Probing Trapped Vortices in Superconductors Using Local Microwave Stimulation

Type-II superconductors host DC vortices when subjected to a DC magnetic field surpassing their first critical field. These vortices can be pinned by pinning sites in the superconductor. One possible approach to investigate trapped vortices is to shake them with a local RF magnetic field and analyze the response. Time-dependent Ginzburg-Landau simulations reveal that the wiggle of trapped vortices, induced by a local RF magnetic field [1], typically results in a strong second harmonic response. In our experimental work, we employ a near-field magnetic microwave microscope to stimulate trapped vortices in a local fashion. To create these trapped vortices, a DC magnetic field is applied as the superconductor cools down across its critical temperature, and the measurements are performed after the temperature is below the critical temperature and the DC magnetic field is then turned off. Our experimental results on a Nb sample demonstrate a strong second harmonic response. Furthermore, the correlation between this second harmonic response and the strength of the DC magnetic field is observed.

Reference:

[1] Chung-Yang Wang, Carlota Pereira, Stewart Leith, Guillaume Rosaz, Steven M Anlage, “Microscopic Examination of SRF-quality Nb Films through Local Nonlinear Microwave Response”, arXiv preprint arXiv:2305.07746