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

The FFLO state is a state of inhomogeneous superconductivity that exists at high magnetic fields. In specific crystals, the point where Cooper pairs begin to break due to paramagnetic effects, H_p, happens before reaching the ultimate critical field, H_c2. We will present rf penetration depth measurements on the quasi-2D layered 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 phase transition, and vortex effects like the lock-in effect highly sensitive to the angle that the conduction planes make with the external 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 field sweeps. In addition, we will visualize the FFLO phase transitions in BETS by showing a Field−Angle phase diagram at very low temperature (60 mK). With the addition of this new technique, we have begun constructing a full 3D Field−Angle−Temperature phase diagram of the FFLO state.