Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session Y27: Low Dimensional Correlated Systems |
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Sponsoring Units: DCMP Chair: Ben Ueland, Ames National Laboratory Room: 326 |
Friday, March 18, 2016 11:15AM - 11:27AM |
Y27.00001: Electromagnetic response of time-reversal breaking metallic phases in two dimensions Victor Chua, Wathid Assawasunthonnet, Eduardo Fradkin The electromagnetic response of models of nematic non Fermi-liquids previously proposed in Ref.[1] are re-examined using conventional many-body methods. Nematic phases of this model are described by two 2-component real vectors which express the isotropy breaking nematicity in two Fermi-surfaces. Of interest is the time-reversal symmetry breaking nematic phase with a non-vanishing unquantized spontaneous anomalous Hall effect at zero external magnetic fields, and has a geometrical description as a Berry phase. We compare and contrast our results with conventional response calculations with those predicted with the higher-dimensional bosonization method [2,3]. Finally we present preliminary results on an RG analysis of this system. [1] K Sun and E Fradkin, Phys. Rev. B 78, 245122 (2008). [2] HJ Kwon, A Houghton, and JB Marston, Phys. Rev. B 52, 8002 (1995) [3] MJ Lawler, DG Barci, V Fernández, E Fradkin, L Oxman, Phys. Rev. B 73, 085101 (2006) [Preview Abstract] |
Friday, March 18, 2016 11:27AM - 11:39AM |
Y27.00002: Transport in a One-Dimensional Hyperconductor Eugeniu Plamadeala, Michael Mulligan, Chetan Nayak We define a `hyperconductor' to be a material whose electrical and thermal DC conductivities are infinite at zero temperature. The low-temperature behavior of a hyperconductor is controlled by a quantum critical phase of interacting electrons that is stable to all potentially-gap-generating interactions and arbitrary potentially-localizing disorder. We compute the low-temperature DC and AC electrical and thermal conductivities in a one-dimensional hyperconductor, studied previously by the present authors, in the presence of both disorder and umklapp scattering. We identify the conditions under which the transport coefficients are finite, and exhibit examples of violations of the Wiedemann-Franz law. We show that the temperature dependence of the electrical conductivity is a power law, $\sigma \propto 1/T^{1 - 2(2-\Delta_X)}$ for $\Delta_X \geq 2$, down to zero temperature when the Fermi surface is commensurate with the lattice. In the incommensurate case with weak disorder, such scaling is seen at high-temperatures, followed by an exponential increase of the conductivity $\ln \sigma \sim 1/T$ at intermediate temperatures and, finally, $\sigma \propto 1/T^{2-2(2-{\Delta_X})}$ at the lowest temperatures. In both cases, the thermal conductivity diverges at low temperatures. [Preview Abstract] |
Friday, March 18, 2016 11:39AM - 11:51AM |
Y27.00003: Photon-dressed quasiparticle states in 1D and 2D materials: a many-body Floquet approach Franca Manghi, Matteo Puviani We studiy the interplay between electron-electron interactions and non-equilibrium conditions associated to time-dependent external fields. Exploring phases of quantum matter away from equilibrium may give access to regimes inaccessible under equilibrium conditions. What makes this field particularly interesting is the possibility to engineer new phases of matter by an external tunable control. We have developed a scheme that allows to treat photo-induced phenomena in the presence of electron-electron many body interactions, where both the nonlinear effects of the external field and the electron-electron correlation are treated simultaneously and in a non-perturbative way. The Floquet approach is used to include the effects of the external time periodic field, and the Cluster Perturbation Theory to describe interacting electrons in a lattice. They are merged in a Floquet-Green function method that allows to calculate photon dressed quasiparticle excitation. For 1D systems we show that an unconventional Mott insulator-to-metal transition occurs for given characteristics of the applied field (intensity and frequency). The method has also been applied to the 2D honeycomb lattice (graphene), where in the presence of realistic values of electron-electron interaction, we show that linearly polarized light may give rise to non-dissipative edge states associated to a non-trivial topological behavior. [Preview Abstract] |
Friday, March 18, 2016 11:51AM - 12:03PM |
Y27.00004: Composite fermions and the field-tuned superconductor-insulator transition Srinivas Raghu, Michael Mulligan In several two-dimensional films that exhibit a magnetic field-tuned superconductor to insulator transition (SIT), stable metallic phases have been observed. Building on the `dirty boson' description of the SIT, we suggest that the metallic region is analogous to the composite Fermi liquid observed about half-filled Landau levels of the two-dimensional electron gas. The composite fermions here are mobile vortices attached to one flux quantum of an emergent gauge field. The composite vortex liquid is a 2D non-Fermi liquid metal, which we argue is stable to weak quenched disorder. We describe several experimental consequences of the emergent composite vortex liquid. [Preview Abstract] |
Friday, March 18, 2016 12:03PM - 12:15PM |
Y27.00005: Mirror symmetry and the half-filled Landau level Michael Mulligan, Shamit Kachru, Gonzalo Torroba, Huajia Wang We study the dynamics of the half-filled zeroth Landau level of Dirac fermions using mirror symmetry, a supersymmetric duality between certain pairs of 2 + 1-dimensional theories. We show that the half-filled zeroth Landau level of a pair of Dirac fermions is dual to a pair of Fermi surfaces of electrically-neutral composite fermions, coupled to an emergent gauge field. Thus, we use supersymmetry to provide a derivation of flux attachment and the emergent Fermi liquid-like state for the lowest Landau level of Dirac fermions. We find that in the dual theory the Coulomb interaction induces a dynamical exponent z = 2 for the emergent gauge field, making the interactions classically marginal. This enables us to map the problem of 2+1-dimensional Dirac fermions in a finite transverse magnetic field, interacting via a strong Coulomb interaction, into a perturbatively controlled model. We analyze the resulting low-energy theory using the renormalization group and determine the nature of the BCS interaction in the emergent composite Fermi liquid. [Preview Abstract] |
Friday, March 18, 2016 12:15PM - 12:27PM |
Y27.00006: Phase transitions induced by magnetic field in graphite Benoit Fauque, David LeBoeuf, Willem Rischau, Wojciech Tabis, Baptiste Vignolle, Cyril Proust, Kamran Behnia Graphite is compensated semi-metals characterized by a tiny three dimensional Fermi surface. A magnetic field of about 10T is large enough to confine electrons and holes to their lowest Landau levels. These are therefore ideal candidates to explore the nature of the electronic ground state of a three-dimensional electron gas pushed beyond the so-called quantum limit. Various instabilities have been predicted in this peculiar limit where electronic interactions are enhanced. We find that the magnetic field induces two successive phase transitions, made of two distinct ordered states, each restricted to a finite field window. In both states, the in-plane and out-of plane conductivity behaves differently : not only the onset of the transition are different in both quantity but also an energy gap opens up in the out-of-plane conductivity and coexists with an unexpected in-plane metallicity for a fully gap bulk system. Such peculiar metallicity may arise as a consequence of edge-state transport expected to develop in the presence of a bulk gap. [Preview Abstract] |
Friday, March 18, 2016 12:27PM - 12:39PM |
Y27.00007: Exotic insulating states of $(t_{2g})^4$ Hubbard model with spin-orbit coupling Toshihiro Sato, Tomonori Shirakawa, Seiji Yunoki We numerically study electronic properties of a $t_{2g}$-orbital Hubbard model with a relativistic spin-orbit coupling (SOC) at four electrons per site. Our approach is a multi-orbital dynamical mean field theory with a continuous-time quantum Monte Carlo solver based on a strong coupling expansion. The main issue is the variation of electronic structure in the parameter space of the SOC and the Coulomb interactions at temperature fixed. For larger Coulomb interactions, a Van Vleck-type nonmagnetic insulating state with a total angular momentum $J=0$ is induced by the SOC. When the SOC decreases, the insulating state is magnetically ordered along with increasing the hybridization between a nonmagnetic $J=0$ state and an excited $J=1$ state. Moreover, for smaller Coulomb interactions, we demonstrate that an excitonic insulating state without magnetic order appears, in addition to metallic and band insulating states. The exciton condensation is formed by an electron-hole pairing between the local effective total angular momentum $j=1/2$ and $j=3/2$ based bands. [Preview Abstract] |
Friday, March 18, 2016 12:39PM - 12:51PM |
Y27.00008: Vison Condensation and Bond Density Wave Order in the Cuprates Aavishkar Patel, Andrea Allais, Debanjan Chowdhury, Subir Sachdev We consider Z2 spin liquids on the square lattice. These can undergo a confinement transition to a valence bond solid (VBS) phase via the condensation of vortex excitations carrying Z2 magnetic flux (visons) [1]. The resulting condensed phase is described by a fully frustrated Ising model (FFIM) on the dual square lattice, with additional couplings allowed by symmetries. We argue that such a model can also apply to confinement transitions out of the fractionalized Fermi liquid (FL*) states of doped antiferromagnets. We study the low energy states of such a model and discuss their implications for the incommensurate d-form factor bond density wave order observed in several recent experiments on the cuprate superconductors. [1] R. Jalabert and S. Sachdev, Phys. Rev. B 44, 686 (1991). [Preview Abstract] |
Friday, March 18, 2016 12:51PM - 1:03PM |
Y27.00009: Transition from the Z2 spin liquid to antiferromagnetic order: spectrum on the torus Seth Whitsitt, Subir Sachdev We study the finite-size spectrum of the quantum critical point between a $\mathbb{Z}_2$ spin liquid and a coplanar antiferromagnet on the torus. Due to the existence of nontrivial order on either side of this transition, this critical point cannot be described in a conventional Landau-Ginzburg framework. Instead it is described by a theory involving fractionalized degrees of freedom known as the $O(4)^*$ model, whose spectrum is altered in a significant way by its proximity to a topologically ordered phase. We compute the spectrum by relating it to the spectrum of the $O(4)$ Wilson-Fisher fixed point on the torus, along with a selection rule on the states, and with nontrivial boundary conditions corresponding to topological sectors in the spin liquid. The spectrum of the Wilson-Fisher fixed points is then calculated directly from the $\epsilon$- and large-$N$ expansions, which allows a reconstruction of the full spectrum of the $O(4)^*$ model. This spectrum is a unique characteristic of a fractionalized quantum critical point as well as a universal signature of the existence of a proximate $\mathbb{Z}_2$ topological phase which can be compared with numerical computations. [Preview Abstract] |
Friday, March 18, 2016 1:03PM - 1:15PM |
Y27.00010: Long-range Coulomb interaction in nodal ring semi-metals Yejin Huh, Eun-Gook Moon, Yong Baek Kim Recently there have been several proposals of materials predicted to be nodal ring semi-metals, where zero energy excitations are characterized by a nodal ring in the momentum space. This class of materials falls between the Dirac-like semi-metals and the more conventional Fermi-surface systems. As a step towards understanding this unconventional system, we explore the effects of the long-range Coulomb interaction. Due to the vanishing density of states at the Fermi level, Coulomb interaction is only partially screened and remains long-ranged. Through renormalization group and large-$N_f$ computations, we have identified a non-trivial interacting fixed point. The screened Coulomb interaction at the interacting fixed point is an irrelevant perturbation, allowing controlled perturbative evaluations of physical properties of quasiparticles. We discuss unique experimental consequences of such quasiparticles: acoustic wave propagation, anisotropic DC conductivity, and renormalized phonon dispersion as well as energy dependence of quasiparticle lifetime. [Preview Abstract] |
Friday, March 18, 2016 1:15PM - 1:27PM |
Y27.00011: Scaling of Greenwood Peierls conductance on a diluted square lattice William Schwalm, Albert Schmitz The modified rectangle lattice of Dhar is a bond-diluted square lattice. The structure is self-similar and finitely ramified, like a fractal. Nevertheless certain discrete Schr\"{o}dinger equation Green functions for the modified rectangle are known in closed form in the infinite lattice limit and the spectrum is continuous. By standard transfer matrix renormalization methods we present a study scaling properties of the Greenwood Peierls conductance distribution across the lattice with one dimensional lead wires attached as a function of lattice size and of additional disorder of several types. [Preview Abstract] |
Friday, March 18, 2016 1:27PM - 1:39PM |
Y27.00012: Phase coexistence in the O($N$)$\oplus$O($M$) nonlinear sigma model: a conformal bootstrap study Chris Hooley, Sam Ridgway The low-temperature physics of systems with competing orders is a ubiquitous topic in modern condensed matter physics. A commonly studied field theory of such systems is the O($N$)$\oplus$O($M$) nonlinear sigma model: an O($N+M$) model with a mass term attached to $N$ of the field components. Depending on the sign of the mass term, order in the O($N$) sector or the O($M$) sector is favored. However, the physics near the high-symmetry point is subtle, and in some cases (e.g. $N=M=2$) it remains unclear whether there is a first-order spin-flop transition or a finite-width microscopic coexistence phase. In this talk, we present an analysis of the O($N$)$\oplus$O($M$) model based on the conformal bootstrap method. This allows us to classify the critical points of the models in question, and by extension determine whether a coexistence phase exists or not. [Preview Abstract] |
Friday, March 18, 2016 1:39PM - 1:51PM |
Y27.00013: Quantum Monte Carlo study of hard-core bosons in a pyrochlore lattice with six-site ring-exchange interactions Catherine Tieman, Valery Rousseau Highly frustrated quantum systems on lattices can exhibit a wide variety of phases. In addition to the usual Mott insulating and superfluid phases, these systems can also produce some so-called ``exotic phases", such as super-solid and valence-bond-solid phases. An example of particularly frustrated lattice is the pyrochlore structure, which is formed by corner-sharing tetrahedrons. Many real materials adopt this structure, for instance the crystal $Cd_2Re_2O_7$, which exhibits superconducting properties. However, the complex structure of these materials combined with the complexity of the dominant interactions that describe them makes their analytical study difficult. Also, approximate methods, such as mean-field theory, fail to give a correct description of these systems. In this work, we report on the first exact quantum Monte Carlo study of a model of hard-core bosons in a pyrochlore lattice with six-site ring-exchange interactions, using the Stochastic Green Function (SGF) algorithm. We analyze the superfluid density and the structure factor as functions of the filling and ring-exchange interaction strength, and we map out the ground state phase diagram. [Preview Abstract] |
Friday, March 18, 2016 1:51PM - 2:03PM |
Y27.00014: Phase Diagram of the $Z_3$ Parafermionic Chain with Chiral Interactions Ye Zhuang, Hitesh Changlani, Norm Tubman, Taylor Hughes Majorana fermions and parafermions are exotic quasiparticles with non-Abelian fractional statistics that can be realized and stabilized in one-dimensional models. We study the simplest generalization of the Kitaev p-wave wire, i.e. the $Z_3$ parafermionic chain [Phys. Rev. B 92, 035154 (2014)]. Using a Jordan-Wigner transform we focus on the equivalent three-state chiral clock model, and study its rich phase diagram using the density matrix renormalization group technique. We perform our analyses using quantum entanglement diagnostics which allow us to determine phase boundaries, and the nature of the phase transitions. In particular, we study the transition between the topological (ordered) and trivial phases (disordered), as well as to an intervening critical (incommensurate) phase which appears in a wide region of the phase diagram. The phase diagram is predicted to contain a Lifshitz type transition which we confirm using entanglement measures. We also attempt to locate and characterize a putative tricritical point in the phase diagram where the three above mentioned phases meet at a single point. [Preview Abstract] |
Friday, March 18, 2016 2:03PM - 2:15PM |
Y27.00015: Photon-induced phase transitions of individual electronic phase separated domains in manganites strips Hanxuan Lin, Kai Zhang, Hao Liu, Tian Miao, Yang Yu, Lifeng Yin, Jian Shen Effective photosensors should be built on materials whose properties depend sensitively on light. Manganites are one of the candidates, where light can trigger resistivity change by several orders of magnitude. Such dramatic change is often associated with photoinduced phase transitions of electronic phase separated (EPS) domains in manganites. Previous studies of the light effect all use macroscopic manganite samples, which consist of large numbers of EPS domains smearing out the photon-induced phase transitions. Here, we observe the signature of individual domains' photoinduced phase transition by macroscopic transport measurement of spatially confined manganites strips. Pronounced photon-induced resistivity jumps emerge in the warming process, which reveals the dynamics of the phase transitions of individual EPS domains upon interaction with light. Magnetic force microscope (MFM) has been used to investigate the mechanism of those resistivity jumps. [Preview Abstract] |
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