Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session F13: New Developments in the Study of Inhomogeneous Strongly Correlated Quantum SystemsInvited Session
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Sponsoring Units: DCOMP DAMOP Chair: Mark Jarrell, Louisiana State University Room: 309 |
Tuesday, March 15, 2016 11:15AM - 11:51AM |
F13.00001: New theoretical tools for quantum glasses, with and without quenched disorder Invited Speaker: Louk Rademaker Even though most solid materials are disordered or glasslike, our understanding of such non-equilibrium phases of matter is meager. Our task is thus to develop new tools to understand the nature of quantum glasses. These can be characterized into two classes: with or without quenched disorder. Interacting spin or electron models with quenched disorder are known to exhibit many-body localization (MBL). We discuss a new method based on a Hilbert-space preserving RG scheme to find the integrals of motion for an interacting system. We used this approach to numerically study MBL phases and the corresponding transition. \\ On the other hand, we discuss the possibility of self-generated electron glassiness in the absence of quenched disorder. Such structural quantum glasses, requiring geometric frustration and long-range interactions, are in many ways similar to the quenched disorder glasses. We will discuss the soft gap in the density of states, which is now related to short-range ‘frozen’ density correlations. Using both numerical and analytic arguments we find Arrhenius-type slow relaxation and stretched exponential behavior. \\ {\bf References:} \\ - L. Rademaker, A. Ralko, S. Fratini and V. Dobrosavljevic, Avoiding Stripe Order: Emergence of the Supercooled Electron Liquid, arXiv:1508.03065 (2015). \\ - L. Rademaker, M. Ortuno, Explicit Local Integrals of Motion for the Many-Body Localized State, arXiv:1507.07276 (2015). \\ - S. Mahmoudian, L. Rademaker, A. Ralko, S. Fratini and V. Dobrosavljevic, Glassy dynamics in geometrically frustrated Coulomb liquids without disorder, Phys. Rev. Lett. 115, 025701 (2015); arXiv:1412.4441. \\ - L. Rademaker, Y. Pramudya, J. Zaanen and V. Dobrosavljevic, Influence of long-range interactions on charge ordering phenomena on a square lattice, Phys. Rev. E 88, 032121 (2013); arXiv:1306.4765. [Preview Abstract] |
Tuesday, March 15, 2016 11:51AM - 12:27PM |
F13.00002: Quench and Transport Dynamics in Disordered Atomic Hubbard Lattices Invited Speaker: Brian DeMarco I will give an overview of our experiments using ultracold atom gases trapped in optical lattices to probe transport, dynamics, and relaxation in disordered Hubbard models. By introducing disorder to naturally clean optical lattices using focused optical speckle, we realize variants of the disordered Bose- and Fermi-Hubbard models. In these systems, the distribution of Hubbard parameters is fully known, and the ratio of characteristic energy scales is completely tunable. I will discuss two measurements. In the first, we observe localization via transport measurements in the metallic regime of the Fermi-Hubbard model. We observe three phenomena consistent with many-body localization: localization at non-zero temperature, localization across a range of temperatures, and interaction-induced delocalization. These measurements show agreement with a mean-field theory in a limited parameter regime. In a separate experiment using bosonic atoms, we measure excitations following a quantum quench of disorder. Via comparison to state-of-the-art quantum Monte Carlo calculations that capture all aspects of the experiments---including all the particles---we show that the onset of excitations corresponds to the superfluid--Bose-glass transition. I will discuss how this behavior is reminiscent of the quantum Kibble-Zurek effect. [Preview Abstract] |
Tuesday, March 15, 2016 12:27PM - 1:03PM |
F13.00003: The role of weak interactions on the mobility-edge of strongly disordered electron systems Invited Speaker: Chinedu Ekuma New insights into the nature of the mobility edge of a weakly correlated, disordered Anderson spectra will be presented within the typical medium dynamical cluster approximation (TMDCA). The TMDCA systematically incorporates non-local spatial correlations (beyond the single-site approximations) treating the disorder to all orders and the interacting, non-local cluster self-energy up to second order in the perturbation expansion of the interactions, $U$. An arbitrary small interaction is found to lead to an exponential fast crossover of the sharp mobility edge that separates the localized and extended states in the non-interacting regime below the critical disorder strength $W_c^{U=0}$ whenever the chemical potential of the non-interacting typical density of states is below the mobility edge energy. This smearing of the mobility edge is ascribed to the inelastic scattering due to $U$. However, as the chemical potential, $\mu$ approaches the smeared edge, reduction of the phase space for scattering by $U$ causes the edge to once again become sharp. A concomitant soft-pseudogap is found at energy, $\omega=0$ independent of filling, which is linear rather than quadratic in $\omega$, due to the lack of momentum conservation. The method is demonstrated on realistic low-dimensional structures. [Preview Abstract] |
Tuesday, March 15, 2016 1:03PM - 1:39PM |
F13.00004: Precise finite-temperature properties of disordred strongly-correlated electronic systems Invited Speaker: Ehsan Khatami The interplay between disorder and electronic interactions in quantum many-body systems is not well understood. Experiments with ultracold atoms on optical lattices hold a great promise for exploring the different competing phases that arise in these systems by simulating disordered quantum lattice models in the presence of interactions. However, these experiments often rely on precise and approximate-free results from numerical calculations for various static and dynamic properties of these models in order to characterize the experimental systems. In this talk, I will present recently obtained data for the thermodynamic properties and magnetic correlations of the disordered three-dimensional Hubbard model using the determinant quantum Monte Carlo. I will also discuss new techniques within the numerical linked-cluster expansions that allow for fast and precise calculation of finite-temperature properties of disordered systems in the thermodynamic limit. [Preview Abstract] |
Tuesday, March 15, 2016 1:39PM - 2:15PM |
F13.00005: Properties of dirty bosons in disordered optical lattices Invited Speaker: Ushnish Ray Disorder is ubiquitous in nature and its presence can lead to fascinating phenomena such as Anderson localization, Griffiths mechanisms and glassiness. These types of behavior have profound consequences on low temperature ordered phases that are difficult to study, particularly due to lack of controllable disorder. Recent advances in ultra-cold atomic systems have made it possible to make significant progress in overcoming such challenges -- making direct comparisons with large scale Quantum Monte-Carlo techniques a possibility. I will talk about the disordered Bose-Hubbard model and the equilibrium properties of the domains that arise in trapped systems. I will show how they correspond to phases and explore the consequences of finite temperature and strong correlations. These aspects will be used to explain the observations of experimental measurements. In particular, I will highlight results of a recent collaborative enterprise that show excellent agreement between theory and experiment. [Preview Abstract] |
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