Quasi-particle interference of the van Hove singularity in Sr2RuO4

A Kreisel,R Fittipaldi,V Granata,P J Hirschfeld,T Berlijn,X Kong,A Vecchione,C A Marques,L C Rhodes,P Wahl

doi:10.1038/s41535-021-00401-x

Abstract

The single-layered ruthenate Sr2RuO4 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 Sr2RuO4 by quasi-particle 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.

Highlights

Strontium Ruthenate, Sr2RuO4, has played a leading role in discussions of unconventional superconductivity since its discovery almost three decades ago[1,2,3,4,5,6]
As discussed in the introduction, we begin with the premise that understanding the quasiparticle interference (QPI) in the normal state[19,21,22] will be essential to the identification of the symmetry and structure of the superconducting gap in Sr2RuO4 by scanning tunneling microscopy (STM)
The first is the dramatic suppression of the features in the measured spectrum that originate from bands with dominant dxy orbital content, compared with a calculation of N(q, ω) using the lattice Green’s function with bulk electronic bands as done in refs. 19,21, where QPI was modeled by ignoring any dxy contribution to the trace and density of states

Summary

Introduction

Strontium Ruthenate, Sr2RuO4, has played a leading role in discussions of unconventional superconductivity since its discovery almost three decades ago[1,2,3,4,5,6]. Much of the interest in the community centered on the possibility of chiral p-wave pairing, but the compound has attracted attention because of its structural similarity to the cuprates, Fermi liquid behavior at low temperatures, and the availability of very clean samples with highquality surfaces. Direct measurement of the superconducting gap by, e.g., angular resolved photoemission spectroscopy (ARPES), could provide important guidance, as it did in the cuprates. STM is a more appropriate tool, which due to its very high energy resolution that can be achieved at low temperatures and the ability to obtain information about the momentum- and phaseresolved structure of the superconducting gap through quasiparticle interference (QPI) imaging[12,13] promises to resolve the most pressing questions about the superconducting properties of

Methods

Results

Conclusion