Origin of the Anomalous Low Temperature Upturn in the Resistivity of the Electron-Doped Cuprate Superconductors

The temperature, doping, and field dependences of the magnetoresistance (MR) in ${\mathrm{Pr}}_{2-x}{\mathrm{C}\mathrm{e}}_x{\mathrm{C}\mathrm{u}\mathrm{O}}_{4-\delta }$ films are reported. We distinguish between orbital MR, found when the magnetic field is applied perpendicular to the $ab$ planes, and the nearly isotropic spin MR. The latter, the major MR effect in the superconducting samples, appears in the region of the doping-temperature phase diagram where $d\rho /dT<0$, or an upturn in the resistivity appears. We conclude that the upturn originates from spin scattering processes.

Figure 1

The $ab$-plane resistivity of ${\mathrm{Pr}}_{2-x}{\mathrm{C}\mathrm{e}}_x{\mathrm{C}\mathrm{u}\mathrm{O}}_{4-\delta }$ films vs magnetic field applied perpendicular to the $ab$ plane ($H\perp ab$).

Figure 2

The $x=0.11$ sample at $T=1.8\mathrm{K}$. (a) The resistivity vs field at $\theta =0$ ($H\parallel ab$). Solid line is a linear fit to the high fields region. (b) Calculation of the angular dependence of a spin effect; see text for details.

Figure 3

(a) The temperature dependence of the LMR ($H\parallel ab$) for the $x=0.13$ sample at various temperatures. Note that the MR turns positive above 80 K. (b) The resistivity as a function of temperature for the same sample (solid line, left hand scale). The effective exponent $d\ln (\rho -{\rho }_0)/d\ln T$ (circles, right hand scale) changes rapidly around 90 K, i.e., where the LMR changes sign. The dashed line is a guide to the eye.

Figure 4

Comparison between field sweeps $H\perp ab$ (green squares) and rotation in a magnetic field of 32.4 T (black circles) for various dopings at 1.5 K. The difference between the two measurements is due to the spin effect, which vanishes for $x\ge 0.16$ (see text).

Figure 5

The difference in resistivity between the field sweep and the rotation in field at 30° taken from Fig. 4 and normalized with the resistivity at 32.4 T ($H\perp ab$).