Unconventional superconductivity in UPt 3 low field AC susceptibility studies

Abstract

Low-field AC susceptibility measurements have been carried-out on single-crystalline samples of the unconventional superconductor UPt 3 and on UPt 3 doped with 11% boron. Both components of the susceptibility, χ′ ( T) and χ″ ( T) have been found to depend strongly on the AC field amplitude, on the superimposed DC field (up to 200 Oe), and on the orientation of the field with respect to crystallographic axes. A discussion of the experimentally determined penetration depth close to T c is presented, leading to the conclusion that the mechanism described by Campbell makes a large contribution to the field penetration into the superconductor. A phase diagram constructed on the basis of field penetration into the bulk sample is only partly in agreement with H c1 ( T) results published earlier. We argue that a vortex-glass state may be formed in UPt 3 close to T c, due to the coupling between the AF and unconventional SC order parameters.