Reentrant superconductivity on a triangular lattice: application to cobalt oxide superconductor

Abstract

It is possible that a triplet pairing is responsible for superconductivity in the recently discovered wet cobalt-based compounds. In such a case, the Zeeman coupling does not put limits on the upper critical field ( H c 2 ) and its value is determined solely by the diamagnetic effects. In the absence of the Pauli pair-breaking mechanism reentrant superconducting phase may set on. It was shown by Rasolt and Tešanović that the Landau level quantization in isotropic superconductors could enhance superconductivity in a very strong magnetic field. In the present paper, we investigate superconducting phase transition in Na x CoO 2 · y H 2 O in the presence of a strong magnetic field. Special attention is put on a possible occurrence of the reentrant phase.