Investigation of DC current injection effect on the microwave characteristics of HTS YBCO microstrip resonators

• Current (spin) injection effect in LSMO/YBCO was studied by impedance measurements.
• Complex impedance of YBCO increases at current injection from LSMO to YBCO at 77 K.
• This increase is due to an increase of the quasiparticle conductivity of YBCO.
• Injection does not significantly affect the relaxation time of the quasiparticles.

The DC current injection effect from a ferromagnetic (FM) La0.7Sr0.3MnO3 (LSMO) to a high temperature superconducting (HTS) Y1Ba2Cu3O7−x (YBCO) thin film was investigated by the microwave surface impedance measurements in a FM/HTS structure, formed as a microstrip resonator for improving the sensitivity of the experiments. The quality factor and the resonance frequency of this structure were found to strongly depend on the current strength, injected from the LSMO electrode into the HTS microstrip electrode. The magnetic penetration depth and the quasiparticle conductivity of the HTS component were determined to increase under DC current injection process, which in all probability stimulated breaking of Cooper pairs and led to a decrease of the superfluid concentration and an increase of the normal fluid concentration without significantly affecting the relaxation time of the quasiparticles.