Date/Time
Date(s) - 06/02/2006
2:30 pm - 3:30 pm

Title: Quasiparticles and Vortices in d-wave Superconductors

Speaker: Dr. Oskar Vafek

Institute: Stanford University
Department of Physics

Location: ABB 102

Description:

Interactions between quantized vortices and quasipartices of an extreme type-II d-wave superconductor will be discussed. In an external magnetic field, the vortices form an Abrikosov lattice, with a lattice spacing much smaller than the penetration depth. Unlike in an s-wave superconductor, the states near the Fermi level are extended and form dispersive bands. In 2 dimensions and in the absence of any fine tuning, the spectrum is gapped for an inversion symmetric vortex lattice. The gap has a nontrivial topological character. If fine tuned to the point of exact particle-hole symmetry, a form of an index theorem can be employed to count the number of bulk zero energy states non-perturbatively. Remarkably, for singly quantized hc/2e vortices, which interact with the quasiparticles via an additional topological Z2 term, the number of zero modes generally differs from the number in the case of hc/e vortices or in the absence of the field, despite identical point group symmetries. This fact will then be discussed in the context of Wen’s notion of quantum order.