Properties that change as superconductivity disappears at high-doping concentrations in La2−xSrxCuO4

Abstract

In the system ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_4$, as x and p (the [${\mathrm{CuO}}_2$ ${]}^{\mathrm{p}\mathrm{-}2}$ charge) are increased, the superconducting transition temperature first increases, then peaks becoming nonsuperconducting for x≳0.26. We report here a search for changes in physical properties at the values of x where $T_c$ is observed to change its behavior. The in-plane lattice constants and the normal resistivity both show a continued monotonic decrease over this entire region, suggesting that no major electronic changes occur. The tetragonal-to-orthorhombic transition temperature $T_s$ also decreases with increasing x and becomes unobservable for x≳0.19, suggesting that this structural transition itself is unrelated to the disappearance of superconductivity that occurs at higher doping levels. The magnetic spin susceptibility ${\chi }_{\mathrm{spin}(\mathrm{T}}$) generally rises gradually with increasing doping (reflecting decreasing spin-spin interactions), reaches a maximum near x∼0.25, and then decreases. There is a weak peak in ${\chi }_{\mathrm{spin}(\mathrm{T}}$) as a function of temperature at T=$T_{\max }$. As a function of increasing x,$T_{\max }$ falls to zero near x∼0.25. These two observations might be related to the disappearance of superconductivity, since all three occur near the same value of Sr content x.