Abstract:
The dc Josephson effect refers to the dissipationless electrical current
-- the supercurrent -- that can be sustained across a weak link connecting two bulk
superconductors. This effect probes the nature of the superconducting state,
which depends crucially on spatial dimensionality. For bulk (i.e. three-dimensional)
superconductors, the superconductivity is most robust, and the Josephson effect is
sustained even at nonzero temperature. However, in wires and thin films, thermal
and quantum fluctuations play a crucial role. In superconducting wires, these
effects qualitatively modify the electrical transport across a weak link. Despite
several recent experiments involving weak links between thin-film superconductors,
little theoretical attention has been paid to the electrical conduction in such systems.
I will discuss recent work [1,2] in which a system of two superconducting thin films
connected by a point contact was analyzed. Remarkably, the Josephson effect is absent
at nonzero temperature. The point contact resistance is nonzero and varies with
temperature in a nearly activated fashion, with a universal energy barrier set by the
superfluid stiffness characterizing the films. I will discuss the derivation of this
result and try to give some intuition for the underlying physics, which can best be
pictured in terms of quantum phase slip events. In addition, I will discuss considerations
relevant to future experimental tests of the predicted behavior.
[1] Michael Hermele, Gil Refael, Matthew P. A. Fisher and Paul M. Goldbart, Nature Physics 1, 117 (2005). (cond-mat/0508301)
[2] Michael Hermele, Gil Refael, Matthew P. A. Fisher and Paul M. Goldbart,
cond-mat/0511210 (2005).