Dissipative quantum tunneling of a single defect in Bi.

Abstract

We have studied the dynamics of single bistable defects in submicrometer Bi wires at temperatures 0.1--2 K. The defect motions cause measurable changes in the sample resistance via universal conductance fluctuations. The temperature dependence of the transition rates agrees quantitatively with the predictions of dissipative quantum tunneling theory, which describes tunneling of a defect in a double-well potential with strong dissipation from the electron bath. We report detailed measurements of a single defect as a function of magnetic field, and discuss the field dependence of the defect-potential asymmetry \ensuremath{\varepsilon}, the defect-bath coupling constant \ensuremath{\alpha}, and the renormalized tunneling matrix element ${\mathrm{\ensuremath{\Delta}}}_{\mathit{r}}$.