Interpretation of enhanced plasticity in superconducting tantalum in termsof enhanced quantum tunneling of dislocation through the Peierls potential

The super-normal effect of the flow stress, i.e. a reversible increase of t he flow stress accompanying the transition from the superconducting to the normal state by application of a magnetic field, observed in ultra-high pur ity tantalum single crystals has been analyzed according to the recent theo ry by Petukhov et al. on dissipative dislocation tunneling [Philos. Mag. A 73 (1998) 1041]. Experimentally obtained temperature dependence of the supe r-normal effect and that of the strain rate sensitivity of the flow stress can well be fitted by the theory. Electronic viscosity coefficient of the d islocation motion in the normal state obtained in this fitting is 0.016 N.s /m(2) According to this analysis, the super-normal effect in tantalum is du e to the change of the rate of tunneling through the Peierls potential acco mpanying the change of electron viscosity by the super-normal transition.