A bulk 2D Pauli Limited Superconductor

We present a nearly perfect Pauli-limited critical field phase diagram for the anisotropic organic superconductor \$\alpha$-(ET)$_2$NH$_4$(SCN)$_4$ when the applied magnetic field is oriented parallel to the conducting layers. The critical fields ({H_{c_2}) were found by use of penetration depth measurements. Because {H_{c_2} is Pauli-limited, the size of the superconducting energy gap can be calculated. The role of spin-orbit scattering and many-body effects play a role in explaining our measurements.Comment: 4 pages, 5 figures. V5, corrections were made to the text, present data was include

Comparative magnetotransport and Tc measurements on kappa-(BEDT-TTF)2Cu(SCN)2 under pressure

We compare magnetotransport measurements under pressure on the organic superconductor $\kappa$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$ with different pressure-media and discover that the results are pressure media dependent. This pressure-medium dependence is thought to originate from the difference in thermal contraction between the very soft and highly anisotropic sample and the isotropically contracting, but solid pressure medium, thus resulting in non-hydrostatic pressure on the sample. However, comparison of pressure measurements with different media reveals a pressure-medium independent correlation between the superconducting transition temperature, T$_{\rm c}$, and the size of the quasi 2-dimensional Fermi surface pocket and thus the quasi 2-dimensional carrier density in $\kappa$-(BEDT-TTF)$_{2}$Cu(SCN)$_{2}$. The observed pressure-induced increase in the quasi 2-dimensional carrier density can be interpreted as a transfer of carriers from quasi 1-dimensional Fermi surface sections, reminiscent of a mechanism in cuprate superconductors, where pressure is known to transfer carriers from the insulating charge reservoir layers into the conducting cuprate sheets.Comment: 11 pages, 6 figure