High-Supercurrent-Density Contacts and Josephson Effect of Strontium Ruthenate

Abstract

We have developed a process of fabricating high-supercurrent-density contacts to Sr2RuO4 as a key technology for the development of topological quantum computing. To minimize degradation, the niobium contacts were formed on crushed surfaces of Sr2RuO4 crystals by an in situ process. A critical supercurrent density as high as 107 A/m2 was achieved, a value two to three orders of magnitude greater than those reported previously. However, the unexpectedly small magnitude of the product of the critical current and the normal resistance indicates the existence of a fundamental limitation arising from Josephson coupling between spin-singlet and spin-triplet superconductivities.

Spontaneous edge current in a small chiral superconductor with a rough surface

“…The edge current is mainly carried by five combinations: j 01 , j 12 , j 21 , j 23 , and j 32 . The four components j 12 , j 21 , j 23 , and j 32 almost cancel one another. As shown in Fig.…”

“…6(b), we decompose the current into the series of j ab , where we show only dominant components of j 21 , j 23 , and j 01 . We note that j 12 23 , j 12 , and j 32 . As shown in Fig.…”

“…Experimentally it is difficult to make a superconducting sample with a specular surface. For instance, a small ruthenate superconductor cluster can be fabricated by using the focused ion beam technique [23,24], which would seriously damage the sample quality near the surface. Several theoretical papers have already suggested the presence of edge states in a chiral p-wave superconductor when there is surface roughness [25,26].…”

Inversion symmetry of Josephson current as test of chiral domain wall motion inSr2RuO4

“…3(b). The reduction of the peak width from the expected value (H/H 0 ∼0.15) is attributed to the concentration of the applied magnetic field at the edge of the SRO crystal due to the Meissner effect [28]. As further reducing the junction width to w = 5.8 µm, the I c (H) became rather conventinal as shown in Fig.…”

“…We speculate that the relatively larger domain can be induced by s-wave Nb films whose superconducting transition temperature T c (∼6.5 K) is higher than that of SRO. In our Josephson junctions, the contact between the Nb films and SRO realizes a high current density [28] compared to that of other junctions using the 1.5-K phase. Thus, the phase of SRO was locked to that of the Nb film through the Josephson coupling, which probably results in the creation of the relatively large size of domains.…”