Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session Y44: Quantum Phase Transitions |
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Sponsoring Units: DCMP Chair: Dietrich Belitz, Univ of Oregon Room: LACC 504 |
Friday, March 9, 2018 11:15AM - 11:27AM |
Y44.00001: One-particle density matrix occupation spectrum of many-body localized states after a global quench Jens Bardarson , Talía Lezama , Soumya Bera , Henning Schomerus , Fabian Heidrich-Meisner The emergent integrability of the many-body localized phase is naturally understood in terms of localized quasiparticles. As a result, the occupations of the one-particle density matrix in eigenstates show a Fermi-liquid-like discontinuity. Here, we show that in the steady state reached at long times after a global quench from a perfect density-wave state, this occupation discontinuity is absent, reminiscent of a Fermi liquid at a finite temperature, while the full occupation function remains strongly nonthermal. We discuss how one can understand this as a consequence of the local structure of the density-wave state and the resulting partial occupation of quasiparticles. This partial occupation can be controlled by tuning the initial state and can be described by an effective temperature. |
Friday, March 9, 2018 11:27AM - 11:39AM |
Y44.00002: Metal-insulator crossover in FeSb2 within LQSGW+DMFT Sangkook Choi , Walber Brito , Patrick Semon , Gabriel Kotliar Although the thermoelectric properties of FeSb$_2$ are attracting attention due to its colossal thermopower and record-high thermoelectric power factor, the diamagnetic insulator-paramagnetic metal crossover does not fit within one-particle picture and are the subject of active research. Several theoretical models have been proposed to go beyond one-particle picture. However unified theory incorporating local and non-local electronic correlation and hybridization between the correlated and itinerant bands on the same footing is still missing. In this talk, we will discuss the effect of the electronic correlation and the hybridization to the crossover in FeSb$_2$. By using fully \textit{first-principles} approaches of LQSGW+DMFT without any adjustable parameters, we will show temperature evolution of spectral function, optical conductivity and local spin- and charge-fluctuation and make a comparison with experiments. |
Friday, March 9, 2018 11:39AM - 11:51AM |
Y44.00003: Evidence of the melting of Wigner crystals Talbot Knighton , Alessandro Serafin , zhe Wu , Jiansheng Xia , Jian Huang , Loren Pfeiffer , K West Electron systems governed by Coulomb interaction manifest remarkable correlated phenomena among which a Wigner crystal (WC) has been a long-sought-after example. Because a WC is sustained by dominating Coulomb interaction, experimental observations require systems with ultra-low carrier densities (down to 10^{9}cm^{-2} or r_{s} ∼40), a limit where interaction effect at such tiny energy scales is easily overwhelmed by disorder. As a result, a WC has not been previously demonstrated. Most detections made by transport and resonance techniques found only softly pinned modes that undergo second-order-like melting transition. Because the corresponding translational correlation length ξ is small, they are reasonably explained as intermediate/mixed phases.(i.e. hexatic and glass phases). Utilizing ultra-pure 2D systems, this study demonstrates for the first time nonlinear dc-IV results in r_{s}>40 limit at T down to 10 mK. Enormous pinning characterized by GΩ resistance found below a critical temperature of T_{c}~30mK supports a WC on almost a macroscopic scale of ξ. The thermal melting follows a two-stage process resembling the Kosterlitz-Thouless model, except that a striking discontinuity appearing in the differential resistance at T_{c }suggests a first-order transition. |
Friday, March 9, 2018 11:51AM - 12:03PM |
Y44.00004: Competing phases and orbital-selective behaviors in the two-orbital Hubbard-Holstein model Shaozhi Li , Ehsan Khatami , Steven Johnston In recent years, electron-electron (e-e) interactions in multiorbital Hubbard models have been widely studied. However, surprisingly little is known about how multiorbital phenomena like the orbital-selective Mott phase (OSMP) are affected by the electron-phonon (e-ph) interaction. In this talk, we present a study of the interplay between e-e and e-ph interactions in the degenerate two-orbital Hubbard-Holstein model at half filling using the dynamical mean-field theory. We find that the e-ph interaction, even at weak couplings, strongly modifies the underlying phase diagram of this model, reshaping the orbital-selective behavior and introducing a new orbital-selective phase, the orbital-selective Peierls phase (OSPI). Specifically, at small e-e and e-ph couplings, we find a competition between the OSMP and the OSPI, while at large couplings, a competition occurs between the Mott and charge-density-wave (CDW) phases. We further demonstrate that the Hund’s coupling favors the OSPI transition by lowering the energy associated with the CDW. Our results are important since many researchers have dismissed the relevance of the e-ph interaction in the iron-based superconductors due to an early predictions of weak e-ph interaction strengths. [Phys. Rev. B 95, 121112(R) (2017)] |
Friday, March 9, 2018 12:03PM - 12:15PM |
Y44.00005: Quantum Phase Transitions of the Majorana Toric Code in the Presence of Finite Cooper-pair Tunneling Ananda Roy , Barbara Terhal , Fabian Hassler The toric code based on Majorana fermions on mesoscopic superconducting islands is a promising candidate for quantum information processing. In the limit of vanishing Cooper-pair tunneling, it has been argued that the phase transition separating the topologically-ordered, toric code phase from the trivial one is in the universality class of (2+1)D-XY. On the other hand, in the limit of infinitely large Cooper-pair tunneling, the phase transition is in the universality class of (2+1)D-Ising. In this work, we treat the case of finite Cooper-pair tunneling and address the question of how the continuous XY symmetry breaking phase transition turns into a discrete Z_{2} symmetry breaking one when the Cooper-pair tunneling rate is increased. We show that this happens through a couple of tricritical points and first order phase transitions. Using a Jordan-Wigner transformation, we map the problem to that of spins coupled to quantum rotors. Then, we propose a Landau field theory for this model that matches the known results in the respective limits. Our results are relevant for predicting the stability of the topological phase in realistic experimental implementations. |
Friday, March 9, 2018 12:15PM - 12:27PM |
Y44.00006: Solvable Haldane Hubbard model at Falicov-Kimball limit with Topological Phase Transition Xiaohui Ll , Zewei Chen , Tai-Kai Ng In this talk, we present a spin dependent Haldane model with Hubbard onsite interaction. In the limit when the model is reduced to the exactly solvable Falicov-Kimball model (FKM) [1], we find an interaction driven topological phase transition and a solitonic excitation with bound particle in the topological trivial region. Deviated from FKM limit, we solve this model with a mean-field approach where the Chern number phase diagram with respect to interaction is obtained. Experimentally, this model can be realized in cold atom system with imbalanced left and right circular light[2]. More generally, we explore three classes of models that can be mapped to FKM at certain symmetric point. In strong interacting limit, we found these models can be described by some effective classical Ising models. |
Friday, March 9, 2018 12:27PM - 12:39PM |
Y44.00007: Emergent Spacetime Supersymmetry at the Superconducting Critical Point of a Single Dirac Cone Zixiang Li , Abolhassan Vaezi , Christian Mendl , Hong Yao It has been theoretically argued that SUSY can also spontaneously emerge in certain condensed matter systems, e.g., near the superconducting quantum critical point (QCP) of an interacting single-flavored Dirac fermion in 2+1 dimensional systems. However, whether this fascinating N=2 SUSY can emerge in microscopic lattice models in 2+1 dimensions remain unknown so far. Here, we introduce a lattice realization of a single Dirac fermion with onsite attractive Hubbard interactions that preserves both time reversal and chiral symmetries. By performing the state-of-the-art sign-problem-free quantum Monte Carlo (QMC) simulations, we show that the interacting single Dirac fermion in 2+1 dimensions features a superconducting quantum phase transition. More remarkably, we demonstrate that the N=2 space-time SUSY in 2+1D emerges at the superconducting QCP by showing that the fermions and bosons have identical anomalous dimensions 1/3 as well as various other hallmarks of emergent SUSY. To the best of our knowledge, this is the first numerical observation of emergent space-time SUSY in 2+1D systems [1]. |
Friday, March 9, 2018 12:39PM - 12:51PM |
Y44.00008: Thermalization of a Chiral Floquet Edge Dan Borgnia , Hoi Chun Po , Vedika Khemani , Ashvin Vishwanath Following the recent construction of chiral topological phases in 2D Floquet systems reliant on many-body localization (MBL) for stability, we examine the thermalization of a 1D MBL chiral edge. While the eigenstates of the 1D Floquet unitary are delocalized, the dynamics of thermalization separates into two regimes of entanglement entropy (EE) growth, linear and logarithmic. In the thermodynamic limit, thermalization occurs on a linear time scale and appears to depend on rare regions of the MBL Hamiltonian. We detail the mechanism by which edge thermalization occurs and probe this behavior via exact diagonalization for small system sizes over long time scales, and Time-evolving block decimation (TEBD) on a 1D MPS for larger system sizes at early times. |
Friday, March 9, 2018 12:51PM - 1:03PM |
Y44.00009: Dynamical Quantum Phase Transitions in Systems with Continuous Symmetry Breaking Simon Weidinger , Markus Heyl , Alessandro Silva , Michael Knap Interacting many-body systems that are driven far away from equilibrium can exhibit phase transitions between dynamically emerging quantum phases, which manifest as singularities in the Loschmidt echo. Whether and under which conditions such dynamical transitions occur in higher-dimensional systems with spontaneously broken continuous symmetries is largely elusive thus far. Here, we study the dynamics of the Loschmidt echo in the three dimensional O(N) model following a quantum quench from a symmetry breaking initial state. The O(N) model exhibits a dynamical transition in the asymptotic steady state, separating two phases with a finite and vanishing order parameter, that is associated with the broken symmetry. We analytically calculate the rate function of the Loschmidt echo and find that it exhibits periodic kink singularities when this dynamical steady-state transition is crossed. The singularities arise exactly at the zero-crossings of the oscillating order parameter. As a consequence, the appearance of the kink singularities in the transient dynamics is directly linked to a dynamical transition in the order parameter. Furthermore, we argue, that our results for DQPTs in the O(N) model are general and apply to generic systems with continuous symmetry breaking. |
Friday, March 9, 2018 1:03PM - 1:15PM |
Y44.00010: Self-Learning Monte Carlo study of Holstein Model Chuang Chen , Xiao Yan Xu , Junwei Liu , Richard Scalettar , George Batrouni , ZiYang Meng We design a self-learning Monte Carlo algorithm for the study of Holstein model at half filling, which is notorious for its slow Monte Carlo dynamics in a wide temperature range across the charge-density-wave phase transition. Self-learning Monte Carlo method extracts an effective bosonic Hamiltonian that captures the low-energy physics of the problem originated from the coupling between electrons and phonons. The update of the effective Hamiltonian is more efficient and greatly reduces the auto-correlation among the phonon configurations. Because of its considerable speedup over traditional Determinant quantum Monte Carlo method, we are able to simulate Holstein model with much larger system sizes and study the scaling behaviors near the critical point and acquire the critical exponents with high accuracy. |
Friday, March 9, 2018 1:15PM - 1:27PM |
Y44.00011: Detecting non-equilibrium quantum phase transitions by violations of Leggett-Garg inequalities Fernando Gómez-Ruiz , Juan Mendoza-Arenas , Ferney Rodriguez , Luis Quiroga Non-equilibrium quantum phase transitions in correlated systems have been the object of recent intense research, and new characterization methods are valuable for their analysis. In this work, we discuss how single-site two-time correlation (STC) and Leggett-Garg inequalities (LGIs) identify the critical points of such transitions. We exemplify this on a testbed out-equilibrium configuration, namely a one-dimensional spin-1/2 lattice connected to Markovian reservoirs of different magnetization at its boundaries. When described by an XXZ Hamiltonian, the steady state features a transition from ballistic to diffusive spin transport at the isotropic point. By performing large-scale matrix product simulations we obtain STC for dichotomic operators, and demonstrate that the transition is determined by a change of direction of the maximal violation of LGIs. In addition we show that LGIs are sensible to transport changes induced by dephasing. In particular we find that for strong interactions and large driving, where dephasing leads to an insulating-diffusive transition, a large increase of their violations occurs. This corresponds to a new observation of quantum behavior enhancement by decoherence. |
Friday, March 9, 2018 1:27PM - 1:39PM |
Y44.00012: Gauge field fluctuations and Weiss oscillations about the half-filled Landau level Amartya Mitra , Michael Mulligan Numerical [Phys. Rev. Lett. 84, 4685 (2000)], [Science 352, 6282 (2016)] and experimental [Phys. Rev. Lett. 113, 196801 (2014)] observations indicate that a particle-hole (PH) symmetry is realized by two-dimensional electrons that half-fill a Landau level. Prior work [Phys. Rev. B 95,23 (2017)] studied the implications of weakly broken PH symmetry on Weiss oscillations, a type of magnetoresistance oscillation, about half-filling using the Dirac composite fermion theory proposed by Son [Phys. Rev. X 5, 031027 (2015)]. Here, we extend this prior work by including the effects of fluctuations of the emergent gauge field that couples to the Dirac composite fermion. We compare our results to experiment and other composite fermions theories such as [Phys. Rev. B 47, 7312 (1993)] and [Phys. Rev. B 92,16 (2015)]. |
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