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

Abstract

These authors contributed equally to this work 2The single-layered ruthenate Sr2RuO4 has attracted a great deal of interest as a spin-triplet superconductor with an order parameter that may potentially break time reversal invariance and host half-quantized vortices with Majorana zero modes. While the actual nature of the superconducting state is still a matter of controversy, it has long been believed that it condenses from a metallic state that is well described by a conventional Fermi liquid. In this work we use a combination of Fourier transform scanning tunneling 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 10meV, 38meV and 70meV 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 may provide important information for understanding the superconducting state. This work opens up a unique approach to revealing the superconducting order parameter in this compound.

High-Resolution Photoemission on Sr2RuO4 Reveals Correlation-Enhanced Effective Spin-Orbit Coupling and Dominantly Local Self-Energies

“…Moreover, attributing the entire curvature of Σ m in our data to electron-phonon coupling would result in unrealistic coupling constants far into the polaronic regime, which is hard to reconcile with the transport properties of Sr 2 RuO 4 [10][11][12]. We also note that a recent scanning tunneling microscope (STM) study reported very strong kinks in the β and γ sheets of Sr 2 RuO 4 [49], which is inconsistent with our data. We discuss the reason for this discrepancy in appendix A.…”

“…These deviations are reproduced by our DMFT calculations suggesting that the cause of these non-linearities are local electronic correlations. Our results thus call for a revision of earlier reports of strong electron-lattice coupling in Sr 2 RuO 4 [29][30][31][46][47][48][49][50]. We finally quantify the effective spin-orbit coupling (SOC) strength and confirm its enhancement due to correlations predicted theoretically [21,23,51].…”

“…We thus conclude that the experiments reported in Ref. [49] probed the surface states of Sr 2 RuO 4 . This is fully consistent with the strong low-energy kinks and overall enhanced low-energy renormalization seen by ARPES in the surface bands [50,90].…”

“…Wang et al [49] have recently probed the low-energy electronic structure of Sr 2 RuO 4 by STM. Analyzing quasiparticle interference patterns along the ΓX and ΓM high-symmetry directions, they obtained band dispersions with low Fermi velocities and strong kinks at 10 meV and 37 meV.…”

Spectroscopic evidence of nematic fluctuations in LiFeAs

“…The geometry of the Friedel oscillations in momentum space has successfully been used to reconstruct the electronic band structure of many correlated materials [20][21][22][23][24][25][26][27]. This includes, since very recently, even the detection of subtle band renormalizations due to electron-boson interactions [25][26][27]. in the superconducting state which is renormalized due to electron-boson coupling giving rise to the well-known kink-like structures above and below the Fermi level at energies indicated by dashed lines (the inset shows the bare band in red).…”