Pressure dependence of the Fulde-Ferrell-Larkin-Ovchinnikov state in CeCoIn5

Pressure studies of the thermodynamics of CeCoIn5 under magnetic fields H∥c and H∥ab have been made up to P=1.34GPa. We recorded the signature of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state for all pressures when H∥ab. Also remarkably, the FFLO regime suddenly expands for P=1.34GPa. With the help of a microscopic theory for d-wave superconductivity, we have extracted the gyromagnetic ratio g and the Fermi velocities va and vc. Our study is the first evidence for the existence of the FFLO state away from the influence of the antiferromagnetic fluctuations. We find a close parallel between the T-P phase diagram of CeCoIn5 and the T-x phase diagram of the high-Tc cuprates, where x is the hole concentration.