Thermally-induced nonlinearities in the surface impedance of superconducting YBCO thin films

Nonlinear microwave properties of HTS thin film coplanar devices

“…The deviation from the field independence at small and large fields can be explained by the effect of magnetization due to the rf field and the overlap of vortices, respectively. Both effects are not accounted for in (4). For mT the calculated total current decreases slightly with decreasing field.…”

“…However, in contrast to their normal-conducting competitors, the power handling capability of superconducting microwave devices is limited by the onset of nonlinear effects in form of a strong increase of the dissipation or intermodulation products at large rf power. Although various physical origins are discussed (e.g., weak links in granular superconductors [2], pair breaking [3], thermal effects [4], magnetic effects [5]), the physical mechanism, that is responsible for the nonlinear surface resistance and that represents a serious restriction for a number of rf applications, is not fully understood. In this paper, we demonstrate that the combination of vortex matter and microwave properties leads to new insight into the nature of the nonlinear microwave properties of superconducting material.…”

Unusual Nonlinear Dynamics Observed in NbN Superconducting Microwave Resonators

“…12), in spite of the short duty cycles that are on the order of ∼ µs, indicates that heating processes which have typical time scale on the order of s to ms [7] are unlikely to cause these effects. Though there are also few who reported a smaller time constant of about 3µs [8] as a result of local heating effects.…”

“…Nonlinear mechanisms in superconductors, which are usually divided into intrinsic and extrinsic origins, include among others, Meissner effect [6], pair-breaking, global and local heating effects [7,8], rf and dc vortex penetration and motion [9], defect points, damaged edges [10], substrate material [11], and weak links [12]. Whereas weak links is a collective term representing various material defects located inside the superconductor such as weak superconducting points switching to normal state under low current density, Josephson junctions forming inside the superconductor structure, grainboundaries, voids, insulating oxides, insulating planes.…”

Joule heating and high frequency nonlinear effects in the surface impedance of high Tc superconductors

“…44 Wosik et al insist on the importance of thermal effects as the root of the nonlinear behavior. 45,46,47 They have used the pulsed measurement method, which, in principle, prevents or at least reduces heating of the films. These experiments were repeated using thermally isolated films as well as films that are thermally connected through the substrate with the heat sink cooled at 20 K. The authors 45,46,47 have shown that the temperature increase of an isolated sample can reach 30 K. For the case of a film thermally connected to the heat sink the temperature rise will be of only 2.5 K.…”