AC conductivity of a niobium single crystal in a swept magnetic field

作者：Tsindlekht M I^*; Genkin V M; Leviev G I; Schlussel Y; Tulin V A; Berezin V A

来源：Physica C-Superconductivity and Its Applications, 2012, 473: 6-10.

DOI：10.1016/j.physc.2011.11.005

• Surface superconductivity
• Swept field
• AC susceptibility

We report results of experimental studies of the ac susceptibility of a Nb single crystal at low frequencies in swept magnetic fields applied parallel to the surface. Analysis of the experimental data shows that the swept magnetic field significantly changes the bulk conductivity for H-c1 < H-0 < H-c2. It becomes dissipative with substantial frequency dispersion. At the surface, a layer with enhanced conductivity in comparison to the bulk was detected for H-c1 < H-0 < H-c2. This layer provides a considerable contribution to the shielding and absorption of the ac field even in the mixed state. There is anomaly of an ac susceptibility in the field near the transition between Abrikosov's phase and surface superconducting states. Conductivity of the surface layer in large dc fields H-c2 < H-0 < H-c3, measured in point-by-point mode, and in a swept field is unexpectedly small in spite of the large value of the order parameter near the surface. We demonstrate that the swept magnetic field affects the ac response of the surface superconducting states.

• 出版日期2012-2