Unconventional superconductivity at mesoscopic point contacts on the 3D Dirac semimetal Cd3As2

A superconducting phase at nanometre-scale interfaces between a pure silver mesoscopic point contact and the 3D Dirac semimetal Cd 3 As 2 is observed. Three-dimensional (3D) Dirac semimetals 1 , 2 , 3 exist close to topological phase boundaries 4 which, in principle, should make it possible to drive them into exotic new phases, such as topological superconductivity 5 , by breaking certain symmetries. A practical realization of this idea has, however, hitherto been lacking. Here we show that the mesoscopic point contacts between pure silver (Ag) and the 3D Dirac semimetal Cd 3 As 2 (ref. 2 ) exhibit unconventional superconductivity 6 with a critical temperature (onset) greater than 6 K whereas neither Cd 3 As 2 nor Ag are superconductors. A gap amplitude of 6.5 meV is measured spectroscopically in this phase that varies weakly with temperature and survives up to a remarkably high temperature of 13 K, indicating the presence of a robust normal-state pseudogap 7 . The observations indicate the emergence of a new unconventional superconducting phase that exists in a quantum mechanically confined region under a point contact between a Dirac semimetal and a normal metal.