Tunnel junctions formed between tungsten wires display very large zero-bias conductance peaks characteristic of Kondo-type magnetic scattering of tunneling electrons. No electron correlation effects are seen despite the fact that the system appears to be below the Kondo temperature. Time-dependent changes in the tunnel conductance are identified with the scattering behavior of a single local magnetic moment. This behavior can be switched reversibly by adjusting the stress in the junction.

• Received 20 September 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.2070