Shubnikov–de Haas effect in the superconducting state of an organic superconductor

We report the observation of Shubnikov–de Haas (SdH) oscillations in the mixed state of the organic superconductor ${\beta }^{″}-(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}-\mathrm{T}\mathrm{T}\mathrm{F}{)}_2{\mathrm{SF}}_5{\mathrm{CH}}_2{\mathrm{CF}}_2{\mathrm{SO}}_3$ ${(T}_c\approx 4.4$ K). At low temperatures the SdH oscillations persist clearly below the upper critical field $B_{c2\mathrm{}}\mathrm{}\left(0\right)\mathrm{}\approx 3.6$ T almost down to the field where the resistivity vanishes. Rather unusually, no additional damping of the SdH-signal amplitude — as well as of the de Haas–van Alphen amplitude — is observed in the superconducting state. This indicates that the damping in the vortex state of this quasi-two-dimensional superconductor is different in character to that observed for most three-dimensional materials.