Critical-Field Enhancement and Reduced Dimensionality in Superconducting Layer Compounds

A strong upward curvature in $H_{c2\mathrm{}\parallel }$ and a temperature-dependent critical-field anisotropy are observed in $2H$-Ta${\mathrm{S}}_2$ intercalated with methylamine. This is characteristic of dimensional crossover in Josephson-coupled superconducting layers and is confirmed by a dramatic reduction of the coherence length perpendicular to the layers. Critical fields greater than 213 kG are observed.