Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C19: Precision Many Body Physics IIIFocus
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Sponsoring Units: DCOMP DCMP Chair: Evgeny Kozik, Kings Coll Room: BCEC 156C |
Monday, March 4, 2019 2:30PM - 3:06PM |
C19.00001: Quantum Monte Carlo Study of Strongly Interacting Fermi Gases in Two Dimensions: BCS-BEC Crossover, Spin-orbit Coupling, and Dynamical Response Functions Invited Speaker: Hao Shi We describe recent advances in |
Monday, March 4, 2019 3:06PM - 3:18PM |
C19.00002: "Quasielectrons in Lattice Moore–Read Models" Sourav Manna, Julia Wildeboer, Anne E. B. Nielsen Anyons are fractionally charged quasiparticles which are neither fermions nor bosons. Anyons exhibit fractional statistics and important for topological quantum computation. Anyonic Moore–Read states provides a well explored description for the insertion of quasiholes in the continuum. However, quasielectron insertion creates a singularity in the continuum state which further complicates the problem. In this work we show that the singularity problem can be avoided by placing quasielectrons in fractional quantum Hall lattice systems. We construct Moore–Read Pfaffian states for filling fraction 5/2 and incorporate quasiholes and quasielectrons. We investigate density profile, charge, size and braiding properties of the anyons by means of a Metropolis Monte Carlo simulation. Further we derive a few body parent Hamiltonian for the states. Additionally we investigate density profile, charge and shape of the anyons in the Kapit–Mueller model by employing an exact diagonalization technique. We compare our results for the analytical states with the anyons in the Kapit–Mueller model. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C19.00003: Dispersion Relation of the GMP Mode in the Nematic Phase of Fractional Quantum Hall States Umang Mehta, Dam Thanh Son We compute the dispersion relation for the GMP mode of the fractional quantum Hall effect in the nematic phase for Jain sequences at large N using Golkar, Nguyen, Roberts and Son's 'higher-spin theory' for magnetorotons. The dispersion relation is computed to all orders in the momentum expansion and is valid wherever the momentum expansion holds. It captures the magnetoroton minimum at finite momentum in the regime where the momentum expansion still holds. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C19.00004: Interacting Chern insulators: Diagrammatics well beyond the lowest order Igor Tupitsyn, Nikolai Prokof'ev We study phase diagram of the interacting spin-1/2 Haldane model with chiral phase φ=π/2 at half-filling. Both on-site and long-range Coulomb repulsive interactions (Haldane-Hubbard-Coulomb model) are considered. The problem with on-site interaction U alone was addressed in the past by a variety of approximate and finite size methods that produced results in disagreement with each other both quantitatively and qualitatively. Conventional Quantum Monte Carlo methods, capable of dealing with "reasonable" system sizes, are ineffective here due to the fermionic sign problem. We employ the Diagrammatic Monte Carlo (DiagMC) technique to (i) accurately locate topologically nontrivial phases in the (△,U)-plane (△ is the inversion symmetry breaking on-site energy) and (ii) demonstrate the strong effect of typically discarded in theoretical considerations long-range part of the Coulomb interaction. The DiagMC technique is not subject to the conventional fermionic sign problem and allows one to deal with arbitrary shape of interaction potential in an approximations free manner. Final results with controlled accuracy are obtained by computing vertex corrections from higher-order diagrams until convergence is reached. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C19.00005: Critical torus spectrum of the Gross-Neveu-Yukawa field theory Michael Schuler, Stephan Heßelmann, Seth Whitsitt, Thomas C Lang, Stefan Wessel, Andreas Läuchli We compute the low-energy critical torus spectrum of the Gross-Neveu-Yukawa universality class, which features N=4 component Dirac spinors that spontaneously break a Z2 chiral symmetry, in D=(2+1) dimensions. A possible lattice realization of such Dirac fermions is provided by the interacting t-V model of spinless fermions on the honeycomb lattice. We use a combination of Exact Diagonalization and Quantum Monte Carlo simulations to compute the energy spectrum on finite-size clusters with periodic boundaries, and perform an extrapolation to the thermodynamic limit. We show that the interaction between the spinor field and the scalar order-parameter field strongly influences the torus spectrum at the critical point, and propose the critical spectrum as a universal fingerprint of the critical Gross-Neveu-Yukawa field theory. Moreover, we estimate the renormalization of the Fermi velocity in the Dirac phase from the interaction induced corrections to the energy spectrum, and extrapolate the observed linear renormalization up to the critical point. Finally, we contrast the Fermi velocity renormalization in the spinless t-V model with the situation in the spinful Hubbard model. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C19.00006: Unconventional pairing symmetry of interacting Dirac fermions on a π-flux lattice Huaiming Guo The pairing symmetry of interacting Dirac fermions on the π-flux lattice is studied with the determinant quantum Monte Carlo and numerical linked-cluster expansion methods. The s*- (i.e., extended s-) and d-wave pairing symmetries, which are distinct in the conventional square lattice, are degenerate under the Landau gauge. We demonstrate that the dominant pairing channel at strong interactions is an unconventional ds*-wave phase consisting of alternating stripes of s*- and d-wave phases. A complementary mean-field analysis shows that while the s*- and d-wave symmetries individually have nodes in the energy spectrum, the ds* channel is fully gapped. The results represent a new realization of pairing in Dirac systems, connected to the problem of chiral d-wave pairing on the honeycomb lattice, which might be more readily accessed by cold-atom experiments. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C19.00007: ABSTRACT WITHDRAWN
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Monday, March 4, 2019 4:18PM - 4:30PM |
C19.00008: Universal Fermi-surface anisotropy renormalization for interacting Dirac fermions with long-range interactions Shaffique Adam, Jia Ning Leaw, Ho Kin Y Tang, Maxim Trushin, Fakher Assaad, Sankar Das Sarma Recent evidence suggest an intriguing universal relationship between the Fermi surface anisotropy of the non-interacting parent two-dimensional electron gas and the strongly correlated composite Fermi liquid formed in a strong magnetic field close to half-filling. Inspired by these observations, we explore more generally the question of anisotropy renormalization in interacting 2D Fermi systems. Using a recently developed [1] non-perturbative and numerically-exact projective quantum Monte Carlo simulation as well as other numerical and analytic techniques, only for Dirac fermions with long-range Coulomb interactions do we find a universal square-root decrease of the Fermi-surface anisotropy [2]. Our proposed universality can be tested in several anisotropic Dirac materials including graphene, topological insulators and organic conductors. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C19.00009: Energy scales and quasi-particle behavior of fermions in the normal state of flat-band systems Pramod Kumar, Vanhala Tuomas, Sebastiano Peotta, Paivi Torma We explore the energy scales and quasi-particle behavior in the paramagnetic normal state of the repulsive Hubbard model on the Lieb lattice. The special geometry of the Lieb lattice, a face-centered 2D square lattice, has a flat dispersion, which leads to various novel electronic phases with the inclusion of many-body interactions [1, 2]. Singularity in the density of states can lead to the breakdown of quasi-particle behavior at finite temperature. The interplay of the singularity and the interaction determine the energy scale to observe such non-Fermi liquid behavior. We address this using dynamical mean field theory (DMFT), a very well-established methodology for correlated many-body systems. We have used continuous-time quantum Monte Carlo (CTQMC), an exact impurity solver, within DMFT. We also comment on particle-hole mapping between attractive and repulsive Hubbard model with a unitary transformation and the corresponding electronic properties. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C19.00010: Bosonic Crystalline Symmetry Protected Topological Phases beyond the Group Cohomology Proposal Hao Song, Zhaoxi Xiong, Sheng-Jie Huang It is demonstrated by explicit construction that the intricate links among short-range-entangled (SRE) states across different dimensions have a vivid embodiment in the realm of symmetry protected topological (SPT) phases with crystalline symmetry. We systematically study three-dimensional bosonic topological phases protected by any space group symmetry G. We prove that these phases are classified by Hφ5(G;Z)×Hφ1(G;Z), where φ indicates g∈G acting on Z as multiplying φ(g)=±1 depending on whether orientation is preserved by g or not. The factor Hφ5(G;Z)=HBorel,φ4(G;U(1)), known as the group cohomology proposal for classifying bosonic SPT phases, corresponds to only the phases presented by some SRE 2-skeleton without presence of E8 state or its multiples (i.e., two-dimensional chiral bosonic phases characterized by quantized thermal Hall effect). The extra factor Hφ1(G;Z) describes inequivalent E8 state configurations and be easily read off directly from the international (Hermann-Mauguin) symbol for G. Moreover, our result supports the Generalized Cohomology Hypothesis in the case of crystalline symmetries. |
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