Kondo effect in underdoped<i>n</i>-type superconductors

Abstract

We present high-field magnetotransport properties of high-quality single-crystalline thin films of heavily underdoped nonsuperconducting $(\mathrm{L}\mathrm{a},\mathrm{C}\mathrm{e}{)}_{2}{\mathrm{CuO}}_{4},$ $(\mathrm{P}\mathrm{r},\mathrm{C}\mathrm{e}{)}_{2}{\mathrm{CuO}}_{4},$ and $(\mathrm{N}\mathrm{d},\mathrm{C}\mathrm{e}{)}_{2}{\mathrm{CuO}}_{4}.$ All three materials show identical behavior. They are metallic at high temperatures and show an insulating ``upturn'' at low temperatures. The insulating upturn has a $\mathrm{log}T$ dependence, but saturates toward the lowest temperatures. Notably, the insulating upturn tends to be suppressed by applying magnetic fields. This negative magnetoresistance has a $\mathrm{log}B$ dependence, and its anisotropy shows a nonsimple behavior. We discuss these findings from the viewpoints of Kondo scattering and also two-dimensional weak localization, and demonstrate Kondo scattering as a more plausible explanation. The Kondo scatters are identified as ${\mathrm{Cu}}^{2+}$ spins in the ${\mathrm{CuO}}_{2}$ planes.