DISSIPATIVE QUANTUM TUNNELING OF DEFECTS IN A MESOSCOPIC METAL

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 epsilon. We clearly observe tunneling rates that increase as the temperature is lowered when kT >> epsilon, 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 alpha, that is defect-specific.