Enhanced superconductivity at the interface ofW/Sr2RuO4point contacts

Abstract

Differential resistance measurements are conducted for point contacts (PCs) between tungsten tip approaching along the c axis direction and the ab plane of Sr2RuO4 single crystal. Three key features are found. Firstly, within 0.2 mV there is a dome like conductance enhancement due to Andreev reflection at the normal-superconducting interface. By pushing the W tip further, the conductance enhancement increases from 3% to more than 20%, much larger than that was previously reported, probably due to the pressure exerted by the tip. Secondly, there are also superconducting like features at bias higher than 0.2 mV which persists up to 6.2 K, resembling the enhanced superconductivity under uniaxial pressure for bulk Sr2RuO4 crystals but more pronounced here. Third, the logarithmic background can be fitted with the Altshuler-Aronov theory of tunneling into quasi two dimensional electron system, consistent with the highly anisotropic electronic system in Sr2RuO4.The layered perovskite ruthenate Sr 2 RuO 4 (SRO) has shown evidence for spin-triplet, odd-parity superconductivity (SC) which may be useful for topological quantum computation.

Probing chiral superconductivity in Sr2RuO4underneaththe surface by point contact measurements

“…One way to circumvent this problem is to make PCs with hard tips, so the surface layer may be penetrated by the tip [35,36]. Using hard tungsten tips and our home-built point contact setup, we previously obtained a reproducible result for the SC gap (∼0.2 mV) for pure SRO [22], consistent with that estimated by weak coupling theory.…”

“…The resulting SRO-Ru crystal has an extended critical temperature for the superconducting transition (T c ) from the intrinsic 1.5 K to about 3 K, and this enhancement in T c is believed to originate from the interface between Ru inclusions and SRO, possibly due to lattice distortions and strain although the exact mechanism is not confirmed [24,[26][27][28]. In fact, it has been found that uniaxial pressure on pure SRO can enhance SC as well [22,[30][31][32]. Regarding the symmetry of the OP for this enhanced SC, a non-monotonic temperature dependence of the critical current (kinks near 1.5 K) and critical current switchings in so-called topological junctions suggested that the OP symmetry is different from that of pure SRO [33,34].…”

“…Nevertheless, indirect evidence of p-wave superconductivity was reported in local transport measurements, including (scanning) tunnel junction spectroscopy [17][18][19][20] and point contact spectroscopy (PCS) [21,22],…”

Interface between Sr2RuO4 and Ru-metal inclusion: Implications for its superconductivity

“…T c is also found to be enhanced due to dislocations 21 , and in a system where there is an interface of W/Sr 2 RuO 4 point contacts 22 . The unexpected enhancement of T c from 1.5 K to almost 3 K, when micro-sized ruthenium metal inclusions are embedded inside SRO in the eutectic system during crystal growth 23 , is a very interesting and unexplained phenomenon.…”

Josephson effect in a multiorbital model for Sr2RuO4

“…Tunneling spectroscopy experiments also suggest the formation of a dispersive surface Andreev bound state (SABS) at the in-plane edges of SRO [31,33,34]. The dispersive SABSs [35,36] are distinguishable from the dispersionless SABS in a d-wave superconductor.…”