Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D22: Theory of Exotic States of Matter 
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Sponsoring Units: DCMP Chair: EunAh Kim, Cornell University Room: 202A 
Monday, March 2, 2015 2:30PM  2:42PM 
D22.00001: Algebraic spin liquids with emergent generalized gauge boson excitations Alex Rasmussen, Cenke Xu, Zhen Bi, YiZhuang You According to an early proposal by Hermele, et.al., (condmat/0404751), an algebraic spin liquid state with gapless emergent photon excitations can exist in quantum spin ice systems. This algebraic spin liquid is stable against any weak perturbation. Futher work by Xu and Ho?ava (arxiv:1003.0009) concluded that certain lattice models give rise to more exotic stable spin liquid states with gravitonlike excitations. In this talk we will show how these algebraic spin liquid states can be generalized to even more exotic types of gapless excitations and then demonstrate that these new phases are stable against weak perturbations. [Preview Abstract] 
Monday, March 2, 2015 2:42PM  2:54PM 
D22.00002: (Almost) naked quantum criticality with nonFermi liquid behavior at the onset of inhomogeneous LarkinOvchinikov superfluidity in two dimensions Philipp Strack, Francesco Piazza We present a renormalization group analysis for the nonFermi liquid behavior and quantum criticality arising in coupled quantum wires of attractively interacting fermions with spin imbalance in two spatial dimensions. [Preview Abstract] 
Monday, March 2, 2015 2:54PM  3:06PM 
D22.00003: Topological Phases of Interacting Bosons on the Kagome Lattice Krishanu Roychowdhury, Subhro Bhattacharjee, Frank Pollmann We consider an extended Hubbard model of hard core bosons including nearestneighbour hopping and long range repulsive interactions on a kagome lattice. The system is an insulator at commensurate fillings of 1/6, 1/3 and 1/2 and can be mapped to different dimer models on the triangular lattice (depending on the filling). We focus on the filling of 1/3, which transforms to a fully packed loop (FPL) model, and derive the full phase diagram in the lowenergy subspace. Similar to the quantum dimer model and easyaxis kagome antiferromagnetic model studied before, we find an extended region of a gapped ${Z}_2$ liquid with vison excitations. The gauge fluctuations, responsible for the vison modes, are dictated by the action of an $\emph{even}$ Ising gauge theory. In the ordered phase, where the vison gap closes, we observe a 3fold rotationally symmetric loop ordering and present the critical theory for the amplitude fluctuations of the condensed modes. We also speculate the phase diagram for the fermionic counterpart of the model at all the above mentioned fractional fillings. [Preview Abstract] 
Monday, March 2, 2015 3:06PM  3:18PM 
D22.00004: Spontaneous Anomalous Hall states in metals Wathid Assawasunthonnet, Victor Chua, Eduardo Fradkin We explore two phases in 2D electron fluids with two Fermi surfaces in which the timereversal symmetry is broken spontaneously by using the method of higher dimensional bosonization. Earlier meanfield calculations [1] showed that the order parameter for both phases can be expressed as two twocomponent real vectors. There are two phases: the beta phase in which the two order parameters are perpendicular to each other and the alpha phase in which they are parallel. The beta phase exhibits nonvanishing unquantized spontaneous anomalous Hall effect at zero external magnetic fields, which is determined by a Berry curvature associated with Fermi surfaces. The alpha phase does not have that property. To go beyond meanfield, we use higher dimensional bosonization. We have identified the two phases in terms of classical approximations to the bosonized theory, which yields a state with broken timereversal invariance. We also find that the quantum phase transition from the timereversal invariant Fermi liquid state proceeds through a Pomeranchuktype instability. We will present results for the current and density correlations and collective modes in each phase. We will also discuss the possible connections between these states and exotic magnetic orders in metallic systems. [1] Kai Sun and Eduardo Fradkin, Phys. Rev. B 78, 245122 (2008). [Preview Abstract] 
Monday, March 2, 2015 3:18PM  3:30PM 
D22.00005: Transition of a $Z_3$ topologically ordered phase to a trivial phase ChingYu Huang, TzuChieh Wei Topologically ordered quantum systems have robust physical properties, such as quasiparticle statistics and groundstate degeneracy, which do not depend on the microscopic details of the Hamiltonian. We consider a topological phase transition under a string tension $g$ on a $Z_3$ topological state. This is first studied numerically in terms of the gaugesymmetry preserved quantum state renormalization group proposed by He, Moradi and Wen (arXiv:1401.5557). Modular matrices $S$ and $T$ can be obtained and used as order parameters to determine the critical string tension $g_c$. Then from a mapping to a classical 2D threestate Potts model on square lattice we obtain analytically the transition $g_c$ via the transition temperature of the threestate Potts model. We find the numerically determined $g_c$ agrees well with the analytic result via the mapping. [Preview Abstract] 
Monday, March 2, 2015 3:30PM  3:42PM 
D22.00006: Pairing instabilities of a NonFermi liquid in the presence of nematic and gauge fluctuations Andrej Mesaros, Michael J. Lawler, EunAh Kim In the absence of Fermiliquid starting point, instabilities of nonFermi liquids are theoretically challenging problems. Here we note that a nonFermi liquid state occurring at $\nu=1/2$ may be a promising concrete case for theoretical investigation of the issue for two reasons. Firstly, exotic ordered states observed in halffilled Landau levels, namely the FQH state at $\nu=5/2$ which is most likely best described as a paired state, and the quantum Hall nematic state at $\nu=9/2$, present a compelling possibility that the nonFermi liquid state with gauge fluctuations at $\nu=1/2$ is close to instabilities towards these ordered states. Secondly, a recent theoretical progress [Metlitski et al., arXiv:1403.3694] offers a scheme for a controlled renormalization group study of the problem. We will discuss competition between the two fluctuations in promoting or suppressing a superconducting instability, based on the phase diagram we obtain from a renormalization group calculation. [Preview Abstract] 
Monday, March 2, 2015 3:42PM  3:54PM 
D22.00007: Symmetry and BulkEdge Correspondence in the Dimerized Spin1/2 Heisenberg Ladder with External Magnetic Field Toshikaze Kariyado, Yasuhiro Hatsugai The dimerized spin1/2 Heisenberg ladder is topologically characterized from the viewpoints of symmetry protection and bulkedge correspondence. Our focus is on the plateau phase at the half of the saturation induced by dimerization and magnetic field. The Berry phase associated with the twisted boundary condition is employed as a topological order parameter. The magnetic field reduces the symmetry of the system, but there is a topological phase protected by a spatial inversion symmetry that is characterized by a Berry phase quantized to 0/$\pi$. For a Berry phase quantization, usage of a symmetrypreserving boundary, which leaves at least one inversion center after the system is cut at the boundary, is essential. As a comparison, a symmetrybreaking boundary is also analyzed. Naively, such a boundary is inadequate to make the Berry phase quantized and topological. However, for a specific type of boundary, we found a unique quantization of the Berry phase into $\pm \pi/2$, instead of 0/$\pi$ [T. Kariyado and Y. Hatsugai, Phys. Rev. B 90, 085132 (2014)]. Further, for the case of $\pm\pi/2$quantization, there appears an edge state distinct from the one for the 0/$\pi$quantization, which reveals new aspects of the bulkedge correspondence for symmetrybreaking boundary. [Preview Abstract] 
Monday, March 2, 2015 3:54PM  4:06PM 
D22.00008: Josephsoncoupled MooreRead states Layla Hormozi, Gunnar Moller, Joost Slingerland, Steven Simon We study a quantum Hall bilayer system of bosons at total filling fraction $\nu$ = 1, and analyze the the coupled MooreRead state [PRL 108, 256809 (2012)] that results from the interplay between shortranged interactions and interlayer pairtunneling terms. Supported by the exact solution of the full zeroenergy quasihole spectrum and a conformal field theory analysis, we develop an intuitive picture of this system as two coupled composite fermion superconductors. In this language, pair tunneling plays the role of Josephson coupling between the superconducting phases of the two layers, which gaps out the Goldstone mode associated with interlayer particle distribution. This coupling further implies that nonAbelian quasiparticles are confined between the layers. In the bulk, the resulting phase has the topological order of the Halperin 220 state i.e. U(1)$_2$ x U(1)$_2$ but the edge spectrum at a fixed particle number reveals an unexpected U(1)$_4$ x U(1) structure. We attribute this behavior to the fact that this state is realized in a rotated basis of layer index, where the charged and neutral sectors are separated. With the charge quantum number being conserved but without any such restriction on the neutral sector we show that the edge spectrum must take the observed form. [Preview Abstract] 

D22.00009: ABSTRACT WITHDRAWN 
Monday, March 2, 2015 4:18PM  4:30PM 
D22.00010: Ground State Degeneracy of Topological Phases on Open Surfaces Yidun Wan, Janet Hung we relate the ground state degeneracy (GSD) of a nonAbelian topological phase on a surface with boundaries to the anyon condensates that break the topological phase to a trivial phase. Specifically, we propose that gapped boundary conditions of the surface are in onetoone correspondence to the sets of condensates, each being able to completely break the phase, and we substantiate this by examples. The GSD resulting from a particular boundary condition coincides with the number of confined topological sectors due to the corresponding condensation. These lead to a generalization of the LaughlinWuTao chargepumping argument for Abelian fractional quantum Hall states to encompass nonAbelian topological phases, in the sense that an anyon loop of a confined anyon winding a nontrivial cycle can pump a condensate from one boundary to another. Such generalized pumping may find applications in quantum control of anyons, eventually realizing topological quantum computation. [Preview Abstract] 
Monday, March 2, 2015 4:30PM  4:42PM 
D22.00011: Parent Hamiltonians for Bosonic SymmetryProtected States Luiz Santos A platform for constructing parent Hamiltonians describing bosonic symmetryprotected (SPT) states will be presented. The Hamiltonians we consider are examples of frustrationfree RokhsarKivelson models, which are known to be in onetoone correspondence with classical stochastic systems in the same spatial dimensionality. By exploring this classicalquantum mapping we are able to propose Hamiltonians which, in a closed manifold, yield a unique gapped symmetric ground state describing the universal properties of SPT states. Specific examples which illustrate our approach shall be discussed. [Preview Abstract] 
Monday, March 2, 2015 4:42PM  4:54PM 
D22.00012: Quasionedimensional superfluid criticality PierreFrancois Duc, Michel Savard, Matei Petrescu, Adrian Del Maestro, Guillaume Gervais In one of the most celebrated examples of the theory of universal critical phenomena, superfluid $^{4}$He state belongs to the same three dimensional $\mathrm{O}(2)$ universality class as the onset of ferromagnetism in a lattice of $XY$ spins. Its ability to flow without viscosity below the $\lambda$transition temperature is a paradigmatic manifestation of emergent phenomena and macroscopic quantum coherence, driven by both strong interactions and bosonic quantum statistics. As the number of spatial dimensions decreases, it is expected that enhanced thermal and quantum fluctuations should push $T_\lambda\to 0$. However, in the one dimensional limit, the universal quantum hydrodynamics of Luttinger liquid theory should apply, providing a host of theoretical predictions including the simultaneous algebraic spatial decay of both densitydensity and superfluid correlation functions. At McGill University, we have designed an experiment and measured the DC mass flow of superfluid helium in {\it single} nanopores with radii down to 3 nm. For the smaller aperture, in which helium is expected to be in a `quasionedimensional' regime, the universal critical exponent for the superfluid velocity is found to deviate significantly from its bulk value, $\nu=\frac{2}{3}$. [Preview Abstract] 
Monday, March 2, 2015 4:54PM  5:06PM 
D22.00013: Electronic properties in a superlattice of strongly correlated electron systems Suguru Ueda, Norio Kawakami We theoretically investigate the superlattice consisting of a Mott insulator and a metal by using the dynamical meanfield theory. At low temperature, the quasiparticle state appears in the density of states of the Mott insulator layers. We address how the structure of the superlattice affects the stability of this Fermi liquid state. It is elucidated that the quasiparticle weight shows the characteristic evenodd oscillation depending on the thickness of the metal domain. We confirm this evenodd dependence in the electrical resistivity, and find that the Fermi liquid state is further stabilized by the superlattice with a certain periodicity. We also discuss the importance of our findings comparing with the recent experiments. [Preview Abstract] 
Monday, March 2, 2015 5:06PM  5:18PM 
D22.00014: The theory of cluster Mott insulator: charge fluctuation and spin liquids Gang Chen, HaeYoung Kee, Yong Baek Kim I will present recent theoretical work on cluster Mott insulators (CMI) in which interesting physics such as emergent charge lattices, charge fractionalization and quantum spin liquids are proposed. For the anisotropic Kagome system like LiZn2Mo3O8, we find two distinct CMIs, typeI and typeII, can arise from the repulsive interactions. In typeI CMI, the electrons are localized in one half of the triangle clusters of the Kagome system while the electrons in the typeII CMI are localized in every triangle cluster. Both CMIs are U(1) quantum spin liquids (QSL) in the weak Mott regime with a spinon Fermi surface and gapped charge excitations. In typeII CMI, however, the charge fluctuations lead to a longrange plaquette charge order that breaks the lattice symmetry, gives rise to an emergent charge lattice and reconstructs the meanfield spinon band structure of the underlying U(1) QSL. Such a reconstruction gives a consistent prediction of the ``fractional spin susceptibility'' that is observed in LiZn2Mo3O8. For the pyrochlore system, the CMI can further support a charge fractionalization with an emergent gauge photon in the charge sector in addition to the spin fractionalization in the spin sector. Experimental connection with the several cluster magnets such as LiZn2Mo3O8. [Preview Abstract] 
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