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.