Abstract

The question of fermionic superfluidity with imbalanced spin populations has intrigued physicists for many decades. Bardeen, Cooper and Schrieffer (BCS) described the superconducting state as a condensate of electron pairs carrying opposite spin. However, an applied magnetic field tends to align the electron spins, thereby putting a “stress” on the fully paired state. This eventually leads to depairing and the breakdown of superconductivity, known as the Clogston limit. In typical superconductors, this limit is never reached: Magnetic fields are expelled from the superconductor via the Meissner effect, and can only enter as quantized magnetic flux lines (vortices). At a critical magnetic field H_c2 much smaller than the Clogston critical field, superconductivity is quenched.

© 2007 IEEE