Direct observation of superconducting gaps in iron-based superconductors by laser ARPES

Abstract

We have developed a new apparatus for carrying out ultra-high energy resolution laser-excited angle-resolved photoemission spectroscopy (laser ARPES). The achieved energy resolution is ~ 70 μeV at a sample temperature ~ 1.5 K. As a test case, we have measured the superconducting gap of elemental metal Sn (Tc = 3.7 K). We have used this laser-ARPES apparatus, to directly observe the superconducting gap of various iron-based superconductors. The spectra of FeTe0.6Se0.4 below Tc show a very clear temperature dependent superconducting coherence peak. Preliminary momentum-dependent results indicate an anisotropic superconducting gap in FeTe0.6Se0.4.