Superconducting phase diagram and FFLO signature in λ-(BETS)2GaCl4 from rf penetration depth measurements

Abstract

We report the phase diagram of λ-(BETS)2GaCl4 [where BETS is bis(ethylene-dithio)tetraselenafulvalene] from rf penetration depth measurements with a tunnel diode oscillator in a pulsed magnetic field. We examined four samples with 1100 field sweeps in a range of angles with the magnetic field parallel and perpendicular to the conducting planes. In the parallel direction, Hc2 appears to include a tricritical point at 1.6 K and 10 T with a phase line that increases to 11 T as the temperature is decreased to 500 mK. The second phase line forms a clearly defined high-field low-temperature region satisfying several of the conditions of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We show remarkably good fits of Hc2 to Werthamer-Helfand-Hohenberg theory in the reentrant α>1, λso=0 regime. We also note a sharp angle dependence of the phase diagram about the field -parallel orientation that characterizes Pauli paramagnetic limiting and further supports the possibility of FFLO behavior. Unrelated to the FFLO study, at fields and temperatures below Hc2 and Tc, we find rich structure in the penetration depth data that we attribute to impurities at the surface altering the superconducting properties while maintaining the same crystallographic axes as Hc2.

Source-reported materials — not catalogue approval

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