Vortex dynamics in organic superconductors

The plasticity of vortex crystals, their melting at the line Tm(B) or the corresponding freezing of the vortex liquid are on agenda in current studies of layered superconductors. We review the NMR experiments and present a related theory which prove an unexpectedly large concentration of highly diffusive thermally activated defects: interstitials and vacancies below Tm and indicate a presence of unbound 2D dislocations above Tm. Also we interpret the critical 2D regime of freezing above Tm. The picture is based on the analysis of the longitudinal relaxation rate W(T, B) of the 1H NMR in the layered organic superconductor κ-BEDT with respect to a developed theory of the NMR relaxation by defects and critical fluctuations. The high magnitude of the peak in W at Tm, its sharpening at lower fields B ~ 1Tsl and especially the ≪master curve ≫ structure in the family of lines W(T, B = const) at the low T slope of the peak lead to above conclusions.