Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B20: Frustration and Correlation: Theory |
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Sponsoring Units: DCMP Chair: David Parker, Oak Ridge National Laboratory Room: 280 |
Monday, March 13, 2017 11:15AM - 11:27AM |
B20.00001: Exact Solution to Interacting Kitaev Chain at Symmetric Point Jian-Jian Miao, Hui-Ke Jin, Fu-Chun Zhang, Yi Zhou Kitaev chain model with nearest neighbor interaction U is solved exactly at the symmetry point $\Delta=t$ and chemical potential $\mu=0$ in open boundary condition. By applying two Jordan-Wigner transformations and a spin-rotation, such a symmetric interacting model is mapped to a non-interacting fermion model, which can be diagonalized exactly. The solutions include topologically non-trivial phase at U$<$t and topologically trivial phase at U$>$t. The two phases are related by dualities. Quantum phase transitions in the model are studied with the help of the exact solution. [Preview Abstract] |
Monday, March 13, 2017 11:27AM - 11:39AM |
B20.00002: Staircase of crystal phases of hard-core bosons on the kagome lattice Daniel Huerga, Sylvain Capponi, Jorge Dukelsky, Gerardo Ortiz We study the quantum phase diagram of a system of hard-core bosons on the kagome lattice with nearest-neighbor repulsive interactions, for arbitrary densities, by means of the hierarchical mean-field theory and exact diagonalization techniques. This system is isomorphic to the spin S = 1/2 XXZ model in presence of an external magnetic field, a paradigmatic example of frustrated quantum magnetism. In the nonfrustrated regime, we find two crystal phases at densities 1/3 and 2/3 that melt into a superfluid phase when increasing the hopping amplitude, in semiquantitative agreement with quantum Monte Carlo computations. In the frustrated regime and away from half-filling, we find a series of plateaux with densities commensurate with powers of 1/3. The broader density plateaux (at densities 1/3 and 2/3) are remnants of the classical degeneracy in the Ising limit. For densities near half-filling, this staircase of crystal phases melts into a superfluid, which displays finite chiral currents when computed with clusters having an odd number of sites. Both the staircase of crystal phases and the superfluid phase prevail in the noninteracting limit, suggesting that the lowest dispersionless single-particle band may be at the root of this phenomenon. [Preview Abstract] |
Monday, March 13, 2017 11:39AM - 11:51AM |
B20.00003: SO($N$) Singlet Projection Model on the Kagome Lattice Matthew Block, Ribhu Kaul We explore the SO($N$)-symmetric, nearest-neighbor singlet projection model on the two-dimensional kagome lattice using a quantum Monte Carlo simulation that employs the stochastic series expansion with global loop updates. There is no sign problem with this model, which is appropriate for nonbipartite lattices. We characterize the valence bond solid (VBS) phase that emerges for sufficiently large $N$ and, by augmenting our model with either a next-nearest neighbor interaction that tends to order spins on the same sublattice, which encourages magnetic order for large $N$, or a plaquette-like interaction, which encourages VBS order for small $N$, we are able to examine the properties of the quantum phase transitions separating the two ordered phases. This work attempts to build off the success of investigations of the same SO($N$) model on the triangular lattice [Kaul, Phys. Rev. Lett. \textbf{115}, 157202] and the analogous SU($N$) model on the bipartite square, rectangular, and honeycomb lattices [Kaul and Sandvik, Phys. Rev. Lett. \textbf{108}, 137201; Block, Melko, and Kaul, Phys. Rev. Lett. \textbf{111}, 137202] where the model is a natural generalization of the SU(2), spin-1/2 Heisenberg antiferromagnet. [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B20.00004: Novel solid phase in the frustrated Kagome lattice XXZ model Guang Yu Sun, YAN QI Qin, Yan Cheng Wang, Zi Yang Meng |
Monday, March 13, 2017 12:03PM - 12:15PM |
B20.00005: Abstract Withdrawn We present a slave boson meanfield analysis of quantum spin ice. We study spin ice models on the Pyrochlore, Kagome and square lattices and we reproduce parts of their phase diagrams. We show that the meanfield supports several different spin liquids and solids. Furthermore we show that spin ice on the Pyrochlore and square lattices is equivalent to a U(1)xZ2 gauge theory which may or may not be in the confining phase depending on the parameters of the spin ice model. We show that the projective symmetry group classification applies to the square and Pyrochlore spin ice models. In particular we show that the algebraic PSG for a spin ice model is equivalent to the algebraic PSG of a bosonic spin liquid with the same IGG. We present a large N limit for these models and show the the meanfield becomes exact in this limit. We also present a large S (semiclassical limit for the spin ice model). A slave fermion meanfield is also presented for the square (planar) spin ice model. |
Monday, March 13, 2017 12:15PM - 12:27PM |
B20.00006: Mean-Field Study of MIT Suppression in Pr-227 via Rare Earth Magnetism Kyle Sherman We report on a stability study of the metal-insulator transition in the pyrochlore iridates at zero kelvin. The purpose of this study has been to determine how the insulating state may be suppressed in Pr2Ir2O7 due to the frustrated Pr magnetism. Our model incorporates itinerant Ir electrons and their correlations, spin-orbit coupling, and effects of the localized Pr spins. We have included a Kondo interaction between sub-lattices and an antiferromagnetic interaction between neighboring Pr spins. Our phase diagram demonstrates tuning among the paramagnetic, 2i2o, 3i1o, and AiAo configurations as well as a metal to insulator transition. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B20.00007: Anisotropy induces non-Fermi liquid behavior and nemagnetic order in three-dimensional Luttinger semimetals Igor Boettcher, Igor Herbut We illuminate the intriguing role played by spatial anisotropy in three-dimensional Luttinger semimetals featuring quadratic band touching and long-range Coulomb interactions. For sufficiently strong anisotropy, two main effects come to light. First, the three-dimensional system features an Abrikosov non-Fermi liquid ground state. Second, qualitatively new fixed points show up which describe quantum phase transitions into phases with nemagnetic orders -- higher-rank tensor orders that break time-reversal symmetry, and thus have both nematic and magnetic character. In real materials these phases may be realized through sufficiently strong microscopic short-range interactions. On the pyrochlore lattice, the anisotropy-induced fixed points determine the onset of all-in-all-out or spin ice ordering of local magnetic moments. [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B20.00008: Determinantal quantum Monte Carlo study of pairing instabilities on the honeycomb lattice Tao Ying, Stefan Wessel Using finite-temperature determinantal quantum Monte Carlo calculations, we re-examine the pairing susceptibilities in the Hubbard model on the honeycomb lattice, for doping onto and away from the van Hove singularity (VHS). Explicitly, two electronic fillings, 3/8 and 0.2 are considered. Due to a serious sign problem at strong coupling strengths, we focus on the weak interaction region of the Hubbard model Hamiltonian. From analyzing the temperature dependence of various pairing susceptibilities, we find different dominant pairing channels at and away from the VHS: in the later case, singlet d+id-wave is the dominant pairing state, while at the VHS, triplet next-nearest-neighbor f-wave pairing emerges as a leading instability. Possible instabilities to spin density wave states (SDW) are also investigated. [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:03PM |
B20.00009: Chernful excitations in two-dimensional quantum magnets Judit Romhanyi We discuss topological excitations in two-dimensional frustrated quantum spin models. In particular, we study systems in which the elementary magnetic building blocks are made of two or more spins $S=1/2$. The ground state in these models is formed by quantum mechanically entangled dimers and plaquettes, allowing for larger local Hilbert spaces and the emergence of multiplet excitations. We explain i) how perturbations to the models are able to open a gap in the bands of excited multiplet and ii) how relativistic spin-orbit coupling renders these bands topological in nature, resulting in unconventional Chern numbers. We will touch on possible experimental realization of these topological models. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B20.00010: Thermal phase transitions in the vicinity of the quantum critical point of spinless fermions on the honeycomb lattice Stephan Hesselmann, Stefan Wessel We consider spinless fermions on a honeycomb lattice (spinless $t-V$ model), which provide a minimal realization of lattice Dirac fermions. Nearest neighbor interactions drive a quantum phase transition from a semi-metallic phase to a charge ordered phase, which spontaneously breaks the chiral $Z_2$ symmetry of the Dirac fermions. The critical theory is given by the Gross-Neveu-Yukawa theory, which describes the process of mass generation due to the broken chiral symmetry. At finite temperature, and if $V>V_c$, the quantum critical point connects to a line of second order thermal phase transitions that restore the broken chiral symmetry. We employ recent sign-problem-free continuous time quantum Monte Carlo methods to investigate the finite temperature phase diagram of the model. Furthermore we give estimates for the critical exponents of the Gross-Neveu chiral Ising universality class by studying the extension of the quantum critical regime to finite temperatures. [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B20.00011: Signatures of fractionalization from inter-layer transport Shubhayu Chatterjee, Siddhardh Morampudi, Yochai Werman, Erez Berg Quantum spin liquids are unconventional insulating phases beyond the symmetry breaking paradigm with the prominent presence of fractionalized excitations. Due to the lack of distinguishing local order parameters, experimental signatures of such states are highly sought after. Many candidate materials for spin liquid states are layered quasi-2d materials, where each 2d layer is believed to have deconfined fractionalized excitations. We show that a signature of such excitations can be found by looking at the characteristics of in-layer versus inter-layer thermal transport in these materials, where distinct features arise reflecting the fact that the excitations are fractionalized. We also discuss how various forms of disorder influence the thermal conductivity. [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B20.00012: Topological edge states in correlated honeycomb materials with strong spin-orbit coupling Andrei Catuneanu, Heung-Sik Kim, Oguzhan Can, Hae-Young Kee We study the topological nature of single layers of correlated honeycomb materials $\alpha$-RuCl$_3$ and A$_2$IrO$_3$ (A=Li, Na) with strong spin-orbit coupling. An effective tight-binding model based on first principles band structure calculations including Hubbard interaction and spin-orbit coupling is derived. Two pairs of propagating edge modes centered at the zone center and zone boundary are found when their one-dimensional boundary forms a zig-zag shape, while the bulk has a gap with trivial time-reversal Z$_2$ invariants. The effects of strong electronic interactions and doping on the edge modes in these Mott insulators are discussed. We further suggest a heterostructure of $\alpha$-RuCl$_3$/IrCl$_3$ to search for the proposed topological Mott phase. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B20.00013: Kekule quantum criticality from Dirac fermion fluctuations: a functional RG approach Laura Classen, Michael Scherer, Igor Herbut We consider a system of Dirac fermions coupled to a Z3 order parameter field as it occurs in the Kekule valence bond solid on the honeycomb lattice. From Landau-Ginzburg paradigm, a discontinuous nature of the corresponding phase transition is expected due to the possibility of cubic terms in the free energy. This, however, has been challenged by scaling corrections due to fermionic quantum fluctuations (arXiv:1609.03208, arXiv:1610.07603). We study the modifications of scaling and the fixed point structure of a Gross-Neveu-Yukawa theory for this system employing the non-perturbative functional renormalization group. This enables a direct evaluation of critical behavior in 2+1 dimensions for an arbitrary number of fermions and provides access to non-perturbative information of the scalar effective potential. [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B20.00014: Effective Field Theory of Clean Interacting Semimetals G.J. De Coster, D. Belitz, T.R. Kirkpatrick We present an effective field theory for interacting electrons in clean semimetals (both Weyl semimetals and graphene) in terms of their soft or massless degrees of freedom. We show, by means of a Ward identity, that the intrinsic semimetal groundstate breaks an Sp$(N)$ symmetry of the theory. In Fermi liquids this enables one to identify the massive, non-Goldstone modes of the theory and integrate them out. Due to the vanishing density of states in semimetals, unlike in Fermi liquids, both Goldstone and non-Goldstone modes are equally soft, and so all two-particle correlations need to be kept. The resulting theory is not perturbative with respect to the electron-electron interaction; rather, it is controlled by means of a systematic loop expansion and allows for a renormalization-group analysis in a natural way. As a representative application, we use the theory to compute the zero-bias anomaly for the density of states for both short and long-range interactions in $d=2,3$. We find that the leading nonanalyticity in semimetals with a long-ranged interaction is identical to the one in Fermi liquids, since the effects of the vanishing density of states at the Fermi level are offset by the breakdown of screening. [Preview Abstract] |
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