Superconducting Junction of a Single-Crystalline Au Nanowire for an Ideal Josephson Device

Abstract

We report on the fabrication and measurements of a superconducting junction of a single-crystalline Au nanowire, connected to Al electrodes. The current-voltage characteristic curve shows a clear supercurrent branch below the superconducting transition temperature of Al and quantized voltage plateaus on application of microwave radiation, as expected from Josephson relations. Highly transparent (0.95) contacts very close to an ideal limit of 1 are formed at the interface between the normal metal (Au) and the superconductor (Al). The very high transparency is ascribed to the single crystallinity of a Au nanowire and the formation of an oxide-free contact between Au and Al. The subgap structures of the differential conductance are well explained by coherent multiple Andreev reflections (MAR), the hallmark of mesoscopic Josephson junctions. These observations demonstrate that single crystalline Au nanowires can be employed to develop novel quantum devices utilizing coherent electrical transport.

Breakdown of the escape dynamics in Josephson junctions

“…4(a). Hysteresis in I -V curves [10,45,46] does not necessarily indicate canonical Josephson phase dynamics, even in the presence of a Fraunhofer magnetic field pattern [29]. It may rather arise as a result of local heating processes, possibly induced by intrinsic inhomogeneous composition unavoidable for high J c junctions.…”

Fabrication and characterization of PbIn-Au-PbIn superconducting junctions

“…Recent advancement of fabrication methods for nanoscale devices enables us to explore various quantum electronic transport phenomena in nano-hybrid mesoscopic systems combined with superconductivity [2][3][4][5][6][7][8]. Usually aluminum (Al) is used as a superconducting electrode because of its very long superconducting coherence length,  Al ~ 1.6 m.…”

Switching current distributions in InAs nanowire Josephson junctions

“…Scanning electron microscope (SEM) image of a typical NW device is shown in the inset of [19,20]. Since the dissipation power is very low (P Joule ~ 4 pW), the self-heating effect is ruled out to explain the hysteresis.…”

“…After the NWs were transferred to a highly p-doped silicon substrate covered with 250 nm-thick oxide layer, e-beam evaporation of Ti(10 nm)/Al(120 nm) and e-beam lithography were followed to form metallic electrodes. Before metal deposition, the NW surface was deoxidized using buffered hydrofluoric acid for 6 s to ensure transparent contacts.Scanning electron microscope (SEM) image of a typical NW device is shown in the inset of [19,20]. Since the dissipation power is very low (P Joule ~ 4 pW), the self-heating effect is ruled out to explain the hysteresis.…”

“…1a. It is clearly shown that the I-V curves exhibit a hysteretic behavior with a critical current I C , switching from superconducting state to resistive one, and a return current I R (vice versa), while the hysteresis disappears at temperatures higher than T = 0.5 K. The hysteretic I-V curve is attributed to a shunted capacitor formed between source and drain electrodes via the conductive Si substrate [4], Joule heating [18], or an effective capacitance due to a diffusive motion of conduction electrons in the nanostructures [19,20]. Since the dissipation power is very low (P Joule ~ 4 pW), the self-heating effect is ruled out to explain the hysteresis.…”