Unusual temperature dependence of the London penetration depth in all-organic β``-(ET)_2SF_5CH_2CF_2SO_3 single crystals

Abstract

The temperature dependence of the in-plane, λ_{\parallel}, and interplane, λ_{\perp}, London penetration depth was measured in the metal-free all-organic superconductor β-ET (see title) ($T_c\approx$ 5.2 K). λ_{\parallel} ~T^3 up to 0.5 Tc, a power law previously observed only in materials thought to be p-wave superconductors. λ_{\perp} is larger than the sample dimensions down to the lowest temperatures (0.35 K), implying an anisotropy of λ_{\perp}/λ_{\parallel} ~ 400-800.

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