Measurements and analysis of the upper critical field $H_{c2}$ on an underdoped and overdoped $L{a}_{2-x}S{r}_{x}Cu{O}_4$ compounds

Abstract

The upper critical field $H_{c2}$ is one of the many non conventional properties of high-$T_c$ cuprates. It is possible that the $H_{c2}(T)$ anomalies are due to the presence of inhomogeneities in the local charge carrier density $\ddot{I}$ of the $Cu{O}_2$ planes. In order to study this point, we have prepared good quality samples of polycrystalline $L{a}_{2-x}S{r}_{x}Cu{O}_4$ using the wet-chemical method, which has demonstrated to produce samples with a better cation distribution. In particular, we have studied the temperature dependence of the second critical field, $H_{c2}(T)$, through the magnetization measurements on two samples with opposite average carrier concentration ($\ddot{I}{}_m=x$) and nearly the same critical temperature, namely $\ddot{I}{}_m=0.08$ (underdoped) and $\ddot{I}{}_m=0.25$ (overdoped). The results close to $T_c$ do not follow the usual Ginzburg-Landau theory and are interpreted by a theory which takes into account the influence of the inhomogeneities.

Published version