Surface and bulk electronic structure of unconventional superconductor Sr_2RuO_4: unusual splitting of the beta-band

TL;DR

This study uses circularly polarized light in photoemission experiments to distinguish surface and bulk electronic states in Sr₂RuO₄, revealing an unusual splitting of the beta-band potentially linked to spin-orbit effects and topological properties.

Contribution

It introduces a novel photoemission technique with circular polarization to separate surface and bulk signals in Sr₂RuO₄, enabling detailed analysis of their electronic structures.

Findings

Detected an unexpected splitting of the surface beta-band.

Proposed spin-orbit coupling as a cause for the splitting.

Discussed potential connections to topological matter.

Abstract

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