Pinning properties of FeSeTe thin film through multifrequency measurements of the surface impedance

Abstract

We present high frequency measurements of the vortex dynamics of a FeSe x Te 1−x (x = 0.5) thin film grown on a CaF 2 substrate and with a critical temperature T c ≃ 18 K, performed by means of a dual frequency dielectric resonator at 16.4 GHz and 26.6 GHz. We extract and discuss various important vortex parameters related to the pinning properties of the sample, such as the characteristic frequency ν c , the pinning constant k p and the pinning barrier height U relevant for creep phenomena. We find that the vortex system is in the single-vortex regime, and that pinning attains relatively high values in terms of k p , indicating significant pinning at the high frequencies here studied. The pinning barrier energy U is quite small and exhibits a non-monotonous temperature dependence with a maximum near 12 K. This result is discussed in terms of core pinning of small portion of vortices of size ∝ ξ 3 jumping out of the pinning wells over very small distances, a process which is favoured in the high frequency, short ranged vortex oscillations here explored.

Microwave measurements of the high magnetic field vortex motion pinning parameters in Nb$_3$Sn

“…It must be noticed that the peak in U 0,min is narrower than what expected from the theory and also that the lower temperature U 0,min dependence does not saturate to a finite value but it is a linear function of T . The narrow peak and the increase of U 0 with the temperature was already observed in other superconductors [68,[70][71][72]. This discrepancy with respect to the theory was justified introducing pinning models that included junctions and non-homogeneities [70,[73][74][75][76].…”

“…Considering other superconducting materials, it comes out that the obtained values at 4 T are comparable with those measured in a MgB 2 thin film in the same H-T region [66]). On the other hand, it must be noticed that FeSe 0.5 Te 0.5 and YBa 2 Cu 3 O 7-δ performances are still far, in fact at 12 K and 0.6 T ν p ∼ 22 GHz and > 40 GHz, respectively in 300 nm and 240 nm thick FeSe 0.5 Te 0.5 films [67,68] while ν p ∼ 50 GHz in 100 nm thick YBa 2 Cu 3 O 7-δ films at 72 K [60]. For a more complete comparison, thin Nb 3 Sn films should be characterized in the same conditions to experimentally verify the increase of ν p with the reduction of the sample thickness.…”