The anomalous superconducting phase diagram of (BEDO-TTF)(2)ReO4 center dot H2O.

We have measured the critical magnetic fields in the quasi 2D superconducto r (BEDO-TTF)ReO4.H2O as a function of temperature with the magnetic field p erpendicular and parallel to the conducting planes. A sharp positive change in the curvature, or kink, in the H-T phase line, similar to one in the ph ase diagram of the superconductor lambda-(BETS)(2)GaCl4, occurs in the low temperature part of the phase diagram near T/T-c = 0.4. These kinks in the H-T phase line could be the signature of a change in the superconducting or der parameter. We discuss other possibilities, such as magnetic transitions , and why they are less likely to exist in these salts. To support our clai ms we also present recent data showing part of the H-T phase diagram of lam bda-(BETS)(2)GaCl4 with the applied magnetic field parallel to the conducti ng planes.