Large superconducting double-gap, a pronounced pseudogap and evidence for proximity-induced topological superconductivity in the Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$/Fe$_{\mathrm{1+y}}$Te interfacial superconductor*

We investigate directional point-contact spectroscopy on a Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$/ Fe$_{\mathrm{1+y}}$Te heterostructure, fabricated via van der Waals epitaxy, which is interfacial superconducting with an onset T$_{\mathrm{C}}$ at 12K and zero resistance below 8K. A large superconducting twin-gap structure is seen down to 0.27K, together with a zero bias conductance peak. The anisotropic smaller gap ($\Delta _{\mathrm{1}}$) is around 5 meV at 0.27K and closes at 8K, while the other one ($\Delta_{\mathrm{2}}$), as large as 12 meV, is isotropic and eventually evolves into a pseudogap closing at 40K. Both, the two-gap BTK and Dynes models can well reproduce our data, demonstrating $\Delta _{\mathrm{1\thinspace }}$should be associated with the proximity-induced superconductivity in the topological Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$ layer, while $\Delta_{\mathrm{2}}$ may be attributed to an intrinsically-doped FeTe thin film at the interface.