New aspects of microwave properties of Nb in the mixed state

• Published in: Physica. C, Superconductivity Vol. 470; no. 19; pp. 901 - 903
• Main Authors: Pompeo, N., Silva, E., Sarti, S., Attanasio, C., Cirillo, C.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01-10-2010; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Corbino disk; Creep (materials); Deviation; Dynamic tests; Exact sciences and technology; Fluid flow; Mesoscopic and nanoscale systems; Microwaves; Niobium; Physics; Properties of type I and type II superconductors; Superconducting films and low-dimensional structures; Superconducting materials (excluding high-tc compounds); Superconductivity; Surface impedance; Vortex dynamics; Vortex lattices ,flux pinning, flux creep; Vortices; Surface impedance; Vortex dynamics; Nb; Corbino disk; Superconducting thin films; Frequency dependence; Flux line; Fluxons; Mixed state; Flux creep; Nanostructures; Switching; Niobium; Microwave conductivity; Transition elements; Vortices; High field; Instability
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2010.02.063

We present a study of the frequency dependence of the vortex dynamics in a conventional superconductor. We have employed a swept frequency, Corbino disk technique to investigate the temperature (
3.6
K
–
T
c
) and high-field (from
H
c
2
/
2
to
H
c
2
) microwave complex resistivity in Nb thin (20–40
nm) films as a function of the frequency (1–20
GHz). We have found several previously unnoticed features: (i) a field-dependent depinning frequency in the GHz range; (ii) deviations from the accepted frequency dependence
[1], that can be ascribed to some kind of vortex creep; and (iii) the presence of switching phenomena, reminiscent of vortex instabilities. We discuss the possible origin of the features here reported.