Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session H1: Spin-Liquid Insulators and Strongly Correlated Superconductors |
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Sponsoring Units: DCMP Chair: Matthew Fisher, UC-Santa Barbara Room: LACC 152 |
Tuesday, March 22, 2005 8:00AM - 8:36AM |
H1.00001: Dynamical Mean Field Approach to Charge Excitations in manganites Invited Speaker: The physics of the ``colossal" magnetoresistance manganites is reviewed with particular attention given to atomic-scale physics related to charge dynamics. Issues covered include whether the materials should be viewed as strongly correlated (is the ``U" or charge transfer energy large enough), whether the Hunds coupling is large enough for ``double exchange" physics to be relevant, and whether ``polaron physics" is important. The origin of the observed isotope effect is disucssed. The implications of the observed large transfer of spectral weight as temperature is varied through the magnetic transition is outlined. Open issues are summarized. The talk is based in part on Phys Rev B68, 115111 (2003) (written with B. Michaelis); in part on Phys Rev B65 224301 (2002) (written with A. Deppeler) and in part on unpublished work. The research reported here was supported by NSF through the MRSEC program. [Preview Abstract] |
Tuesday, March 22, 2005 8:36AM - 9:12AM |
H1.00002: Exotic Phases and Fractionalization in Frustrated Quantum Magnets Invited Speaker: Recent work shows that excitations with fractional quantum numbers can emerge in two and three dimensions in zero magnetic field in quantum systems with competing interactions. This can occur throughout an entire ``exotic'' phase or in the vicinity of isolated quantum critical points between conventional phases. Such phases or critical points require thinking beyond the usual paradigms of mean field theory and broken symmetry. The talk will outline efforts to identify and understand such phenomena in simple physical models appropriate to semi-realistic quantum magnets, cold trapped atoms, and strongly correlated superconductors. [Preview Abstract] |
Tuesday, March 22, 2005 9:12AM - 9:48AM |
H1.00003: Spin Liquids, Valence Bond Crystals and Cantor Deconfinement in Quantum Dimer Models Invited Speaker: Quantum dimer models capture the low energy dynamics of valence bond phases of quantum magnets. I will review results on their phase diagrams on a variety of lattices in two and three dimensions. These exhibit $Z_2$ and $U(1)$ resonating valence bond liquids, a variety of valence bond crystals and a region with a devil's staircase of commensurate and incommensurate crystals which support deconfinement of spinons on a Cantor set. I will also describe the construction of $S=1/2$ Heisenberg Hamiltonians which precisely reproduce these phase diagrams. [Preview Abstract] |
Tuesday, March 22, 2005 9:48AM - 10:24AM |
H1.00004: Novel Inhomogeneous Metallic Phase in a Disordered Mott Insulator in Two Dimensions Invited Speaker: We show that with increasing site disorder, the spectral gap in a 2D Mott insulator closes beyond a critical disorder strength V1 while antiferromagnetism persists up to a higher disorder strength V2. Most unexpectedly, in the intermediate disorder regime between V1 and V2, we find that the system is metallic and sandwiched between the Mott insulator below V1 and an Anderson type insulator above V2. The unusual metal is formed when the spectral gap gets destroyed locally in regions where the disorder potential is high enough to overcome the interelectron repulsion. Puddles with enhanced charge fluctuations are generated which percolate with increasing disorder, resulting in a spatially inhomogeneous metallic phase. \newline \newline D. Heidarian and N. Trivedi, Phys. Rev. Lett. 93, 126401 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 10:24AM - 11:00AM |
H1.00005: Bose Metal in 2D Invited Speaker: Bosons are thought to exist in two quite distinct ground states: 1) localized in a Mott insulator or 2) condensed in a superconductor. However, recent experiments point to a third intriguing possibility: a metal with a finite resistivity at zero temperature. The Bose metallic phase appears to be quite robust and is observed in a wide variety of thin films which should nominally exihibit only insulating or superconducting phases. I will review the standard theoretical framework used to understand the insulator-superconductor transition, the recent experimental results and I will show quite generally how bosons in the presence of disorder can form a metallic state. The metallic state is rather weird, however. The phase degrees of freedom are glassy and it is the low-lying degrees of freedom in the glassy state that mediate the metallic state. An explicit calculation reveals that the phase stiffness vanishes, thereby confirming that the state found here is distinct from a superconductor. The relevance to the vortex glass state of the cuprates in which recent experiments suggest a transition to such a state occurs without the vanishing of the linear resistivity will be discussed. Relevant papers: 1.) P. Phillips and D. Dalidovich, Science {\bf 302}, 243 (2003). 2.) P. Phillips and D. Dalidovich, Phys. Rev. B {\bf 68}, 104427 (2003). 3.) D. Dalidovich and P. Phillips, Phys. Rev. Lett. {\bf 89}, 27001 (2002). [Preview Abstract] |
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