Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B19: Precision Many Body Physics IIFocus
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Sponsoring Units: DCOMP DCMP Chair: Boris Svistunov, University of Massachusetts Amherst Room: BCEC 156C |
Monday, March 4, 2019 11:15AM - 11:51AM |
B19.00001: Spatial Charge and Spin Correlations in the 2D Fermi-Hubbard Model: Comparison between quantum Monte Carlo simulations and optical lattice emulators Invited Speaker: Nandini Trivedi I will report on the current status and challenges faced by quantum Monte Carlo simulations to obtain quantitative information about the spatially resolved charge and spin correlations in the two-dimensional Fermi-Hubbard model. The computational results will be compared with those obtained in site-resolved imaging experiments with fermionic atoms in optical lattices. I will also discuss results with and without a Zeeman field at a wide range of temperatures, including temperatures below currently reachable in experiments. Some of the open questions I will discuss are: (1) Are there signatures of fractionalization of the fermionic spectral function? (2) How close are we to observing d-wave superconductivity in the simulations and experiments? (3) What is the sign problem and in which regions of parameter space is it most problematic? |
Monday, March 4, 2019 11:51AM - 12:03PM |
B19.00002: Metal to insulator crossover and non-Fermi-liquid physics in the half-filled 2d Hubbard model Aaram Joo Kim, Fedor Simkovic, Evgeny Kozik We present a controlled study of the finite-temperature crossover from the metallic to insulating regime in the half-filled 2D Hubbard model using Diagrammatic Monte Carlo techniques in the thermodynamic limit. Our results for one- and two-body properties confirm absence of the metal- to-insulator transition at any non-zero coupling and relate the insulating behavior to development of extended antiferromagnetic (AFM) correlations. The crossover is marked by the AFM correlation length extending beyond one lattice constant and involves an intermediate non-Fermi-liquid regime with a partially gapped Fermi surface. We observe the peculiar behavior of thermodynamic observables at the crossover indicative of the Slater-type insulator scenario. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B19.00003: Pair Density Wave in the doped t-J model with ring exchange on triangular lattice Xiao Yan Xu, Kam Tuen Law, Patrick Lee In our former work (PRL 121 046401 (2018)), we found a quantum spin liquid with spinon Fermi surface in the two dimensional spin-1/2 Heisenberg model with four-spin ring exchange on triangular lattice. In this work we dope the spinon Fermi surface phase by studying the t-J model with four-spin ring exchange. We perform density matrix renormalization group calculations on four-leg cylinders of triangular lattice and find clear signatures of pair density wave. The pair correlation function is oscillatory, even though it decays rapidly with distance with a power law larger than 2. The doping dependence of the decay and the period are studied. This is the first example where the pairing density wave is the dominate pairing in a system without a spin gap. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B19.00004: An Auxiliary Field Quantum Monte Carlo study of the Hubbard Kanamori model Hongxia Hao, Brenda Rubenstein, Hao Shi In the eld of strongly-correlated many-electron systems, the Hubbard Kanamori model has been extensively studied as a prototype for transition-metal oxides, to accurately describe interesting problems like magnetic properties, phase transitions, and unconventional superconductivity. The model is multiorbital in nature and contains Hunds coupling terms. However, due to the sign problem, it is mainly studied in the framework of Dynamical Mean-Field Theory (DMFT). We study the model using the ground state Auxiliary Field Quantum Monte Carlo (AFQMC) method. Different decomposition strategies for the Hunds coupling and pair-exchange terms are proposed for Hubbard-Stratonovich transformation. The Constrained Path Approximation and Phaseless Approximation are used to control the sign and phase problem. Systematic tests are carried out and shown the high accuracy of this approach. The ground state properties of real material Ca2RuO4 will be discussed. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B19.00005: Study of competing phases in the half filled Hubbard-Holstein model by "sign-free" determinantal Langevin simulations Seher Karakuzu, Sandro Sorella Understanding the properties of strongly correlated models is a challenging problem since many analytical tools cannot be applied due to the complicated nature of the problems. Here, we apply numerical methods in order to investigate the ground state thermodynamic limit properties of the so-called Hubbard-Holstein model in two spatial dimensions. We show that it is possible to perform "sign-problem-free" path integration for the model at half-filling by an appropriate choice of Hubbard-Stratonovich transformation and exact integration of phononic degrees of freedom. We apply an efficient first-order accelerated Langevin dynamics algorithm to evaluate all relevant correlation functions of the model. Preliminary calculations at U/t=4 and U/t=1, ω0/t=1, indicate a strong competition of antiferromagnetic and charge-density-wave orders. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B19.00006: Hubbard model analysis with dynamical mean-field theory and selective configuration interaction Carlos Mejuto Zaera, Norm Tubman, Birgitta K Whaley The two-dimensional square lattice Hubbard model has been one of the most investigated Hamiltonian systems in condensed matter physics during the last few decades. Despite extensive efforts and numerous theoretical studies, there is still debate about its zero temperature phase diagram. Here, we present numerical results obtained using adaptive selected configuration interaction (ASCI) techniques for both finite size clusters and the thermodynamic limit, with the latter obtained by combining ASCI with dynamical mean-field theory (DMFT). We study basic spectral properties together with two-point correlation functions of spin and charge, for a variety of particle fillings and interaction strengths. Away from half-filling and for a wide range of interaction strengths, the finite size cluster results indicate that the ground state wave function presents a shell structure similar to that of atomic or molecular systems. In the bulk ASCI-DMFT calculations we study the effect of the bath discretization on the spectral properties. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B19.00007: WITHDRAWN ABSTRACT
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Monday, March 4, 2019 1:03PM - 1:15PM |
B19.00008: Recent advances in Diagrammatic Monte Carlo RICCARDO ROSSI In this talk, I will present some of the recent advances obtained in the automatic high-order computations of Feynman diagrams for fermionic systems. I will discuss in particular the Connected Determinant Monte Carlo algorithm (CDet) [1, 2] and its extensions, and I will present results for the Fermi-Hubbard model as the paradigmatic strongly-correlated fermionic system. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B19.00009: Functional renormalization group study of the three-dimensional Hubbard
model Jannis Ehrlich, Carsten Honerkamp We present the extension of the truncated unity functional renormalization |
Monday, March 4, 2019 1:27PM - 1:39PM |
B19.00010: Multiloop functional renormalization group for the two-dimensional Hubbard model: Loop convergence of the response functions Agnese Tagliavini, Cornelia Hille, Fabian B. Kugler, Sabine Andergassen, Alessandro Toschi, Carsten Honerkamp We present a functional renormalization group (fRG) study of the two dimensional Hubbard model, performed with an algorithmic implementation which lifts some of the common approximations made in fRG calculations. In particular, in our fRG flow; (i) we take explicitly into account the momentum and the frequency dependence of the vertex functions; (ii) we include the feedback effect of the self-energy; (iii) we implement the recently introduced multiloop extension which allows us to sum up all the diagrams of the parquet approximation with their exact weight. Due to its iterative structure based on successive one-loop computations, the loop convergence of the fRG results can be obtained with an affordable numerical effort. In particular, focusing on the analysis of the physical response functions, we show that the results become independent from the chosen cutoff scheme and from the way the fRG susceptibilities are computed, i.e., either through flowing couplings to external fields, or through a "post-processing" contraction of the interaction vertex at the end of the flow. The presented substantial refinement of fRG-based computation schemes paves a promising route towards future quantitative fRG analyses of more challenging systems and/or parameter regimes. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B19.00011: Ground-State Superfluid Phase Diagram of the Two-Dimensional Fermionic Hubbard Model with Next-Nearest-Neighbour Hopping Fedor Simkovic, Youjin Deng, Evgeny Kozik In this work, we employ the Bold Diagrammatic Monte Carlo method to establish the superfluid phase diagram in terms of density and interaction strength and for several values of next-nearest-neighbour hopping. We find that although a multitude of superfluid states persists up to moderate interactions the picture changes severely compared to the weak-coupling interaction limit. We investigate into how relative proximity to the Van Hove filling affects superfluid order parameters and find that this effect diminishes with increasing interaction strength. |
Monday, March 4, 2019 1:51PM - 2:03PM |
B19.00012: Superconducting paring induced by the Mott stripe in t-J ladders Chen Cheng, Rubem Mondaini, Marcos Rigol Stripe formation is ubiquitous in the doped cuprates family and in corresponding numerical studies on 2D lattices. However, the complex competition of different orders makes it difficult to understand how they precisely affect the superconducting pairing in high-temperature superconductors. Alternatively, we study a simplified ladder system with doped outer-legs and a Mott stripe core, produced by the interplay of strong repulsion and the large negative on-site potential in the inner legs. By using the density matrix renormalization group method in 4-leg ladders, we show that, for anisotropic exchange couplings, a novel singlet-pair superconducting phase occurs with the fermions in the pairs residing on different sides of the Mott insulating stripe. In this phase, the binding energy is negative and the interleg singlet-pair correlation function decays algebraically with distance, in contrast to other correlations that are exponentially decaying. We expect our findings to shed light on the pairing mechanisms for the high-temperature superconductivity, and potentially highlight novel types of pairing mechanisms in AMO experiments. Part of this work is published as Phys. Rev. B 98, 121112(R) (2018). |
Monday, March 4, 2019 2:03PM - 2:15PM |
B19.00013: Superconductivity in the Hubbard model: a hidden-order diagnostics from the Luther-Emery phase on ladders Luca Fausto Tocchio, Federico Becca, Arianna Montorsi Short-range antiferromagnetic correlations are known to open a spin gap in the repulsive Hubbard model on ladders with M legs, when M is even. We show that the spin gap originates from the formation of correlated pairs of electrons with opposite spin, captured by the hidden ordering of a spin-parity operator. Since both spin gap and parity vanish in the two-dimensional limit, we introduce the fractional generalization of spin parity and prove that it remains finite in the thermodynamic limit. Our results are based upon variational wave functions and Monte Carlo calculations: Performing a finite size-scaling analysis with growing M, we show that the doping region where the parity is finite coincides with the range in which superconductivity is observed in two spatial dimensions. Our observations support the idea that superconductivity emerges out of spin gapped phases on ladders, driven by a spin-pairing mechanism, in which the ordering is conveniently captured by the finiteness of the fractional spin-parity operator. |
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