Anomalous temperature dependence of high-harmonic generation in Mott insulators

TL;DR

This paper investigates how strong spin-charge coupling influences high-harmonic generation in Mott insulators, revealing an anomalous increase in HHG signal at lower temperatures due to complex many-body effects.

Contribution

It demonstrates that the temperature dependence of HHG in Mott insulators is governed by spin-charge interactions and thermal coherence, a novel insight into nonlinear optical responses of correlated materials.

Findings

HHG signal is enhanced at lower temperatures despite increasing gap.

The anomalous behavior is linked to spin-charge coupling and thermal effects.

The phenomenon is likely universal in Mott insulators and tunable via Coulomb interaction and dimensionality.

Abstract

We reveal the crucial effect of strong spin-charge coupling on high-harmonic generation (HHG) in Mott insulators. In a system with antiferromagnetic correlations, the HHG signal is drastically enhanced with decreasing temperature, even though the gap increases and the production of charge carriers is suppressed. This anomalous behavior, which has also been observed in recent HHG experiments on Ca$_2$RuO$_4$, originates from a cooperative effect between the spin-charge coupling and the thermal ensemble, and the strongly temperature-dependent coherence between charge carriers. We argue that the peculiar temperature dependence of HHG is a generic feature of Mott insulators, which can be controlled via the Coulomb interaction and dimensionality of the system. Our results demonstrate that correlations between different degrees of freedom, which are a characteristic feature of strongly correlated solids, have significant and nontrivial effects on nonlinear optical responses.