Bulletin of the American Physical Society
78th Annual Meeting of the Southeastern Section of the APS
Volume 56, Number 9
Wednesday–Saturday, October 19–22, 2011; Roanoke, Virginia
Session CB: Strongly Correlated Systems |
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Chair: Vito Scarola, Virginia Polytechnic Institute and State University Room: Crystal Ballroom B |
Thursday, October 20, 2011 10:45AM - 11:15AM |
CB.00001: Strong Correlation Effects in Fullerene Molecules and Solids Invited Speaker: Fullerenes (C20, C36, C60) are a family of Carbon cage molecules that have exactly twelve pentagons. The most famous Fullerene is C60 (``bucky ball''), which when being doped with three electrons per molecule will exhibit superconductivity. Here we describe electronic structures of these molecules with a tight-binding Hubbard model and solve the model with quantum Monte Carlo simulations and exact diagonalization method. We will show how the electronic correlation gets stronger as the molecule becomes more curved, how the strong electronic correlations change the Huckel molecular energy levels, and how we compare the single-particle excitation spectrum for the C60 molecular solid to the photoemission experiments. [Preview Abstract] |
Thursday, October 20, 2011 11:15AM - 11:45AM |
CB.00002: Interlay of Quantum Criticality and Geometric Frustration in Columbite Invited Speaker: CoNb$_2$O$_6$ is a remarkable magnetic material. The interplay between two of the most exciting features of correlated quantum physics, quantum criticality and geometric frustration, results in a rich phase diagram which reflects the fundamental underlying quantum many-body physics in this complex oxide material. Many aspects of the theoretically calculated phase diagram and expectations for quantum criticality have already been observed in beautiful neutron scattering experiments on this material.\\[4pt] Ref: \textit{Interplay of Quantum Criticality and Geometric Frustration in Columbite}, SungBin Lee, Ribhu K. Kaul, Leon Balents, Nature Physics {\bf 6}, 702-706 (2010) [Preview Abstract] |
Thursday, October 20, 2011 11:45AM - 12:15PM |
CB.00003: Ultrafast Dynamics in Vanadium Dioxide: Separating Spatially Segregated Mixed Phase Dynamics in the Time-domain Invited Speaker: In correlated electronic systems, observed electronic and structural behavior results from the complex interplay between multiple, sometimes competing degrees-of- freedom. One such material used to study insulator-to-metal transitions is vanadium dioxide, which undergoes a phase transition from a monoclinic-insulating phase to a rutile-metallic phase when the sample is heated to 340 K. The major open question with this material is the relative influence of this structural phase transition (Peirels transition) and the effects of electronic correlations (Mott transition) on the observed insulator-to-metal transition. Answers to these major questions are complicated by vanadium dioxide's sensitivity to perturbations in the chemical structure in VO$_2$. For example, related V$_x$O$_y$ oxides with nearly a 2:1 ratio do not demonstrate the insulator-to- metal transition, while recent work has demonstrated that W:VO$_2$ has demonstrated a tunable transition temperature controllable with tungsten doping. All of these preexisting results suggest that the observed electronic properties are exquisitely sensitive to the sample disorder. Using ultrafast spectroscopic techniques, it is now possible to impulsively excite this transition and investigate the photoinduced counterpart to this thermal phase transition in a strongly nonequilibrium regime. I will discuss our recent results studying the terahertz-frequency conductivity dynamics of this photoinduced phase transition in the poorly understood near threshold temperature range. We find a dramatic softening of the transition near the critical temperature, which results primarily from the mixed phase coexistence near the transition temperature. To directly study this mixed phase behavior, we directly study the nucleation and growth rates of the metallic phase in the parent insulator using non-degenerate optical pump-probe spectroscopy. These experiments measure, in the time- domain, the coexistent phase separation in VO$_2$ (spatially separated insulator and metal islands) and, more importantly, their dynamic evolution in response to optical excitation. [Preview Abstract] |
Thursday, October 20, 2011 12:15PM - 12:45PM |
CB.00004: Superfluidity in bilayer systems of cold polar molecules Invited Speaker: An exciton is a quasiparticle state formed by an electron bound to a ``hole.'' Many years ago it was proposed theoretically that a population of excitons can condense into a spontaneously broken symmetry ground state characterized by excitonic superfluidity. The quest for the experimental realization of the exciton condensate has lasted decades. Recently bilayer systems have emerged as some of the most promising systems in which this state can be realized. The physics of exciton condensation in bilayer systems is very general. In this talk I will present the theory of ``excitonic condensation'' and spontaneous interlayer superfluidity in cold polar molecules bilayers [1] that because of the great control characteristic of cold atom systems and their intrinsic lack of disorder are ideal systems to study exciton condensates. \\[4pt] [1] R. M. Lutchyn, E. Rossi, S. Das Sarma {\em Spontaneous interlayer superfluidity in bilayer systems of cold polar molecules}, Phys. Rev. A, {\bf 82}, 061604(R) (2010). [Preview Abstract] |
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