Critical Magnetic Fields of Superconducting SnTe

Abstract

Upper critical magnetic fields ${H}_{c2}(T)$ of five samples of superconducting SnTe possessing different values of the nominal carrier concentration ${P}^{*}$ have been measured as a function of the temperature. Lower critical field data ${H}_{c1}(T)$ were also obtained on four of these samples. Values of ${P}^{*}$ vary from a low of 7.5\ifmmode\times\else\texttimes\fi{}${10}^{20}$ per ${\mathrm{cm}}^{3}$ to a high of 20.0\ifmmode\times\else\texttimes\fi{}${10}^{20}$ per ${\mathrm{cm}}^{3}$. The superconducting transition temperatures ${T}_{0}$ increase with increasing ${P}^{*}$ from a low of 0.034\ifmmode^\circ\else\textdegree\fi{}K to a high of 0.214\ifmmode^\circ\else\textdegree\fi{}K. Values for ${H}_{c2}(T)$ were obtained from the magnetic field dependence of both ac and dc magnetic susceptibility data. Values for ${H}_{c1}(T)$ were obtained from measurements of the magnetic moment as a function of magnetic field. The observed values of ${H}_{c1}(T)$ were rather small, being of the order of ${10}^{\ensuremath{-}1}$ Oe. Application of the Ginsburg-Landau-Abikosov-Gor'kov (GLAG) formulas to the critical magnetic field data allows one to calculate values for the Ginsburg-Landau parameter $\ensuremath{\kappa}$. Values of $\ensuremath{\kappa}$ are found to increase with increasing values of ${P}^{*}$ and range from a low of 3.9 to a high of 6.1. Application of the Goodman-Gor'kov equation to the normal-state parameters of this material lead to values which are about 25% higher than the above values. The agreement between the observed ${T}_{0}'\mathrm{s}$ and the theoretical predictions of Allen and Cohen is reasonably good.