87,637 research outputs found
Personal Papers (MS 80-0002)
No full textLetter from F. L. Meisner to Daniel W. Kempner discussing a broken clock
Quantum phases of strongly interacting bosons on a two-leg Haldane ladder
No full textWe study the ground-state physics of a single-component Haldane model on a hexagonal two-leg ladder geometry with a particular focus on strongly interacting bosonic particles. We concentrate our analysis on the regime of less than one particle per unit cell. As a main result, we observe several Meissner-like and vortex-fluid phases, both for a superfluid as well as a Mott-insulating background. Furthermore, we show that for strongly interacting bosonic particles, an unconventional vortex-lattice phase emerges, which is stable even in the regime of hard-core bosons. We discuss the mechanism for its stabilization for finite interactions by a means of an analytical approximation. We show how the different phases may be discerned by measuring the nearest- and next-nearest-neighbor chiral currents as well as their characteristic momentum distributions
Transport in quasi one-dimensional spin-1/2 systems
No full textWe present numerical results for the spin and thermal conductivity of
one-dimensional (1D) quantum spin systems. We contrast the properties of
integrable models such as the spin-1/2 XXZ chain against nonintegrable ones such as
frustrated and dimerized chains. The thermal conductivity of the XXZ chain
is ballistic at finite temperatures, while in the nonintegrable models, this quantity is argued
to vanish. For the case of frustrated and dimerized chains, we discuss
the
frequency dependence of the transport coefficients. Finally, we give an overview over related theoretical
work on intrinsic and extrinsic scattering mechanisms of quasi-1D spin systems
Temporal decay of Néel order in the one-dimensional Fermi-Hubbard model
No full textMotivated by recent experiments with ultracold quantum gases in optical lattices we study the decay of the staggered moment in the one-dimensional Fermi-Hubbard model starting from a perfect Néel state using exact diagonalization and the infinite-system-size time-evolving-block-decimation method. This extends previous work in which the same problem has been addressed for pure spin Hamiltonians. As a main result, we show that the relaxation dynamics of the double occupancy and of the staggered moment are different. The former is controlled by the nearest-neighbor tunneling rate while the latter is much slower and strongly dependent on the interaction strength, indicating that spin excitations are important. This difference in characteristic energy scales for the fast charge dynamics and the much slower spin dynamics is also reflected in the real-time evolution of nearest-neighbor density and spin correlations. A very interesting time dependence emerges in the von Neumann entropy, which at short times increases linearly with a slope proportional to the tunneling matrix element while the long-time growth of entanglement is controlled by spin excitations. Our predictions for the different relaxation dynamics of the staggered moment and the double occupancy should be observable in state-of-the-art optical lattice experiments. We further compare time averages of the double occupancy to the expectation values in both the canonical and diagonal ensembles, which quantitatively disagree with each other on finite systems. We relate the question of thermalization to the eigenstate thermalization hypothesis
Scaling properties of a spatial one-particle density-matrix entropy in many-body localized systems
No full textWe investigate a spatial subsystem entropy extracted from the one-particle density matrix (OPDM) of one-dimensional disordered interacting fermions that host a many-body localized (MBL) phase. Deep in the putative MBL regime, this OPDM entropy exhibits the salient scaling features of localization, even though it provides only an upper bound to the von Neumann entropy. First, we numerically show that the OPDM entropy of the eigenstates obeys an area law. Second, like the von Neumann entropy, the OPDM entropy grows logarithmically with time after a quantum quench, albeit with a different prefactor. Both these features survive at moderately large interactions and well toward the transition into the ergodic phase. We discuss prospects for calculating the OPDM entropy using approximate numerical methods and for its measurement in quantum gas experiments
Transport in dimerized and frustrated spin systems
No full textWe analyze the Drude weight for both spin and thermal transport of one-dimensional spin-12 systems by means of exact diagonalization at finite temperatures. While the Drude weights are non-zero for finite systems, we find indications of a vanishing of the Drude weights in the thermodynamic limit for non-integrable models implying normal transport behavior.Fil: Heidrich Meisner, F.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; AlemaniaFil: Honecker, A.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; AlemaniaFil: Cabra, Daniel Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Ecole Normale Supérieure de Lyon; FranciaFil: Brenig, W.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; Alemani
Comment on “Anomalous Thermal Conductivity of Frustrated Heisenberg Spin Chains and Ladders
No full textA Comment on the Letter by J.V. Alvarez and Claudius Gros, Phys. Rev. Lett. 89, 156603 (2002). The authors of the Letter offer a Reply. © 2004 The American Physical Society.Fil: Heidrich-Meisner, F.. Institut für Theoretische Physik; AlemaniaFil: Honecker, A.. Institut für Theoretische Physik; AlemaniaFil: Cabra, Daniel Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Centre National de la Recherche Scientifique. Laboratoire de Physique Et Chimie de I´environnement Et de I´espace; FranciaFil: Brenig, W.. Institut für Theoretische Physik; Alemani
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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