Local Nonlinear Microwave Dynamics of Pinned and Semi-Loop Vortices
Author: Anlage, Steven
Affiliation: University of Maryland
Type: Contributed Talk
Session: Superconducting and hybrid devices
Date and Time: 23.07.2026, 10:55 - 11:15
Trapped vortices in superconductors disrupt the operation of superconducting quantum and digital electronic circuits and introduce residual loss in SRF cavities. Understanding the detailed dynamics of trapped vortices under oscillating magnetic fields is essential for advancing these technologies. We have developed a near-field magnetic microwave microscope to study the dynamics of a limited number of trapped vortices under the probe when stimulated by a localized rf magnetic field. We observe third-harmonic (P_3f) generation from probe-induced RF vortex semi-loops created at surface defects in Nb and Nb_3Sn. In addition, by measuring the local second-harmonic response (P_2f) at sub-femto-Watt levels, we isolate signals exclusively arising from trapped persistent vortices, excluding contributions from surface defects and screening currents. Models of Nb superconductor hosting vortex pinning sites are introduced and studied with Time-Dependent Ginzburg-Landau simulations of probe/sample interaction to better understand the measured second- and third-harmonic response. The simulation results demonstrate that the second-harmonic response of trapped vortex motion under a localized rf magnetic field shares key features with the experimental data. This measurement technique provides access to few-vortex dynamics at the micron scale, such as depinning events and spatially-resolved pinning properties, as demonstrated in measurements on a Nb film with an antidot flux pinning array.