Superconductivity is one of the most intriguing topics in solid state physics. Generally, the superconducting Cooper pairs are broken by the Zeeman effect, which gives the so-called Pauli paramagnetic limit H_Pauli. However, when the superconductivity is in the clean limit and the orbital effect is strongly quenched, the Cooper pairs can survive even above H_Pauli, which is the so-called Fulde and Ferrell, and Larkin and Ovchinnikov (FFLO) phase. Extensive efforts have been devoted to the discovery of the FFLO phase. However, vortex phase transitions have given rise to considerable ambiguity in the interpretation of the experimental data. Here, we report comprehensive magnetocaloric and torque studies of the FFLO phase transition in a highly two-dimensional organic superconductor. We observe the FFLO phase transition clearly distinct from vortex melting transitions. The phase diagram provides crucial information on the stability of the FFLO phase in magnetic fields.

超导性是固态物理学中最有趣的主题之一。通常，超导库珀对会因塞曼效应而破裂，从而产生所谓的Pauli顺磁极限H _Pauli。但是，当超导处于纯净极限并且轨道效应被强烈淬灭时，即使在H _Pauli以上，Cooper对也可以生存。，即所谓的Fulde和Ferrell以及Larkin和Ovchinnikov（FFLO）阶段。已经为发现FFLO阶段付出了巨大的努力。但是，涡旋相变在解释实验数据时引起了很大的歧义。在这里，我们报告了在高二维有机超导体中FFLO相变的全面磁热和转矩研究。我们观察到FFLO相变明显不同于涡旋熔融转变。相图提供了有关FFLO相在磁场中的稳定性的重要信息。