Quasiparticle Interference of the van-Hove singularity in Sr$_2$RuO$_4$

TL;DR

This study uses quasiparticle interference imaging to investigate the van Hove singularity in Sr$_2$RuO$_4$, revealing how surface structural distortions influence its electronic properties and potential implications for superconductivity.

Contribution

It provides the first detailed electronic structure mapping of the van Hove singularity in Sr$_2$RuO$_4$'s surface layer, highlighting the role of octahedral rotations.

Findings

The van Hove singularity's dispersion was successfully traced.

Detection is facilitated by octahedral rotations in the surface layer.

Structural distortions significantly affect the electronic properties.

Abstract

The single-layered ruthenate Sr$_2$RuO$_4$ is one of the most enigmatic unconventional superconductors. While for many years it was thought to be the best candidate for a chiral $p$-wave superconducting ground state, desirable for topological quantum computations, recent experiments suggest a singlet state, ruling out the original $p$-wave scenario. The superconductivity as well as the properties of the multi-layered compounds of the ruthenate perovskites are strongly influenced by a van Hove singularity in proximity of the Fermi energy. Tiny structural distortions move the van Hove singularity across the Fermi energy with dramatic consequences for the physical properties. Here, we determine the electronic structure of the van Hove singularity in the surface layer of Sr$_2$RuO$_4$ by quasiparticle interference imaging. We trace its dispersion and demonstrate from a model calculation accounting for the full vacuum overlap of the wave functions that its detection is facilitated through the octahedral rotations in the surface layer.