Pressure Dependence Transport Studies of the Possible Charge Kondo Effect in Tl-doped PbTe

Pb$_{1-x}$Tl$_x$Te is noteworthy for a high superconducting transition temperature relative to carrier concentration, as well as normal state properties consistent with a charge-Kondo effect. Recent experiments also demonstrate that the onset of an observable superconducting T$_c$ with Tl concentration at x$\sim$0.3\% coincides with features characteristic of charge Kondo [1], including d$\rho$/dT$<$0 at low temperatures and an unusual linear variation of the resistivity $\rho(T)$=$\rho_0 $+AT at higher temperatures. Together, these observations are consistent with an association between the two phenomena [2]. We report the effect of applied pressures up to P$\sim1.5$GPa on $\rho(T)$, T$_c$, and the Hall number p$_H\equiv$R$_H^{-1}$ for x= 0.3\%, 0.8\%, and 1.3\%. T$_c$ is reduced sharply with pressure, dT$_c$/dP=400-500mK/GPa as the low temperature Kondo- like upturn in $\rho(T)$ is weakened. Also, dA/dP$<$0 and dp$_H$/dP$>$0. These observations are discussed in the context of the proposed charge-Kondo model for Pb$_{1-x}$Tl$_x$Te. [1] Y. Matsushita, H. Bluhm, T.H. Geballe and I.R. Fisher, Phys.Rev.Lett. 94, 157002(2005).[2] M. Dzero and J. Schmalian, Phys.Rev.Lett. 94, 157003 (2005). This work is supported by NSF frant DMR-0520552.