FFLO Phase in Layered Organic Superconductors

Abstract

Superconductivity is one of the most intriguing topics in solid state physics. In general, spin-singlet Cooper pairs in superconducting phases are broken by the Zeeman effect, which gives the Pauli limit. However, Cooper pairs can theoretically survive even above the Pauli limit in special conditions, which is the so-called FFLO phase. So fat, extensive efforts have been devoted to the discovery of the FFLO phase but vortex melting transitions have given rise to considerable ambiguity in the interpretation of the experimental data. By comprehensive magnetocaloric and torque studies of the FFLO phase in a highly two-dimensional organic superconductor, the FFLO phase transition is observed near the Pauli limit, clearly distinct from the vortex melting transitions. The results provide convincing evidence of the FFLO phase in high magnetic fields.