Mesoscopic superconductivity and high spin polarization coexisting at metallic point contacts on Weyl semimetal TaAs

Abstract

A Weyl semimetal is a topologically non-trivial phase of matter that hosts mass-less Weyl fermions, the particles that remained elusive for more than 80 years since their theoretical discovery. The Weyl semimetals exhibit unique transport properties and remarkably high surface spin polarization. Here we show that a mesoscopic superconducting phase with critical temperature Tc=7 K can be realized by forming metallic point contacts with silver (Ag) on single crystals of TaAs, while neither Ag nor TaAs are superconductors. Andreev reflection spectroscopy of such point contacts reveals a superconducting gap of 1.2 meV that coexists with a high transport spin polarization of 60% indicating a highly spin-polarized supercurrent flowing through the point contacts on TaAs. Therefore, apart from the discovery of a novel mesoscopic superconducting phase, our results also show that the point contacts on Weyl semimetals are potentially important for applications in spintronics.

Chirality blockade of Andreev reflection in a magnetic Weyl semimetal

“…We also discuss the subtle role played by inversion symmetry by contrasting a scalar with a pseudoscalar pair potential [10]. The absence of the chirality blockade for pseudoscalar pairing explains why it did not appear in the many previous studies of Andreev reflection in a Weyl semimetal [11][12][13][14][15][16][17][18][19].…”

Superconductivity induced at a point contact on the topological semimetal tungsten carbide

“…Recently, superconductivity was induced at a point contact between a normal metal tip and the 3D Dirac semimetal Cd 3 As 2 [5,6]. Soon after, similar phenomenon was reproduced in the Weyl semimetal TaAs [7,8]. In particular, the induced superconductivity could coexist with preserved topological properties in the line-nodal semimetal ZrSiS [9].…”

“…Meanwhile, unconventional superconductivity has been proposed for Cd 3 As 2 , yet based on two distinct experimental observations, i.e., a pseudogap behavior above the critical temperature [5] or an abnormal spectral shape at low temperatures [6]. For TaAs, such unconventionality is still in debate [7,8]. Therefore, more evidences are desired to clarify this issue.Most recently, a new type of topological quasiparticles was proposed for the metals hosting symmetry-protected three-band crossings (three-fold degeneracy) near the Fermi level [11][12][13].…”

“…Such tip-induced superconductivity (TISC) is very exciting since it is extremely rare in common metals and provides a unique way of searching topological superconductivity [10]. Although the most likely origins of the TISC were speculated to be tip pressureinduced band reconstruction, confinement effect, charge carrier doping [7], or remarkable enhancement of density of states under the tip [9], the dominant mechanism remains elusive. Meanwhile, unconventional superconductivity has been proposed for Cd 3 As 2 , yet based on two distinct experimental observations, i.e., a pseudogap behavior above the critical temperature [5] or an abnormal spectral shape at low temperatures [6].…”

“…The TISC on WC in addition to Cd 3 As 2 [5,6] and TaAs [7,8] implies a common mechanism shared by these topological semimetals. Among several possible explanations, the first candidate is band structure modifications induced by tip pressure as proposed in previous studies.…”