Byong-man Kim

Local modification of the thin YBa2Cu3O7−y microstrips by the voltage-biased atomic force microscope tip

The atomic force microscope (AFM) tip biased at around −15 V is found to be capable of locally modifying the entire thickness of 40-nm-thick semiconducting or superconducting YBa2Cu3O7−y microstrips in air. We show, using combined electrical and AFM measurements, that the local regions underneath the surface of the semiconducting or superconducting YBa2Cu3O7−y microstrips are transformed into either nonconducting or nonsuperconducting regions, respectively, upon applying the negatively biased AFM tip. The conductance of the nonsuperconducting regions is also found to be comparable to that of the superconducting regions before modification at 298 K.

High-Tc edge junctions with a Ga-doped YBa2Cu3O7−δ barrier and interface resistances

High-Tc ramp-edge junctions with a Ga-doped YBa2Cu3O7−δ barrier have been fabricated in the trilayer geometry of YBa2Cu3O7−δ/YBa2Cu2.79Ga0.21O7−δ/YBa2Cu3O7−δ on LaAlO3 single crystals. Interface resistances of the junctions were drastically reduced by using an in situ Ar plasma cleaning treatment. The Ga-doped YBa2Cu3O7−δ junctions with barrier thickness of 200 and 300 A clearly exhibited resistively-shunted-junction-like current–voltage characteristics. The critical currents of the Ga-doped junctions were less sensitive to the variation of the barrier thickness compared to those of the other junctions. The increase of the barrier resistivity by Ga-doping and the in situ rf plasma cleaning treatment resulted in an enhancement of the junction reliability and reproducibility.

Self-radiation and sensing of microwave using a Josephson junction coupled to a frequency-independent antenna

A single Josephson junction (JJ) coupled to a broadband planar antenna was fabricated and its microwave properties were tested at 22 GHz. Sensitivity for the detection of self-radiation power or the reception of microwave power of the JJ coupled to the antenna increased by more than one order of magnitude in comparison to that of the JJ without the antenna. These results demonstrate that the antenna incorporation significantly enhances the convergence of electromagnetic energy between JJ and free space.