Multi-orbital nature of the spin fluctuations in Sr$_2$RuO$_4$

TL;DR

This paper uses advanced theoretical methods to analyze the multi-orbital spin fluctuations in Sr$_2$RuO$_4$, confirming experimental spectra and revealing orbital contributions to the dominant spin fluctuations.

Contribution

It provides a realistic multi-orbital analysis of spin susceptibility in Sr$_2$RuO$_4$ using DFT+DMFT, beyond weak-coupling approaches.

Findings

Experimental fluctuation spectrum up to 80 meV is confirmed by theory.

Peak at ${f Q}_i$ involves nearly equal contributions from all Ru-$4d$-$t_{2g}$ orbitals.

Spin fluctuations are cooperative, involving multiple orbitals.

Abstract

The spin susceptibility of strongly correlated Sr$_2$RuO$_4$ is known to display a rich structure in reciprocal space, with a prominent peak at ${\bf Q}_i$=$(0.3,0.3,0)$. It is still debated if the resulting incommensurate spin-density-wave fluctuations foster unconventional superconductivity at low temperature or compete therewith. By means of density functional theory combined with dynamical mean-field theory, we reveal the realistic multi-orbital signature of the (dynamic) spin susceptibility beyond existing weak-coupling approaches. The experimental fluctuation spectrum up to 80 meV is confirmed by theory. Furthermore, the peak at ${\bf Q}_i$ is shown to carry nearly equal contributions from each of the Ru$(4d)$-$t_\mathrm{2g}$ orbitals, pointing to a cooperative effect resulting in the dominant spin fluctuations.