Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W46: Interacting Electron Systems: Theory |
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Sponsoring Units: DCMP Chair: Sergey Pershoguba, University of Maryland Room: Mile High Ballroom 4E |
Thursday, March 6, 2014 2:30PM - 2:42PM |
W46.00001: Universal Conductance of Quantum Multiwire Junctions with Entanglement Renormalization Ya-Lin Lo, Yun-Da Hsieh, Chang-Yu Hou, Pochung Chen, Ying-Jer Kao We study the universal conductance of quantum multiwire junctions via muti-scale entanglement renormalization ansatz (MERA). MERA, in its scale invariant from, provides an efficient way to extract scaling operators and scaling dimensions for both bulk and boundary conformal field theories. By utilizing the key relationship between the conductance tensor and ground-state correlation function, the universal conductance can be evaluated within the framework of boundary MERA. In particular, we study the Kane and Fisher fixed point of two interacting wires with an impurity. We demonstrate how to construct boundary MERA to estimate the current-current correlation function and scaling dimensions. We show that the universal behavior of the junction can be clearly identified within MERA. This show the grand potential of using boundary MERA to classify the fixed points of the general multiwire junctions. [Preview Abstract] |
Thursday, March 6, 2014 2:42PM - 2:54PM |
W46.00002: ABSTRACT MOVED TO Q29.00011 |
Thursday, March 6, 2014 2:54PM - 3:06PM |
W46.00003: Coupling localized spins with free fermions - A model for magnetic interfaces Rubem Mondaini, Thereza Paiva, Richard Scalettar The study of transport and magnetism in surfaces is a topic of intense research and with potential applications to several materials as manganites and $Cu/CuO$ interfaces. We study a model in which an insulating magnetic material described by a collection of localized spins couples to a metallic region. For this we introduce a stacking of antiferromagnetic spin planes on top of free-fermion planes. The interaction of the spins with the free fermions is tuned and several fermionic and spin observables are calculated in a vast region of temperatures. To obtain it, the phase space of spin configurations is spanned by a usual Metropolis algorithm and allows us to have exact values for fermionic quantities, both magnetic and transport ones, at each of the visited configurations. We observed that the increase of this interaction not only helps in localizing the fermions in the adjacent plane but turns the magnetic order in the localized spin plane more robust by increasing its critical temperature when Ising spins are considered. On the situation this coupling is large, the more distant fermionic planes start to lose connection with the rest of the system and the information regarding magnetic ordering is not propagated in the free region. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:18PM |
W46.00004: Phase transitions in the two-dimensional electron-hole gas Roman Kezerashvili, Oleg Berman, Klaus Ziegler For a gas of spatially separated electrons and holes with tunable Coulomb interaction and variable density a first order phase transition between a Bardeen-Cooper-Schrieffer (BCS) phase and an insulating Mott phase is predicted. The phase diagram is obtained in the framework of a BCS-like mean-field approach and a Landau expansion in terms of the pairing order parameter. This phase diagram indicates several phases and phase transitions, including an electron-hole plasma at low density and weak interaction, an intermediate BCS phase with Cooper pairs and an electron-hole plasma at high density and weak interaction. The insulating Mott phase appears for the strong interaction and low temperatures. The possibilities to realize these phases in realistic systems such as coupled quantum wells and graphene double layers are discussed. [Preview Abstract] |
Thursday, March 6, 2014 3:18PM - 3:30PM |
W46.00005: Dynamical frustration versus kinetic enhancement with excitons in strongly correlated bilayers Louk Rademaker Recently the condensation of electron-hole pairs in semiconductor bilayers has been achieved. This has opened up the pursuit of exciton condensation in other layered materials. Here I will present recent theoretical work on exciton physics in complex oxide heterostructures. The poorly understood high temperature superconducting cuprates are ideal candidates for bilayer exciton condensation. Therefore we study the dynamics and the phase diagram of bilayer excitons in a Mott insulating p/n heterostructure, which shows rich exciton-spin interaction phenomena. I will discuss the dynamical frustration experienced by an exciton moving through an antiferromagnetic background. In sharp contrast, I will show how in the exciton superfluid phase the magnetic excitations 'borrow' kinetic energy from the excitons. References: L. Rademaker, K. Wu, H. Hilgenkamp and J. Zaanen, EPL 97, 27004 (2012); L. Rademaker, K. Wu and J. Zaanen, New Journ. of Phys. 14, 083040 (2012); L. Rademaker, J. van den Brink, H. Hilgenkamp and J. Zaanen, Phys. Rev. B 88, 121101(R) (2013). [Preview Abstract] |
Thursday, March 6, 2014 3:30PM - 3:42PM |
W46.00006: Entanglement Spectroscopy using Quantum Monte Carlo Chia-Min Chung, Lars Bonnes, Pochung Chen, Andreas L\"auchli We present a numerical scheme to reconstruct a subset of the entanglement spectrum of quantum many body systems using quantum Monte Carlo. The approach builds on the replica trick to evaluate particle number resolved traces of the first $n$ of powers of a reduced density matrix. From this information we reconstruct $n$ entanglement spectrum levels using a polynomial root solver. We illustrate the power and limitations of the method by an application to the extended Bose-Hubbard model in one dimension where we are able to resolve the quasi-degeneracy of the entanglement spectrum in the Haldane-Insulator phase. In general the method is able to reconstruct the largest few eigenvalues in each symmetry sector and typically performs better when the eigenvalues are not too different. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 3:54PM |
W46.00007: Dynamically Generated Gaps in Holographic Models of Interacting Fermions Garrett Vanacore, Philip Phillips Previous investigations have shown that a dynamical gap forms in the holographic theory dual to fermions interacting via a dipole (Pauli) coupling in an AdS$_{d+1}$-Reissner-N\"ordstrom background. We examine the analogous problem in an AdS$_{d+1}$-Schwarzschild geometry with a probe gauge field, finding that the gap persists. Our results suggest that bulk field interactions -- rather than emergent symmetries of the boundary theory -- are the origin of the gap. [Preview Abstract] |
Thursday, March 6, 2014 3:54PM - 4:06PM |
W46.00008: RG Analysis on a Neck-Narrowing Lifshitz Transition in the Presence of Weak Short-Range Interactions in Two Dimensions Sedigh Ghamari, Sung-Sik Lee, Catherine Kallin We present a pertrbative renormalization group (RG) analysis for a neck-narrowing Lifshitz transition in the presence of weak short-range interactions in two dimensions. The model we examine is described by the dispersion $\varepsilon(\mathbf{k}) = k_x^2-k_y^2$, which would be at the critical point of the neck-narrowing transition at zero chemical potential, $\mu=0$. At the critical point ($\mu=0$), we find that one-loop quantum corrections to the interaction vertex are non-analytic. This makes capturing the evolution of the low-energy effective theory, as the energy cutoff is progressively lowered, in terms of $\beta$-functions for local operators impossible. Thus we conjecture that any consistent RG description at the critical point of this neck-narrowing transition will involve non-local operators. Slightly away from the critical point ($\mu > 0$), where the Fermi surface has a narrow neck, we find that the quantum corrections are analytic only over a finite momentum range, which shrinks to zero as the chemical potential approaches zero. More importantly, within this analytic range, where a local RG description is possible, we show that the narrower the width of the neck, the larger the couplings of irrelevant interactions become, leading to the breakdown of perturbative RG. [Preview Abstract] |
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