Figure 4. Transition temperature as a function of magnetic field.

(a) Temperature dependence of ZFC dc susceptibility χ at different H applied parallel to the surface (ab plane). For clarity, only data for Cs-intercalated BP are shown. (b) Parallel and perpendicular critical fields as a function of temperature for all M_xP compounds in this study. Error bars indicate the accuracy of determination of the critical temperature from χ(T) curves such as those shown in a (open symbols) and of the critical field from m′(H) (solid symbols). Solid curves are fits to the BCS expression H_c∝1−(T/T_c)².