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# Quasiparticle interference and strong electron–mode coupling in the quasi-one-dimensional bands of Sr2RuO4

## Abstract

The single-layered ruthenate Sr2RuO4 is presented as a potential spin-triplet superconductor with an order parameter that may break time-reversal invariance and host half-quantized vortices with Majorana zero modes. Although the actual nature of the superconducting state is still a matter of controversy, it is believed to condense from a metallic state that is well described by a conventional Fermi liquid. In this work we use a combination of Fourier transform scanning tunnelling spectroscopy (FT-STS) and momentum-resolved electron energy loss spectroscopy (M-EELS) to probe interaction effects in the normal state of Sr2RuO4. Our high-resolution FT-STS data show signatures of the β-band with a distinctly quasi-one-dimensional (1D) character. The band dispersion reveals surprisingly strong interaction effects that dramatically renormalize the Fermi velocity, suggesting that the normal state of Sr2RuO4 is that of a ‘correlated metal’ where correlations are strengthened by the quasi-1D nature of the bands. In addition, kinks at energies of approximately 10 meV, 38 meV and 70 meV are observed. By comparing STM and M-EELS data we show that the two higher energy features arise from coupling with collective modes. The strong correlation effects and the kinks in the quasi-1D bands could provide important information for understanding the superconducting state.

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## Acknowledgements

We thank Z. Wang, H. Lin, J.C. Davis and S. Kivelson for useful conversations. STM work was supported by US Department of Energy, Scanned Probe Division under Award Number DE-SC0014335. The work was supported in part by the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4860. Y.M. acknowledges the support from the JSPS KAKENHI Grant No. JP15H05852. Theoretical work was supported in part by the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant No. GBMF4305 at the Institute for Condensed Matter Theory of the University of Illinois (L.H.S. and Y.W.), and by a grant of the National Science Foundation No. DMR1408713 at the University of Illinois (E.F.). M-EELS experiments were supported by the Center for Emergent Superconductivity, DOE #DE-AC02-98CH10886. P.A. acknowledges support from Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4542. T.S. acknowledges the financial support of the Clarendon Fund Scholarship, the Merton College Domus and Prize Scholarships, and the University of Oxford.

## Author information

Authors

### Contributions

Z.W. and D.W. contributed equally to this work. Z.W., D.W. and V.M. designed the STM experiments, analysed the data and wrote the paper. STM experiments were performed by D.W., Z.W. and I.Z. Y.M. was responsible for single-crystal growth and structural analysis. A.D. helped with conceiving the experiment, data analysis and comparison with ARPES. E.F., L.H.S. and Y.W. conceived the theoretical explanation for this work. P.D., and T.S. performed analytical model calculations. M.R., S.V., A.K., A.H. and P.A. were involved in the M-EELS studies.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

## Supplementary information

### Supplementary information

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Wang, Z., Walkup, D., Derry, P. et al. Quasiparticle interference and strong electron–mode coupling in the quasi-one-dimensional bands of Sr2RuO4. Nature Phys 13, 799–805 (2017). https://doi.org/10.1038/nphys4107

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• DOI: https://doi.org/10.1038/nphys4107

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