Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y18: Invited Session: New Approaches to the Non-Equilibrium Quantum Many-Body Problem |
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Sponsoring Units: DCOMP Chair: Andrew Millis, Columbia University Room: Mission Room 103A |
Friday, March 6, 2015 8:00AM - 8:36AM |
Y18.00001: Bold-line Monte Carlo and the nonequilibrium physics of strongly correlated many-body systems Invited Speaker: Guy Cohen This talk summarizes real time bold-line diagrammatic Monte-Carlo approaches to quantum impurity models, which make significant headway against the sign problem by summing over corrections to self-consistent diagrammatic expansions rather than a bare diagrammatic series. When the bold-line method is combined with reduced dynamics techniques\footnote{Guy Cohen, Eli Y. Wilner, and Eran Rabani. New Journal of Physics 15, 073018 (2013).} both local single-time properties\footnote{Guy Cohen, Emanuel Gull, David R. Reichman, Andrew J. Millis, and Eran Rabani. Physical Review B 87, 195108 (2013).} and two time correlators such as Green functions\footnote{Guy Cohen, David R. Reichman, Andrew J. Millis, and Emanuel Gull. Physical Review B 89, 115139 (2014).} can be computed at very long timescales, enabling studies of nonequilibrium steady state behavior of quantum impurity models\footnote{Guy Cohen, Emanuel Gull, David R. Reichman, and Andrew J. Millis. Physical Review Letters 112, 146802 (2014).} and creating new solvers for nonequilibrium dynamical mean field theory. [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 9:12AM |
Y18.00002: The time-dependent Gutzwiller approximation Invited Speaker: Michele Fabrizio The time-dependent Gutzwiller Approximation (t-GA) [1,2] is shown to be capable of tracking the off-equilibrium evolution both of coherent quasiparticles and of incoherent Hubbard bands. The method is used to demonstrate that the sharp dynamical crossover observed by time-dependent DMFT in the quench-dynamics of a half-filled Hubbard model can be identified within the t-GA as a genuine dynamical transition separating two distinct physical phases [3]. This result, strictly variational for lattices of infinite coordination number, is intriguing as it actually questions the occurrence of thermalization. Next, we shall present how t-GA works in a multi-band model for V$_{2}$O$_{3}$ that displays a first-order Mott transition. We shall show that a physically accessible excitation pathway is able to collapse the Mott gap down and drive off-equilibrium the insulator into a metastable metal phase [4].\\[4pt] [1] M. Schir\'{o} and M. Fabrizio, Phys. Rev. Lett. \textbf{105}, 076401 (2010).\\[0pt] [2] M. Schir\'{o} and M. Fabrizio, Phys. Rev. B \textbf{83},165105 (2011).\\[0pt] [3] M. Sandri, M. Schir\'{o} and M. Fabrizio, Phys. Rev. B \textbf{86}, 075122 (2012). \\[0pt] [4] M. Sandri and M. Fabrizio, arXiv:1410.4442. [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:48AM |
Y18.00003: Thermalization and long-time behavior of nonequilibrium correlated quantum systems Invited Speaker: Herbert F. Fotso Nonequilibrium dynamical mean field theory and nonequilibrium self-consistent strong coupling expansion[1] are used to study the relaxation of correlated quantum systems driven out of equilibrium by DC electric fields[2]. Both the Falicov-Kimball and the Hubbard model are found to exhibit regimes of monotonic or oscillatory themalization as well as regimes where they evolve in a monotonic or oscillatory manner towards a non-thermal state. This suggests that driven quantum systems have a richer behavior than their quenched counterparts and that integrability does not play as critical a role. In the monotonic thermalization scenario, the system evolves through successive quasi-thermal states and it is possible to extrapolate its long time properties from its transient; bridging the gap between the transient and the steady state with very little computational cost. Furthermore, regardless of the relaxation scenario, it is interesting to ask how the particles are distributed as the system evolves in time. We will show that non-trivial parameter-dependent patterns are formed when the system is visualized in momentum space [3]. These features should be observable in current cold atom experiments. \\[4pt] [1] K. Mikelsons, J. K. Freericks, and H. R. Krishnamurthy, Phys. Rev. Lett. 109 260402 (2012).\\[0pt] [2] H. Fotso, K. Mikelsons and J. K. Freericks, Scientific Reports 4, 4699 (2014).\\[0pt] [3] H. Fotso, J. Vicente and J. Freericks, arXiv:1310.6350. [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:24AM |
Y18.00004: New Perspectives for Time-Evolution with DMRG Invited Speaker: Ulrich Schollwoeck In the last 10 years, time-evolution with DMRG has revealed itself to be a very powerful technique for low-dimensional strongly interacting quantum systems both near and far from equilibrium. We show how new techniques, mainly based on the use of Chebyshev polynomials allowing to use DMRG for obtaining real-frequency spectral information in multi-band DMFT calculations, also allow to use it as an impurity solver for far-from-equilibrium DMFT in a Hamiltonian formulation, strongly increasing the time range of non-equilibrium DMFT, and to attack time-evolutions efficiently in far from equilibrium settings. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 11:00AM |
Y18.00005: Nonequilibrium Dynamical Mean Field Theory for Inhomogeneous and Photo-Excited Systems Invited Speaker: Philipp Werner Photodoping of a Mott insulator triggers a nonequilibrium phase transition from a correlation induced insulating state to a nonthermal conducting state with electron- and hole-like carriers. Using the nonequilibrium extension of (inhomogeneous) dynamical mean field theory\footnote{J. K. Freericks, V. M. Turkowski, and V. Zlatic, ``Nonequilibrium Dynamical Mean-Field Theory,'' Phys. Rev. Lett. 97, 266408 (2006).}$^,$\footnote{M. Eckstein and P. Werner, ``Nonequilibrium dynamical mean field simulation of inhomogeneous systems,'' Phys. Rev. B 88, 075135 (2013).} in combination with a strong-coupling impurity solver\footnote{M. Eckstein and P. Werner, ``Nonequilibrium dynamical mean-field calculations based on the non-crossing approximation and its generalizations,'' Phys. Rev. B 82, 115115 (2010).} we study the relaxation and diffusion of photo-doped carriers in Mott insulating bulk systems and hetero-structures. In large-gap insulators, the life-time of the carriers depends exponentially on the gap size,\footnote{M. Eckstein and P. Werner, ``Thermalization of a pump-excited Mott insulator,'' Phys. Rev. B 84, 035122 (2011).} while in small-gap insulators, strongly pulse-energy dependent impact ionization processes lead to a double-exponential relaxation.\footnote{P. Werner, K. Held and M. Eckstein, ``Role of impact ionization in the thermalization of photo-excited Mott insulators,'' arXiv:1408.3425.} In the paramagnetic phase, the photo-doped carriers spread through the insulator in a diffusive manner, while the scattering with an antiferromagnetic background leads to a rapid loss of kinetic energy.\footnote{P. Werner, N. Tsuji, and M. Eckstein, ``Nonthermal symmetry broken states in the strongly interacting Hubbard model,'' Phys. Rev. B 86, 205101 (2012).} In the presence of strong fields, as realized e. g. in polar heterostructures, the ability to dissipate energy locally in an antiferromagnetic system enables fast carrier transport.\footnote{M. Eckstein and P. Werner, ``Ultrafast separation of photo-doped carriers in Mott antiferromagnets,'' Phys. Rev. Lett. 113, 076405 (2014).} These insights should be relevant for designing Mott insulating solar cells\footnote{E. Assmann, P. Blaha, R. Laskowski, K. Held, S. Okamoto, and G. Sangiovanni, ``Oxide Heterostructures for Efficient Solar Cells,'' Phys. Rev. Lett. 110, 078701 (2013).} and light-controlled devices which operate on an ultra-fast timescale. [Preview Abstract] |
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