Visualization of Current-Driven Vortex Formation in High-$T_c$ Cuprate Superconductors

Abstract

Type-II superconductors exhibit hysteretic behavior due to the presence of quantum vortices, and the order in which temperature and external field are varied plays a decisive role. Here we take current, rather than magnetic field, as the external drive. We image the magnetic field of a high-$T_c$ cuprate superconductor strip after cooling. We confirm that even in zero magnetic field, current-biased cooling nucleates vortices within the strip. With a small external magnetic field, the distribution is polarized opposite to the Lorentz-force direction. These behaviors follow from the self-consistent relation between current and local field in steady flux flow. Our findings show that current history is encoded as vortices. This reveals self-field effects that influence dc measurements and glassy transitions under drive.

Figures (21)

• Figure 1: (a) Schematic of our QDM. (b) Optical micrograph and circuit diagram of the YBCO strip.
• Figure 2: (a) (top) Magnetic-field maps obtained by FC at several $B_{\mathrm{FC}}$. (bottom) Histograms of the vortex $x$-positions. (b) $N^{\mathrm{ROI}}\phi_0/S^{\mathrm{ROI}}$ as a function of $B_{\mathrm{FC}}$ (see text).
• Figure 3: (a) QDM maps after CC-ZF at $T = 71.4~K$ for different currents. (b) QDM maps after CC-$\mathrm{B_a}$ ($B_a=86.4µT$) at $T = 71.4~K$ for different currents. (c) Vortex count versus current for the datasets in (a) and (b). (d) Histograms of the vortex $x$-positions at 1.0 mA and 5.0 mA for (a) and (b). The solid red curves are the distributions of the magnitude of the Ampère self-field, with magnetic flux density rescaled to the vortex occurrence. (e) Current distribution inferred from the CC-ZF (5.0 mA) data (blue), compared with the numerical self-consistent solution (black) [\ref{['eq:self-consistent']}].
• Figure 4: (a) QDM maps obtained at different temperatures during cooling from 93.8K to 69.1K under CC-ZF (top) and CC-$B_a$ ($86.4~µT$, bottom). The arrow at the bottom indicates measurement order. The vortex configuration is unchanged after setting the current to $0~mA$ following the cooldown SI. (b-c) Cross-sectional profiles averaged along the $y$ direction for each map. Traces are taken at every $1~K$, and representative traces are shown in the legend. Panels (b) and (c) correspond to CC-ZF and CC-$B_a$, respectively. The arrows indicate the measurement order.
• Figure 5: (a) Temperature dependence of the resistance at $20~µA$ and $5~mA$. Markers correspond to the panels in \ref{['fig:CC-Tdep']}(a), and the colors of the filled markers match those of the traces in \ref{['fig:CC-Tdep']}(b). (b) Current distributions as a function of $T$ reconstructed from the CC-ZF results in \ref{['fig:CC-Tdep']}(a). The white box indicates the blue band in (a).