Anomalous low-temperature resistivity of metallic trilayers: Possible evidence for electron scattering on symmetrical two-level systems

Abstract

We report on a study of the ground state of $\mathrm{Co}/M/\mathrm{Co}$ $(M$ is a nonmagnetic metallic spacer) metallic trilayers where electrical resistivity increases logarithmically with decreasing temperature $(\ensuremath{\Delta}\ensuremath{\rho}\ensuremath{\sim}A\mathrm{log}T)$ down to about 100 mK due to two-dimensional electron-electron interactions. At lower temperatures the crossover from a logarithmic to an anomalous non-Fermi-liquid behavior $(\ensuremath{\Delta}\ensuremath{\rho}\ensuremath{\sim}\ensuremath{\beta}\sqrt{T})$ is observed, with $\ensuremath{\beta}$ independent of the magnetic field up to 13 T. The $\sqrt{T}$ dependence of the resistivity is interpreted as due to scattering of the electrons by symmetrical two-level tunneling systems.