Studies of single layer FeSe nanoribbons on SrTiO$_{\mathrm{\mathbf{3}}}$

Nanoribbons of single layer FeSe are grown on SrTiO$_{\mathrm{3}}$ substrates by molecular beam epitaxy, and their topographic and electronic properties studied by in situ scanning tunneling microscopy/spectroscopy. Systematic tunneling spectroscopy investigation carried out at 6K shows a superconducting gap of 20 meV for ribbons larger than 5 nm. Furthermore, edge states are also detected at the edges of these ribbons, suggesting the coexistence of topological and superconducting states in single layer FeSe/ SrTiO$_{\mathrm{3}}$.