Description:

Abstract: The upper critical magnetic field, H_c2, the nucleation field of surface superconductivity, H_c3, and the thermodynamic critical magnetic field, H_c, were evaluated within the weak-coupling Eilenberger formalism with arbitrary scattering [1-3]. We find that the maximum ratio, R = H_c3 / H_c2, reached for a magnetic field parallel to the surface remains within 1.55 <= R(T) <= 2.34, regardless of temperature or scattering. Surprisingly, magnetic scattering has a milder impact on R(T) than the nonmagnetic scattering. The surface superconductivity is quite robust: the maximum ratio R ~= 1.7 is found even in the superconducting gapless state.

Similar calculations were conducted for thin films, thinner than the coherence length. There we find a substantial enhancement of the transition temperature T_c by a magnetic field parallel to the film surface. We also find field-induced re-entrant superconductivity.

Finally, by conducting high precision high-resolution calculations of the free energy, F_c, as a function of the pair-breaking scattering at very low temperatures, we confirm the existence of a type-2 1/2 topological quantum phase transition from gapped to gapless superconducting state suggested recently from the discontinuity of the third derivative of F_c from the analytical Maki’s solutions at T = 0 [4]. Here we show the full temperature dependence of the third derivative and the temperature broadening of this quantum critical point to a cone-like structure as observed for other quantum critical phase transitions.

Speaker: Ruslan Prozorov, Senior Physicist, Ames National Laboratory

Host: Venkat Chandrasekhar