Condensed Matter Physics

Professor Anton Vorontsov, Montana State University

Title: Heat transport in domain walls of unconventional superconductors


Thermal transport is a powerful superconductivity probe requiring close synergy between experiment and theoretical support. I will describe general theoretical approach to calculation of energy transport in inhomogeneous superconductors. Such nonuniform states appear near pairbreaking surfaces, in confinement, or due to competing effects as in the Fulde-Ferrell-Larkin-Ovchinnikov state. We will look at the example of a domain wall in the superconducting order parameter and heat transport across and along the domain wall in d-wave and chiral superconductors.

The Andreev bound states in the nonuniform region affect the heat transport in several ways: (i) they result in Andreev reflection processes due to spatially-varying quasiparticle spectrum, and (ii) they hybridize with the impurity band producing a local transport environment with properties very different from those in a uniform superconductor. As a consequence, heat transport becomes highly anisotropic and explicitly non-local, with new features that depend on temperature, magnetic field, disorder and order parameter symmetry. For example, strongly scattering impurities result in a more efficient low-temperature heat transport than that in the uniform superconducting state.

Host: Jim Sauls

Speaker: Professor Mark Dykman, Michigan State University

Title: Floquet dynamics of nonlinear oscillators and time-translation symmetry breaking

Abstract: A periodically driven system has discrete time-translation symmetry with the period of the driving. Its quantum dynamics is described in terms of the Floquet states. Generally, if the system is in a Floquet state, its dynamical variables oscillate with the period of the driving. Recently much interest have attracted systems where the time symmetry is broken, the “time crystal” effect. Nonlinear oscillators provide an ideal platform for studying this effect. A familiar example is parametric resonance: when a dissipative oscillator is modulated close to twice the eigenfrequency, the period of the parametrically excited vibrations is twice the modulation period. We will show that the symmetry breaking may occur also in the quantum coherent regime and discuss the transition to the incoherent regime. The results fill in the gap between the topologically protected broken-symmetry states in extended systems and multiple-period states in dissipative systems.

Hosts: Jim Sauls, Jens Koch

Professor Alex Levchenko, University of Wisconsin-Madison

Title: Anomalous quantum transport - Hall, Kerr and Josephson effects

Abstract: I will review mechanisms of the anomalous Hall effect using the model of massive Dirac fermions as a guiding example. Extensions of the theory to the case of chiral p-wave superconductors will be presented in the context of the Kerr effect. We will also discuss how multi-terminal Josephson junctions can realize quantized anomalous Hall like responses which are governed by the Berry fluxes of the band topology harbored by Andreev states. The latter realize Weyl-like semi-metallic phases.

Host: Jim Sauls


Dr. Vanessa Graber: TBA

November 9, 2017, 4:00 PM - 5:30 PM

Dr. Vanessa Graber, McGill Space Institute at McGill University

Title: TBA

Abstract: TBA

Hosts: Vicky Kalogera, Jim Sauls