Dephasing of conduction electrons by magnetic impurities in $\mathrm{Cu}∕\mathrm{Ni}$ and $\mathrm{Cu}∕\mathrm{Cr}$ samples: Influence of spin-glass transition on the superconducting proximity effect

The dependence of the superconducting proximity effect on the amount of magnetic impurities in the normal part of Andreev interferometers has been studied experimentally. The dephasing rates obtained from fitting experimental data to quasiclassical theory of the proximity effect are consistent with the spin flip scattering from Cr impurities forming a local moment in the Cu host. In contrast, Ni impurities do not form a local moment in Cu and as a result there is no extra dephasing from Ni as long as $\mathrm{Cu}∕\mathrm{Ni}$ alloy remain paramagnetic.

Figure 1

SEM micrograph of a measured sample. Current contacts are labeled $I_1$ and $I_2$; voltage contacts $V_1$ and $V_2$. The area of superconducting loop is $12\mu {\mathrm{m}}^2$.

Figure 2

Magnetoresistance oscillations for two $\mathrm{Cu}∕\mathrm{Ni}$ samples at $T=0.28\mathrm{K}$.

Figure 3

Dots: Reduced amplitude of resistance oscillations in logarithmic scale as a function of impurity concentration at $T=0.28\mathrm{K}$ for $\mathrm{Cu}∕\mathrm{Ni}$ samples. Lines: theoretical fits using $L_{\varphi 0}=1.9\mu \mathrm{m}$ and parameter $a=0$ (solid), 35 (dashed), and 120 (dotted).

Figure 4

Dots: Low-temperature residual resistivity vs Ni impurity concentration. Dashed line: best linear fit.

Figure 5

Circles: Resistivity of $\mathrm{Cu}+4\%\mathrm{Ni}$ sample vs temperature in log scale. Solid line: fit of high-temperature part of resistivity to residual, electron-electron, and electron-phonon contributions. Inset: Kondo contribution to resistivity after subtraction of residual, electron-electron, and electron-phonon contributions. Solid line: best fit to Eq. (2) with ${\rho }_K=0.67\mathrm{n}\Omega \mathrm{cm}$ and $T_K=6.2\mathrm{K}$; dotted line: $T_K=5\mathrm{K}$; dash-dotted line: $T_K=7\mathrm{K}$.

Figure 6

Resistivity of four samples vs temperature in log scale after subtraction of electron-electron and electron-phonon contributions. Dashed line: Fit to Eq. (2) for sample 1, ${\rho }_K=7.0\mathrm{n}\Omega \mathrm{cm}$ and $T_K=9.5\mathrm{K}$.

Figure 7

Dots: Reduced amplitude of resistance oscillations in logarithmic scale as a function of impurity concentration at $T=0.28\mathrm{K}$ for $\mathrm{Cu}∕\mathrm{Cr}$ samples. Lines: theoretical fits using $L_{\varphi 0}=1.6\mu \mathrm{m}$ and parameter $a=0$ (solid), 0.04 (dashed), 0.18 (dotted), and 0.4 (dash-dotted).