Revealing Hund superdispersion with tunneling spectroscopy

TL;DR

This paper uses tunneling spectroscopy combined with theoretical modeling to identify Hund physics signatures in Sr$_2$RuO$_4$, revealing superdispersive spectral features linked to Hund coupling.

Contribution

It provides the first direct experimental evidence of Hund-induced spectroscopic features in a multi-orbital quantum material.

Findings

Experimental features match theoretical predictions for Hund physics.

Spectroscopic signatures are linked to non-monotonous self-energy in Hund metals.

Results open new avenues for probing correlation effects in quantum materials.

Abstract

In cuprate superconductors, electron-electron repulsion results in characteristic spectroscopic features known as `waterfalls', where the sharp quasiparticle dispersion transitions into broad Hubbard bands. However, in multi-orbital systems, the additional Hund coupling results in behavior that defies the conventional Mott--Hubbard paradigm, creating qualitatively distinct `superdispersive' features in the spectral function. Here, we use tunneling spectroscopy to reveal this signature of Hund physics in Sr$_2$RuO$_4$. By combining density functional theory, dynamical mean-field theory, and continuum local density of states calculations, we show that the experimental features are in excellent agreement with theoretical predictions and intimately linked to the non-monotonous energy dependence of the real part of the self-energy in a Hund metal. Our results provide direct experimental evidence for Hund-induced spectroscopic features and open a new route to probing correlation effects in quantum materials.