Zero-crossing Shapiro steps in focused-ion-beam-tailored high-$T_c$ superconducting microstructures

Understand

Microwave response of S-shaped Bi$_2$Sr$_2$CaCu2O$_{8+x}$ (Bi-2212) micron-scale samples, in which the supercurrent was forced to flow perpendicular to the crystal layers, was investigated.

• A treatment with a focused ion beam allowed us to reduce the plasma frequency down to $f_p$$\sim$5 GHz at $T$=0.3 K in naturally stacked Josephson junctions in a crystal.
• We observed Shapiro steps at frequencies as low as $\sim$5 GHz.
• Well-developed zero-crossing Shapiro steps were observed at frequencies as low as $\sim$10 GHz.