Thermal modelization and experiments on the current of superconducting microbridges dependence to light in the 10-90K range
Résumé
We have previously reported (Applied Superconductivity Conference 1992) that the critical current I c dependence versus optical power P in the mW range at 780 nm, with P focused on microbridges of YBCO thin films, could be calculated using simple calculations on heat production in the superconducting film and heat conduction to the substrate. The model was valid only on a limited range of temperature T where the thermal boundary resistance Rbd lying at the film-substrate interface could be taken as a constant R o = 10 -3 Kcm2/W. We present a full model obtained by integration of the coupled Fourier equations giving the temperature dependence in the superconducting anisotropic YBCO film and in its substrate. We show that the thermal boundary resistance modelized as Rtx I (T) = B/T3+Ro, with B/T 3 given by the acoustic mismath model, is still limiting the heat transfer from the film to the substrate at least down to 10K. As a consequence, a simple model that only uses Rbd(T) and dlc/dT is derived which allows realistic evaluations of the current sensitivity SI(P,T ) to the applied power P over the 10-90K temperature range Calculated SI(P,T ) which lies in the 0.1-1 A/W range agrees well with those measured on YBCO/MgO or YBCO/SrTiO 3 devices.
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