May 2017
May 1-May 10 Biao Huang, May 11-May 20 Haiyuan Zou, May 21-May 31 Zehan Li
May 17 arXiv:1705.05578 [pdf, other] Matrix product state techniques for two-dimensional systems at finite temperature Benedikt Bruognolo, Zhenyue Zhu, Steven R. White, E. Miles Stoudenmire Comments: 14 pages, 10 figures, MPS codes publicly available at this https URL Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall) The density matrix renormalization group is one of the most powerful numerical methods for computing ground-state properties of two-dimensional (2D) quantum lattice systems. Here we show its finite-temperature extensions are also viable for 2D, using the following strategy: At high temperatures, we combine density-matrix purification and numerical linked-cluster expansions to extract static observables directly in the thermodynamic limit. At low temperatures inaccessible to purification, we use the minimally entangled typical thermal state (METTS) algorithm on cylinders. We consider the triangular Heisenberg antiferromagnet as a first application, finding excellent agreement with other state of the art methods. In addition, we present a METTS-based approach that successfully extracts critical temperatures, and apply it to a frustrated lattice model. On a technical level, we compare two different schemes for performing imaginary-time evolution of 2D clusters, finding that a Suzuki-Trotter decomposition with swap gates is currently the most accurate and efficient. May 16 arXiv:1705.05381 [pdf, other] Emergence of Chiral Spin Liquids via Quantum Melting of Non-Coplanar Magnetic Orders Ciarán Hickey, Lukasz Cincio, Zlatko Papić, Arun Paramekanti Comments: 7 pages, 8 figures Subjects: Strongly Correlated Electrons (cond-mat.str-el) Quantum spin liquids (QSLs) are long-range entangled states of quantum magnets which lie beyond the Landau paradigm of classifying phases of matter via broken symmetries. A physical route to arriving at QSLs is via frustration-induced quantum melting of ordered states such as valence bond crystals or magnetic orders. Here, we show, using extensive exact diagonalization (ED) and density-matrix renormalization group (DMRG) studies of concrete SU(2) invariant spin models on honeycomb, triangular and square lattices, that chiral spin liquids (CSLs) emerge as descendants of triple-Q spin crystals with tetrahedral magnetic order and a large scalar spin chirality. Such ordered-to-CSL melting transitions may yield lattice realizations of effective Chern-Simons-Higgs field theories. Our work provides a distinct unifying perspective on the emergence of CSLs, and suggests that materials with magnetic skyrmion crystal order might provide a good starting point to search for CSLs. May 15 arXiv:1705.04450 [pdf, other] Anisotropy crossover in the frustrated Hubbard model on four-chain cylinders G. Ehlers, B. Lenz, S. R. Manmana, R. M. Noack Comments: 16 pages, 16 figures Subjects: Strongly Correlated Electrons (cond-mat.str-el) Motivated by dimensional crossover in layered organic κ salts, we determine the phase diagram of a system of four periodically coupled Hubbard chains with frustration at half filling as a function of the interchain hopping t⊥/t and interaction strength U/t at a fixed ratio of frustration and interchain hopping t′/t⊥=−0.5. We cover the range from the one-dimensional limit of uncoupled chains (t⊥/t=0.0) to the isotropic model (t⊥/t=1.0). For strong U/t, we find an antiferromagnetic insulator; in the weak-to-moderate-interaction regime, the phase diagram features quasi-one-dimensional antiferromagnetic behavior, an incommensurate spin density wave, and a metallic phase as t⊥/t is increased. We characterize the phases through their magnetic ordering, dielectric response, and dominant static correlations. Our analysis is based primarily on a variant of the density matrix renormalization group algorithm (DMRG) based on an efficient hybrid--real-momentum-space formulation, in which we can treat relatively large lattices albeit of a limited width. This is complemented by a variational cluster approximation (VCA) study with a cluster geometry corresponding to the cylindrical lattice allowing us to directly compare the two methods for this geometry. As an outlook, we make contact with work studying dimensional crossover in the full two-dimensional system.
