Critical Magnetic Fields of Superconducting SnTe

Abstract

Upper critical magnetic fields $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ 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 $H_{c1\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ were also obtained on four of these samples. Values of $P^{*}$ vary from a low of 7.5×${10}^{20}$ per ${\mathrm{cm}}^3$ to a high of 20.0×${10}^{20}$ per ${\mathrm{cm}}^3$. The superconducting transition temperatures $T_0$ increase with increasing $P^{*}$ from a low of 0.034°K to a high of 0.214°K. Values for $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ were obtained from the magnetic field dependence of both ac and dc magnetic susceptibility data. Values for $H_{c1\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ were obtained from measurements of the magnetic moment as a function of magnetic field. The observed values of $H_{c1\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ were rather small, being of the order of ${10}^{-1\mathrm{}}$ 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 $\kappa$. Values of $\kappa$ 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 $T_0\text{'}\mathrm{s}$ and the theoretical predictions of Allen and Cohen is reasonably good.