Unusual temperature dependence of the London penetration depth in all-organic β ″ − ( ET ) 2 SF 5 CH 2 CF 2 SO 3 single crystals

The temperature dependence of the in-plane, {lambda}{sub {parallel}}(T), and interplane, {lambda}{sub {perpendicular}}(T), London penetration depth was measured in the metal-free all-organic superconductor {beta}''-(ET){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} (T{sub c}{approx}5.2 K). {Delta}{lambda}{sub ||}(T){proportional_to}T{sup 3} up to 0.5 T{sub c}, a power law previously observed only in materials thought to be p-wave superconductors. {lambda}{sub {perpendicular}} is larger than the sample dimensions down to the lowest temperatures (0.35 K), implying an anisotropy of {lambda}{sub {perpendicular}}/{lambda}{sub {parallel}}{approx}400-800.