emerging particle-hole symmetry in self energy. We compute transport properties and find that non-Fermi liquid behavior of longitudinal and Hall resistivity persist down to well below $T_{FL}$ while Hall angle and Nernst effect have revealed Fermi-liquid behavior above $T_{FL}$. We also discuss the validity of relaxation time approximation in interpreting non-Fermi liquid behaviors. [Preview Abstract] |
Thursday, March 21, 2013 9:24AM - 9:36AM |
T22.00008: Strongly enhanced thermal transport in a lightly doped Mott insulator Veljko Zlatic, Jim Freericks We discuss the charge and heat transport of a ``bad metal'' described by the Falicov-Kimball model near half-filling, using DMFT. For a lightly doped Mott insulator, the exact solution gives transport coefficients of a universal form at low, $T\leq T_0$, and high temperatures, $T\geq T_\mu$. These characteristic temperatures are such that, for $T\leq T_0$, transport is not affected by the excitations across the gap and that, for $T\geq T_\mu$, the chemical potential is at the center of the gap. At intermediate temperatures, $T_0\leq T\leq T_\mu$, the chemical potential moves in the gap and the Wiedemann-Franz law doesn't hold. Here, the increased asymmetry of the electron and hole currents can very much enhance the thermopower S(T) and the figure of merit ZT. At a small doping and U$\gg$1 we find ZT$\geq$100. Above $T_\mu$, the electron-hole symmetry is restored and S(T) drops to small values. For U$>$1 and moderate doping, there is a broad temperature interval in which ZT$>$1, even though the electronic thermal conductivity and the effective Lorenz number are not small. In this regime, the phonons might be less adverse to ZT. Large ZT is also obtained for a three-dimensional cubic lattice. Similar effects could not be obtained with non-interacting electrons or a Fermi liquid. [Preview Abstract] |
Thursday, March 21, 2013 9:36AM - 9:48AM |
T22.00009: Strongly Correlated Transport in the Falicov Kimball Model Greg Boyd, Jim Freericks, Veljko Zlatic Many materials like the cuprates, heavy fermions, and strongly correlated oxides, are non-Fermi liquid ``bad metals'', with linear or quasi-linear resistivity as a function of temperature. The low-energy excitations are quasiparticle-like near the Fermi surface, but their lifetimes are short, so they are not coherent or free-particle-like, as in conventional Fermi-liquids (whose quasi-particle lifetimes diverge at the Fermi energy). It turns out that this kind of behavior is ubiquitous in a wide range of different strongly correlated models, as long as the temperature is above the Fermi-liquid scale. To illustrate this, we investigate the strongly correlated transport in the Falicov-Kimball model using dynamical mean-field theory (DMFT) -- which is exactly solvable in the limit of infinite coordination number. We show results for the resistivity as a function of temperature, the quasiparticle lifetime, and the spectral function. These results are quite similar to those recently found for the Hubbard model, illustrating that this high temperature behavior is seen in many different models of strong electron correlations. [Preview Abstract] |
Thursday, March 21, 2013 9:48AM - 10:00AM |
T22.00010: Charge density wave melting in a correlated system: real-time dynamics in the Hubbard-Holstein model Brian Moritz, Cheng-Chien Chen, Thomas P. Devereaux, Michel van Veenendaal Strongly correlated materials exhibit an intricate interplay between multiple degrees of freedom that can lead to competing phases with distinct broken symmetry. We study this interplay via the real-time dynamics in the photo-induced melting of the charge density wave state of the Hubbard-Holstein model. Using small cluster sparse matrix exact diagonalization and Krylov subspace techniques, we simulate the temporal evolution of the many-body wavefunction to reveal both the charge and lattice dynamics as a function of electron-electron and electron-phonon interaction strength. We study the behavior in proximity of the transition to the competing antiferromagnetic phase and comment on the character of the photo-induced transient state. [Preview Abstract] |
Thursday, March 21, 2013 10:00AM - 10:12AM |
T22.00011: Variational Monte Carlo Study of Heisenberg Model in Honeycomb Lattice with Six Spin Interactions Niladri Sengupta, Sandeep Pathak, Ka-Ming Tam, Juana Moreno, Mark Jarrell We investigate the possible nature of the spin liquid phase proposed by Quantum Monte Carlo simulation on the Hubbard model in a Honeycomb lattice. We consider the effective spin half Heisenberg model including the nearest neighbors, next nearest neighbors and six sites exchange interactions. Variational Monte Carlo simulations are performed by using the Gutzwiller projected BCS or resonating valence bond wavefunction. Different kind of symmetries (s,p+ip,d,d+id) in the pairing function are considered in order to investigate the effects of higher order exchange interactions. [Preview Abstract] |
Thursday, March 21, 2013 10:12AM - 10:24AM |
T22.00012: Representing vertex function in inhomogeneous frequency grid and its application in parquet formalism Ka-Ming Tam, Shuxiang Yang, Juana Moreno, Mark Jarrell Representing two-particle vertices has always been a central issue in computational many body methods such as the parquet formalism, a self-consistent two-particle field theory. Despite the great effort over the past two decades, its application is very limited. This is predominately due to two crucial factors--the stability of the iteration and the size of the memory allocation for representing the vertex. We previously demonstrated that the stability problem may be alleviated by explicitly restoring the crossing symmetry, making simulations beyond weak coupling for the Hubbard model feasible [1,2]. The next step for the practical applications of parquet formalism is to compress the memory required to represent the vertex. In this work, we elaborate a scheme which invokes an inhomogeneous frequency grid replacing the homogeneous Matsubara frequency grid, and thereby reducing the memory by over a order of magnitude. This may represent a crucial step towards the practical applications of the parquet formalism for large cluster sizes.\\[4pt] [1] S. X. Yang, H. Fotso, J. Liu, T. A. Maier, K. Tomko, E. F. D'Azevedo, R. T. Scalettar, T. Pruschke, M. Jarrell, Phys. Rev. E 80, 046706 (2009).\\[0pt] [2] K.-M. Tam, H. Fotso, S.-X. Yang, T.-W. Lee, J. Moreno, J. Ramanujam, M. Jarrell, arXiv:1108.4926 [Preview Abstract] |
Thursday, March 21, 2013 10:24AM - 10:36AM |
T22.00013: Effect of Electron-Phonon Interaction Range for a Half-Filled Band in One Dimension Martin Hohenadler, Fakher Assaad, Holger Fehske We demonstrate that fermion-boson models with nonlocal interactions can be simulated at finite band filling with the continuous-time quantum Monte Carlo method. We apply this method to explore the influence of the electron-phonon interaction range for a half-filled band in one dimension, covering the full range from the Holstein to the Fr\"ohlich regime. The phase diagram contains metallic, Peierls, and phase-separated regions. Nonlocal interactions suppress the Peierls instability, and thereby lead to almost degenerate power-law exponents for charge and pairing correlations. [Preview Abstract] |
Thursday, March 21, 2013 10:36AM - 10:48AM |
T22.00014: ABSTRACT WITHDRAWN |
Thursday, March 21, 2013 10:48AM - 11:00AM |
T22.00015: Fluctuation-induced pair density wave state in itinerant ferromagnets near to quantum criticality Andrew G. Green, Gareth Conduit, Christopher P. Pedder Magnetic fluctuations near to itinerant ferromagnetic quantum criticality can have profound effects. It has long been realised - since the understanding of superfluidity in helium-3 - that ferromagnetic fluctuations can drive p-wave superconductivity. Near to quantum criticality, fluctuations lead to characteristic scaling with temperature and, ultimately, to a reconstruction of the phase diagram by the fluctuation-driven formation of spatially modulated magnetic order. Here, we show that near to the putative quantum critical point, these two effects become intertwined leading to a fluctuation-driven pair density wave. Moreover, describing this physics from the quantum order-by-disorder perspective reveals a fundamentally common origin of the two effects. [Preview Abstract] |
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