Sample Rotation as a New Method for Identifying the FFLO State in λ-(BETS)₂GaCl₄

The FFLO state is a state of inhomogeneous superconductivity that exists at high magnetic fields. In specific crystals, the limit, H_p, where Cooper pairs begin to break due to paramagnetic effects is reached before the ultimate critical field, H_c2. We will present rf penetration depth measurements on the quasi-2D organic superconductor λ-(BETS)₂GaCl₄ (BETS) using a tunnel diode oscillator. The quasi-2D structure of BETS makes features such as H_c2, the FFLO transition, and vortex effects like the lock-in effect highly sensitive to the angle that the conduction planes make with the applied field. By rotating the sample in a constant external magnetic field, we can locate points on the FFLO phase line that are not easily identifiable via traditional field sweeps, and will use these data to show a Field—Angle FFLO phase diagram at very low temperature (60mK). Using this new identification technique to supplement existing field sweep data, we have started to construct a full 3D Field—Angle—Temperature phase diagram of the FFLO state.