Surface and bulk electronic structure of the unconventional superconductor Sr₂RuO₄: unusual splitting of the<i>β</i>band

Abstract

We present an angle resolved photoemission study of the surface and bulk\nelectronic structure of the single layer ruthenate Sr$_2$RuO$_4$. As the early\nstudies of its electronic structure by photoemission and scanning tunneling\nmicroscopy were confronted with a problem of surface reconstruction, surface\naging was previously proposed as a possible remedy to access the bulk states.\nHere we suggest an alternative way by demonstrating that, in the case of\nSr$_2$RuO$_4$, circularly polarised light can be used to disentangle the\nsignals from the bulk and surface layers, thus opening the possibility of\ninvestigating many-body interactions both in bulk and surface bands. The\nproposed procedure results in improved momentum resolution, which enabled us to\ndetect an unexpected splitting of the surface $\\beta$ band. We propose that\nspin--orbit splitting might be responsible for this, and discuss possible\nrelations of the newly observed surface feature to topological matter.\n