Anisotropic interfacial superconductivity induced at point contacts on topological semimetal grey arsenic

The origin of superconductivity observed at the point contact between the normal metal tip and the topological material remains uncertain due to the potential presence of superconducting elements or allotropes impurities. It is imperative to seek out a topological material entirely free of superconducting impurities and induce superconductivity between it and normal tips to verify the source of the induced superconductivity. Here, we report the observation of superconductivity up to 9 K induced at point contacts between normal metal tips and the topological material grey arsenic, which is free of superconductivity. The determined temperature dependencies of superconducting gaps Δ( T ) deviate from the Bardeen-Cooper-Schrieffer (BCS) superconductivity law, exhibiting abnormal behavior. Furthermore, the highly anisotropic upper critical field H c2 ( T ) suggests the anisotropy of the projected interfacial Fermi surface. By tuning the junction resistance, we obtained a negative correlation between the superconducting gap A and the effective barrier height Z , which validates the interfacial coupling strength as a key factor in the observed tip-induced superconductivity. These experimental results provide guidance for the relevant theory about tip-induced superconductivity on topological materials.