RF-studies of vortex dynamics in isotropic type-II superconductors

Abstract

We have measured the surface impedance of thick superconductors in the mixed state over a broad 2 kHz -20 MHz frequency range. The depinning cross-over is observed; but it is much broader than expected from classical theories of pinning. A striking result is the existence of size effects which invalidate the common interpretation of the low-frequency surface inductance in terms of a single penetration depth. Instead, a two-mode description of vortex dynamics, assuming free vortex flow in the bulk and surface pinning, accounts quantitatively for the spectrum of the complex apparent penetration depth.

Microwave surface transport in narrow-bandgap PdSe2 -MOSFETs

“…For ideal carrier injection in the channel, the admittance spectrum reflects a crossover from an elastance (1/C G ) dominated regime at low frequency to a lattice-friction dominated regime at high frequency. Such an RF crossover from elastic-dominated to friction-dominated response is quite general and has been previously reported in the context of vortex matter dynamics in superconductors [35][36][37]. In atomically thin 2D materials, screening is negligible and one can readily extract from C G the quantum compressibility contribution C Q = e 2 DOS in series with the geometrical capacitance C geo .…”

Reliable determination of vortex parameters from measurements of the microwave complex resistivity

“…where ω p,ef f,T M = k p /η + 2ε l Φ 0 /(lηd) = ω p + ω ps is an overall pinning frequency combining the effects of bulk pinning (ω p ) and surface pinning (ω ps ), d is the thickness of the thin film, ε l is a (field dependent) fluxon line energy, 21 and l is a characteristic length describing the surface pinning. 14 When surface pinning is negligible, l → ∞. Equation ( 7) coincides with the GR expression, Eq.…”

“…As a consequence, the response of the vortex system can attain very complex frequency dependencies even in the linear regime of small currents. 9,10,11,12,13,14 In those cases, it is rather difficult to reliably determine (or even define) the vortex parameters.…”

Wideband microwave measurements in Nb/Pd84Ni16/Nb structures and comparison with thin Nb films

“…The appearance of a Hall term in (1) can be neglected in superconductors in the dirty limit. From the basic equation of motion (1), many models can be derived, differing essentially for the impact of thermal effects and elasticity of the vortex lattice [15,30,34,35]. Nevertheless, it has been shown [36] that the seemingly large variety of models yield expressions for the vortex resistivity ρ vm that can be cast in a single, very general expression:…”