Probing the FFLO State in Quasi-2D Organic Superconductors using Sample Angular Rotations*

Organic superconductors can be prime candidates to investigate the FFLO state, an exotic, inhomogeneous superconducting state existing at high magnetic fields above the paramagnetic limit, H_p, where superconductivity is normally destroyed. Our layered organic crystals are highly anisotropic and have quasi-2D structures, so the angle that their conduction planes make with an external B-field greatly affects features such as H_c2, the FFLO phase transition, and vortex dynamics such as the lock-in effect. Thus, we merge traditional Field- and Temperature-analysis with sample rotations to explore these features as a function of angle. We will present rf-penetration depth measurements made using a tunnel diode oscillator circuit on λ-(BETS)₂GaCl₄ and κ-(ET)₂Cu(NCS)₂ and compare our angular data to theoretical modeling. Combining results from field sweeps and angle rotations in pulsed- and DC-fields, respectively, we will show a preliminary 3D phase diagram of the FFLO state in Field-Angle-Temperature phase space.