• Zeljkovic, Ilija
• Wang, Yuxuan
• Husain, Ali
• Fradkin, Eduardo
• Madhavan, Vidya
• Rak, Melinda
• Maeno, Yoshiteru
• Derry, Philip
• Damascelli, Andrea
• Vig, Sean
• Kogar, Anshul
• Abbamonte, Peter
• Santos, Luiz H.
• Walkup, Daniel
• Wang, Zhenyu
• Scaffidi, Thomas

Abstract

The single-layered ruthenate Sr<SUB>2</SUB>RuO<SUB>4</SUB> 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 Sr<SUB>2</SUB>RuO<SUB>4</SUB>. 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 Sr<SUB>2</SUB>RuO<SUB>4</SUB> 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.

Topics

• impedance spectroscopy
• dispersion
• layered
• one-dimensional
• electron energy loss spectroscopy
• scanning tunneling microscopy
• scanning tunnelling spectroscopy