[PC6] Vortex, Nickelates

10:00 AM - 10:15 AM JST(1:00 AM - 1:15 AM UTC)

[PC6-02] Imaging of Current-Driven Vortex Formation in YBa₂Cu₃O_7-δ Superconductor

*Shunsuke Nishimura¹, Takeyuki Tsuji^2,3, Takayuki Iwasaki², Mutsuko Hatano², Kento Sasaki¹, Kensuke Kobayashi¹ (1. The University of Tokyo (Japan), 2. Institute of Science Tokyo (Japan), 3. National Institute for Materials Science (Japan))

Keywords:

Quantum Vortex,REBCO,Flux Creep,Vortex Glass,Critical Current

We investigate the most elementary nonequilibrium transition in superconductors: cooling a type-II superconductor while maintaining a transport current. Because vortices impose strong history dependence, the order of temperature and drive is crucial. Unlike the well-known magnetic protocols of zero-field cooling (ZFC) and field cooling (FC), the current-biased analogue, particularly the FC-like process of cooling while a current is applied, has been little explored. Here we report direct visualization of this process using a quantum diamond microscope (QDM). Thin films of the prototypical hard type-II cuprate superconductor YBa₂Cu₃O_7−δ (YBCO) were patterned into microstrips, and we mapped the magnetic-field distribution during cooling under a maintained current. We find that vortices nucleate within the strip and that the number of discrete vortices in the field of view increases linearly with the applied current. When a small offset magnetic field is applied simultaneously, the vortex distribution is skewed opposite to the nominal Lorentz-force direction. Both observations are consistent with a current-induced self-field origin. From the evolution of the magnetic-field distribution as the temperature is lowered until the vortex lines freeze, we further find that across the flow regime into the post-freeze regime, the self-consistent current distribution becomes biased toward the strip center, indicative of glassy dynamics. This behavior is consistent with a steady-state solution in which the magnetic-field profile is time-independent within the flux-creep model. Together, these results show that current history is written into the superconductor as a stable vortex configuration, provide a simple route to studying glass transitions under drive, and motivate a reconsideration of self-field effects intrinsic to dc transport measurements.