Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session X20: Correlated Electrons II: Theory and Computation |
Hide Abstracts |
Sponsoring Units: DCMP Room: 280 |
Friday, March 17, 2017 8:00AM - 8:12AM |
X20.00001: Anomalous Dimension of the Electrical Current in the Normal State of the Cuprates from the Fractional Aharonov-Bohm Effect Kridsanaphong Limtragool, Philip Phillips We show here that if the current in the normal state of the cuprates has an anomalous dimension, then the Aharonov-Bohm flux through a ring does not have the standard $eBA/\hbar$ form, where $A$ is the area, $B$ is the external magnetic field, and $e$ is the electric charge, but instead it is modified by a geometrical factor that depends directly on the anomalous dimension of the current. We calculate the Aharonov-Bohm flux in square and disk geometries. In both cases, the deviation from the standard result is striking and offers a fingerprint about what precisely is strange about the strange metal. [Preview Abstract] |
Friday, March 17, 2017 8:12AM - 8:24AM |
X20.00002: Finite Temperature Density Matrix Embedding Theory Chong Sun, Garnet Chan \textit{Density Matrix Embedding Theory} (DMET) provides a powerful and less expensive framework to treat strongly correlated ground-state problems in both solids and molecules, by reproducing the entanglement between the fragment and its environment at mean-field level, while the fragment is treated at a more accurate level. In this talk, I will extend the ground-state DMET to finite temperature DMET (FT-DMET), by solving both the mean-field problem and impurity problem at finite temperature $T$, and reconstructing bath orbitals from the mean-field solution. The finite temperature Lanczos algorithm as an alternative of full configuration interaction (FCI) is used to implement the impurity solver, and a cutoff is introduced to the selection of bath orbitals from the mixed mean-field solution. We assess the performance of FT-DMET by several benchmark calculations on both molecules and lattices. The results are compared to other well-established finite temperature methods, such as quantum Monte Carlo (QMC), dynamical mean-field theory (DMFT), and so forth. [Preview Abstract] |
Friday, March 17, 2017 8:24AM - 8:36AM |
X20.00003: Photoexcitations in a 1D manganite model: From quasiclassical light absorption to quasiparticle relaxations T. K\"ohler, O. Schumann, F. Biebl, S. Kramer, S. Kehrein, S. Manmana, S. Rajpurohit, M. Sotoudeh, P. Bl\"ochl We investigate 1D correlated systems following a photoexcitation by combining ab-initio methods, time-dependent matrix product state (MPS) approaches, analytical insights from linearized quantum Boltzmann equations (LBE), and molecular dynamics (MD) simulations to describe the dynamics on different time scales ranging from femto- up to nanoseconds. This is done for manganite systems in the material class Pr$_{1-x}$Ca$_x$MnO$_3$. We derive 1D ab-initio model Hamiltonians for which we compute the ground states at different values of the doping using MD simulations. At half doping, we obtain a magnetic microstructure of alternating dimers from which we derive a 1D Hubbard-type model. The dynamics is analyzed concerning the formation and lifetime of such quasiparticles via a LBE. We find that the magnetic microstructure strongly enhances the lifetime of the excitations. In this way, our work constitutes a first step to building a unifying theoretical framework for the description of photoexcitations in strongly correlated materials over a wide range of time scales, capable of making predictions for ongoing experiments investigating pump-probe situations and unconventional photovoltaics. [Preview Abstract] |
Friday, March 17, 2017 8:36AM - 8:48AM |
X20.00004: Currents and Greens functions of impurities out of equilibrium - results from inchworm Quantum Monte Carlo Qiaoyuan Dong, Andrey Antipov, Joshph Kleinhenz, Guy Cohen, Emanuel Gull We develop an unbiased impurity solver for Anderson Impurity Model, which forms a fundamental component for non-equilibrium dynamical mean field theory, using the inchworm quantum Monte Carlo method. It is capable of computing the dynamics of strongly correlated impurity problems with time dependent parameters and overcomes the dynamical sign problem in the sense that as $t$ is increased, the effort for reaching longer times increases sub-exponentially with controlled errors. We introduce a hierarchy to compute Green’s functions, spectral functions, and currents for inchworm quantum Monte Carlo and show results in both equilibrium and voltage quench cases. [Preview Abstract] |
Friday, March 17, 2017 8:48AM - 9:00AM |
X20.00005: Hypothesis testing of quantum Monte Carlo simulations Markus Wallerberger, Alexander Gaenko, Emanuel Gull The large implementation complexity of modern quantum Monte Carlo solvers makes careful testing of the algorithm as well as verification of the results an imperative. Due to their deterministic nature, traditional unit tests are unsuited for verifying probabilistic results: they are prone to false positives in the case of outliers or changes to the implementation. Therefore, Monte Carlo data are often checked by visual inspection only, which is susceptible to incomplete and non-continuous test coverage. Statistical hypothesis testing provides a non-deterministic alternative: we choose an exact result (which exists for certain limits) as the null hypothesis and compute the statistical significance score for the Monte Carlo data. Rejection or too strong acceptance of the null hypothesis then amounts to a failed test, thus providing a test criterion for both the Monte Carlo estimate and its error bars. While this does not provide a binary answer, ambiguous cases can be systematically refined by lengthening the Monte Carlo run, and the procedure lends itself to automation. We develop a testing framework and illustrate the procedure for the two-dimensional Ising model as well as for Continuous-time quantum Monte Carlo data for the single impurity Anderson model. [Preview Abstract] |
Friday, March 17, 2017 9:00AM - 9:12AM |
X20.00006: Effect of non-local interactions and correlations in two-dimensional extended Hubbard model Hanna Terletska, Tianran Chen, Emanuel Gull We study the half-filled extended Hubbard model in two dimensions using the dynamical cluster approximation on clusters large enough that finite size effects can be controlled. The model exhibits the metallic, Mott insulating and charge ordered phases under the change of control parameters (temperature T, neighbor interaction V, and local onsite interaction U). The charge ordered phase is characterized by a checkerboard arrangement of electrons with non-zero staggered density. Our results show that within the ordered phase the model exhibits vanishing scattering rate and a finite real part of the self-energy, indicating the band-insulating-like behavior. We also find that charge ordering can be suppressed by temperature and local on-site interaction, with the critical temperature depending strongly on both local U and non-local interaction V strength. We find noticeable non-local correlations and pronounced screening effects especially in the vicinity of the transition, and explore the nature of non-local interactions on ‘screening’ in detail. [Preview Abstract] |
Friday, March 17, 2017 9:12AM - 9:24AM |
X20.00007: Correlated hopping and orbital currents in a spinless fermion lattice model Hsu Liu, Darrell Schroeter We investigate the effect of correlated hopping on the stability of orbital current patterns in a Hubbard-type model. We consider spinless fermions moving on an array of square plaquettes coupled by weak hopping. We derive a pseudospin model, where the components of the pseudospin describe plaquettes with either orbital currents or charge or bond density, at fourth order in degenerate perturbation theory. This work extends the model of Pujari and Henley [PRB \textbf{80}, 085116] to fourth order in perturbation theory where correlated hopping is first present. At this order, the degeneracy between charge and orbital current order seen in their work disappears. [Preview Abstract] |
Friday, March 17, 2017 9:24AM - 9:36AM |
X20.00008: Large effects of subtle electronic correlations on the energetics of vacancies in alpha-Fe Pascal Delange, Thomas Ayral, Sergei Simak, Michel Ferrero, Olivier Parcollet, Silke Biermann, Leonid Pourovskii We apply an ab initio theoretical framework combining the density functional and dynamical mean field theories (DFT$+$DMFT) to study the effect of electronic Coulomb correlations on the vacancy formation energy if paramagnetic alphe-Fe. The calculated value using different implementations of DFT are compared, and we show that the formation energy is substantially lower than in standard density-functional calculations and in excellent agreement with experiment. The reduction is caused by an enhancement of electronic correlations at the nearest neighbors of the vacancy. This effect is explained by subtle changes in the corresponding spectral function of the d-electrons, and is linked to the reduction of coordination on these atoms. The local lattice relaxations around the vacancy are substantially increased by many-body effects, and must be consistently calculated within DFT$+$DMFT to obtain a consistent vacancy formation energy. [Preview Abstract] |
Friday, March 17, 2017 9:36AM - 9:48AM |
X20.00009: Quantum Quench of the Sachdev-Ye-Kitaev Model Julia Steinberg, Andreas Eberlein, Subir Sachdev The Sachdev-Ye-Kitaev model is a single site model containing $N$ flavors of fermions with random infinite range interactions. It is exactly solvable in the large N limit and has an emergent reparameterization symmetry in time at low temperatures and strong coupling. This leads to many interesting properties such as locally critical behavior in correlation functions and the saturation of the chaos bound proposed .We start with the generalized Sachdev-Ye-Kitaev with quadratic and quartic interactions. This Hamiltonian has the form of a 0+1d Fermi liquid and contains long-lived quasiparticles at all values of the quadratic coupling. We quench the system into a locally critical state without quasiparticles by turning off the quadratic coupling at some initial time. We numerically study the spectral function at intermediate and long times and determine the timescale in which the system loses memory of the quasiparticles. [Preview Abstract] |
Friday, March 17, 2017 9:48AM - 10:00AM |
X20.00010: Deforming the Fredkin spin chain away from its frustration-free point Khagendra Adhikari, K. S. D. Beach Salberger and Korepin have recently introduced a model of an $S=1/2$ chain in which the interactions take the form of a singlet-pair projector that is correlated with the up or down character of the spin at a third, adjacent site. The model is frustration-free, and its exactly solvable ground state is an equal-weight superposition of spin states with a Dyck word structure. The state is highly entangled, and the excitation gap closes like inverse of the chain length cubed. We introduce a generalized model that interpolates between this so-called Fredkin spin chain and the conventional antiferromagnetic quantum Heisenberg model. We present numerical results that track the properties of the system as it is tuned between the two limits. The ground state is everywhere disordered, but the entanglement and gap scaling vary. [Preview Abstract] |
Friday, March 17, 2017 10:00AM - 10:12AM |
X20.00011: Self-Learning Monte Carlo Method Junwei Liu, Yang Qi, Zi Yang Meng, Liang Fu Monte Carlo simulation is an unbiased numerical tool for studying classical and quantum many-body systems. One of its bottlenecks is the lack of general and efficient update algorithm for large size systems close to phase transition or with strong frustrations, for which local updates perform badly. In this work, we propose a new general-purpose Monte Carlo method[1], dubbed self-learning Monte Carlo (SLMC), in which an efficient update algorithm is first learned from the training data generated in trial simulations and then used to speed up the actual simulation. We demonstrate the efficiency of SLMC in a spin model at the phase transition point, achieving a 10-20 times speedup. [1]J. Liu, et al. arXiv:1610.03137 (2016) [Preview Abstract] |
Friday, March 17, 2017 10:12AM - 10:24AM |
X20.00012: Self-Learning Monte Carlo Method in Fermion Systems Huitao Shen, Junwei Liu, Yang Qi, Zi Yang Meng, Liang Fu As a new general-purpose Monte Carlo method, self-learning Monte Carlo (SLMC) has been numerically demonstrated in boson systems. In this work, we propose a new type of update algorithm, dubbed cumulative update, which could be naturally integrated into SLMC. Based on many local updates in the self-learned effective model, cumulative update efficiently proposes a global move with a high acceptance probability in the original model. Cumulative update can reduce the conventional computational cost of a full sweep $O(N^4)$ to $O(N^3)$, and also effectively reduce the auto-correlation time to be 1. We numerically show its efficiency through the well-known double-exchange model. With cumulative update, the SLMC could be several hundreds of times faster than the conventional local update method. By employing the cumulative update, SLMC can be generally used in any sign-problem-free Fermion systems and maximize the performance of Monte Carlo simulation. [Preview Abstract] |
Friday, March 17, 2017 10:24AM - 10:36AM |
X20.00013: Competition between Kondo and Josephson effects in a triangular triple quantum dot connected to normal and superconducting leads Akira Oguri, Masaya Shirotani, Yukihiro Nakata, Yoshimichi Teratani, Yoichi Tanaka We study low-energy properties of a triangle triple quantum dot (TTQD) connected to one normal and two superconducting (SC) leads, using the Wilson numerical renormalization group approach. This system has various types of quantum phases in the normal state such as the SU(4) and the $S=1$ Nagaoka-high-spin Kondo effects, depending on the electron filling [1]. The ground state evolves as additional SC leads are connected, and interesting competition between the Kondo and Cooper-pairing singlets occurs [2]. It also causes the Andreev scattering which takes place at the interface between the TTQD and normal lead. We examine how the Andreev scattering affects the quantum phase transition, in a wide range of the gate voltage $\epsilon_d$. Near half-filling, the Josephson phase $\phi$ between the two SC leads lifts an orbital degeneracy of the TTQD in a different way at $\phi \simeq 0$ and $\pi$. We also discuss the conduction-electron under-screening of the local Nagaoka high-spin state. \noindent [1] T.\ Numata, Y.\ Nisikawa, A.\ Oguri, and A.\ C.\ Hewson, PRB {\bf 80}, 155330 (2009). [2] A.\ Oguri, I. Sato, M. Shimamoto, and Yoichi Tanaka, J.\ Phys.: Conf.\ Ser.\ {\bf 592}, 012143 (2015). [Preview Abstract] |
Friday, March 17, 2017 10:36AM - 10:48AM |
X20.00014: Influence of non-local interactions on the Mott metal-insulator transition. M. Schueler, E. G. C. P. van Loon, M. I. Katsnelson, T. O. Wehling We investigate how short- and long-ranged non-local Coulomb interactions influence the metal-insulator phase boundary of the half-filled Hubbard model on square lattices and honeycomb lattices. We find that generally, non-local interactions stabilize the Fermi-liquid regime and that the phase boundary behaves linearly with infinitesimal non-local interactions. We present an upper bound for the boundary's slope. For our investigations, we use a variational principle which maps extended Hubbard models to effective purely local Hubbard models. The mapping relies on Quantum Monte Carlo solutions of the the local Hubbard model. [Preview Abstract] |
Friday, March 17, 2017 10:48AM - 11:00AM |
X20.00015: Mott physics and spin fluctuations: a unified framework Thomas Ayral, Jaksa Vučičević, Olivier Parcollet We present a formalism for strongly correlated electron systems which consists in a local approximation of the three-leg interaction vertex [1]. The vertex is self-consistently computed with a quantum impurity model with dynamical interactions in the charge and spin channels, similar to dynamical mean field theory (DMFT) approaches. The electronic self-energy and the polarization are both frequency and momentum dependent. The method interpolates between the spin-fluctuation or GW approximations at weak coupling and the atomic limit at strong coupling. We first apply the formalism to the two-dimensional Hubbard model on a square lattice. We show that as interactions are increased, the local vertex acquires a strong frequency dependence, driving the system to a Mott transition, while at low enough temperatures the momentum-dependence of the self-energy is enhanced due to large spin fluctuations. Upon doping, we find, already at the single-site impurity level, a Fermi arc in the one-particle spectral function, a signature of the pseudo-gap state. Second, we present an extension of the method to cluster impurity models. We reach close agreement with large-cluster DMFT results already with a four-site impurity cluster. [1] Phys. Rev. B 92, 115109 and Phys. Rev. B 93, 235124 [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700