Dissipative quantum tunneling of defects in a mesoscopic metal

Abstract

We have studied the dynamics of single bistable defects in sub-micron Bi wires at temperatures 0.1–2 K. The defect motions can cause large changes in the sample resistance via universal conductance fluctuations. The dynamics are due to the defect particle, coupled to the electron bath, tunneling in a double-well potential with asymmetry ɛ. We clearly observe tunneling rates that increase as the temperature is lowered when kT≫ɛ, as predicted by the theory of dissipative quantum tunneling. Fits of the theory to the data yield a value of the defect-electron bath coupling constant α, that is defect-specific.