Mixed-state transport characteristics of magnesium diboride films

Abstract

We have investigated the low-temperature (T < T c /10) mixed-state current-voltage (IV) response of magnesium diboride films beyond the point where the superconductivity is completely destroyed and the system enters the normal state. The resistance-versus-current R(I) curves are extremely steep and featureless, with a critical current density jc, marking the onset of dissipation, that is unusually high (jc>j d /10) with respect to the depairing current density j d . At large flux densities H c2 /10 B H c2 , the R(I) curve has a functional shape that is largely independent of B, indicating that the rise in resistivity with increasing current occurs mainly due to pair-breaking rather than flux motion. The macroscopic destruction current I * , which drives the system normal, has a [1 − B/H c2 ] flux-density dependence, suggesting that the vortices mainly reduce the effective cross section over which a current of effective density j ∼ j d flows.

Transverse voltage in zero external magnetic fields, its scaling and violation of the time-reversal symmetry in MgB2

“…This dependence is shown there for two different current scales. One can see that the shift of T c is proportional to I 2/3 rather then I 2 , showing that heating is not appreciable and shift is connected with depairing current [4]. Fig.…”