Date: Wednesday, Nov 14, 2012
Venue: Conference Hall 322, Science Building, Tsinghua University
10:15am – 11:15am Dr. Edward Taylor ( McMaster University )
Title: the most unconventional superconductor: Sr2RuO4. After 18 years, what do we know?
Abstract: 18 years after the discovery of superconductivity in the perovskite Sr2RuO4, basic questions about the nature of the superconducting order parameter remain. Almost immediately after the discovery of superconductivity, it was realized theoretically that it might be a chiral p-wave state, the solid-state analogue of the A-phase of superfluid Helium 3. If so, it would be the only known example so far of this exotic time-reversal symmetry-breaking state in electronic systems.
After more than a decade and a half of intense experimental effort, however, the question of whether Sr2Ru04 is chiral p-wave still lacks a definitive answer. In this talk, I will review some of these experiments as well as theory, highlighting signatures of time-reversal symmetry-breaking coming from Kerr rotation measurements as well as the seeming absence of topological time-reversal symmetry-breaking edge currents implied by SQUID microscopy experiments. I will argue that the multiband nature of Sr2RuO4 and its large spin-orbit coupling will likely play a central role in interpreting these experiments.
References:
1.) E. Taylor & C. Kallin, Anomalous Hall conductivity of clean Sr2RuO4 at finite temperatures. arXiv: 1208.2699.
2.) E. Taylor & C. Kallin, Intrinsic Hall Effect in a Multiband Chiral Superconductor in the Absence of an External Magnetic Field, PRL 108, 157001 (2012).
11:15am - 12:15pm Prof. Zheng-Yu Weng ( Tsinghua University )
Title: Self-localization of a single hole in Mott antiferromagnets
Abstract: Anderson localization -- quantum suppression of carrier diffusion due to disorders -- is a basic notion of modern condensed matter physics. Here I will talk about a novel localization phenomenon totally contrary to this common wisdom. Strikingly, it is purely of strong interaction origin and occurs without the assistance of disorders. Specifically, by combined numerical (density matrix renormalization group) method and analytic analysis, we show that a single hole injected in a quantum antiferromagnetic ladder is generally self-localized even though the system respects the translational symmetry. The localization length is found to monotonically decrease with the increase of leg number, indicating stronger self-localization in the two-dimensional limit. We find that a peculiar coupling between the doped charge and the quantum spin background causes quantum interference among different hole paths. The latter brings the hole's itinerant motion to a halt, a phenomenological analogy to Anderson localization. Our findings are opposite to the common belief of the quasiparticle picture for the doped hole and unveil a completely new paradigm for lightly doped Mott insulators.
3:15pm - 4:15pm Prof. Mohit Randeria ( The Ohio State University )
Title: Viscosity of Strongly Interacting Fermions
Abstract: Transport in strongly interacting quantum fluids is of great interest in diverse areas of physics — condensed matter, black holes and string theory, quark-gluon plasmas and cold atoms — which, at first sight, appear to have little in common. In this talk I will focus on the bulk and shear viscosity of ultracold Fermi gases, for which the most controlled experiments are possible. I will first discuss connections between transport and thermodynamics across the entire BCS-BEC
crossover using exact sum rules [1]. I will describe implications for the strongly interacting unitary regime in 3D where scale invariance leads to particularly interesting predictions. I will then discuss recent results [2] that give insight into why experiments on 2D Fermi systems appear to show scale invariance at low energies.
[1] E. Taylor and M. Randeria, Phys. Rev. A 81, 053610 (2010)
[2] E. Taylor, M. Randeria; Phys. Rev. Lett. 109, 135301 (2012)
4:15pm - 5:15pm Tin-Lun (Jason) Ho (The Ohio State University and Tsinghua)
Title: The Bosonic Quantum Hall States
Abstract: It has been a long sought goal in cold atom research to realize bosonic quantum Hall states. This search is now further intensified due to some aggressive research initiatives recently announced in the United States. In this talk, I point out a natural and practical way to generate the bosonsic Laughlin state and Pfaffian state. This method is a novel version of "BEC-BCS crossover" captured by a number of mathematical identifies discovered in the 16th century. If time permits, I shall also describe the new research initiatives in the United State that actively bring together the condensed matter and the cold atom communities to pursue some highly ambitious goals.
