Muon-Spin-Rotation Measurements of the Penetration Depth of the Infinite-Layer Electron-Doped ${\mathrm{Sr}}_{0.9}{\mathrm{La}}_{0.1}{\mathrm{CuO}}_2$ Cuprate Superconductor

Muon-spin-rotation ($\mu \mathrm{SR}$) measurements of the in-plane penetration depth ${\lambda }_{ab}$ have been performed in the infinite-layer electron-doped ${\mathrm{Sr}}_{0.9}{\mathrm{La}}_{0.1}{\mathrm{CuO}}_2$ high-$T_c$ superconductor (HTS). Absence of the magnetic rare-earth ions in this compound allowed us to measure for the first time the absolute value of ${\lambda }_{ab}(0)$ in electron-doped HTSs using $\mu \mathrm{SR}$. We found ${\lambda }_{ab}(0)=116(2)\mathrm{nm}$. The zero-temperature depolarization rate $\sigma (0)\propto 1/{\lambda }_{ab}^2(0)=4.6(1)\mu {\mathrm{s}}^{-1}$ is more than 4 times higher than expected from the Uemura line. Therefore, this electron-doped HTS does not follow the Uemura relation found for hole-doped HTSs.

Figure 1

(a) TF-$\mu \mathrm{SR}$ spectra in ${\mathrm{Sr}}_{0.9}{\mathrm{La}}_{0.1}{\mathrm{CuO}}_2$ in a magnetic field of 0.6 T at temperatures $T=50\mathrm{K}$ (above $T_c$) and $T=2.5\mathrm{K}$ (below $T_c$). Solid lines represent fits using Eq. (1). (b) ZF-$\mu \mathrm{SR}$ spectra in ${\mathrm{Sr}}_{0.9}{\mathrm{La}}_{0.1}{\mathrm{CuO}}_2$ at 50 and 2.5 K. Solid lines show fits using an exponential function.

Figure 2

Temperature dependence of the $\mu \mathrm{SR}$ depolarization rate $\sigma (T)$ of ${\mathrm{Sr}}_{0.9}{\mathrm{La}}_{0.1}{\mathrm{CuO}}_2$. Inset: depolarization rate as a function of the external magnetic field $B_{\mathrm{ext}}$ at 10 K.

Figure 3

$T_c$ vs $\sigma (0)$ for $p$- and $n$-type cuprate superconductors. Open symbols represent data taken from Uemura et al. for various $p$-type HTSs [3]. The solid line is the universal Uemura line for different underdoped $p$-type HTSs. Dotted lines represent deviation from the Uemura relation near optimal doping. Solid diamond shows the ${\mathrm{Sr}}_{0.9}{\mathrm{La}}_{0.1}{\mathrm{CuO}}_2$ (SLCO) data obtained in the present work. Solid square and triangle show the data for ${\mathrm{Nd}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4-\delta }$ (NCCO) single crystals obtained from magnetization [20] and optical [21] measurements, respectively. Dashed line represents a tentative $T_c$ vs $\sigma (0)$ relation for $n$-type cuprates.