Many-body effects on high-harmonic generation in Hubbard ladders

TL;DR

This paper investigates how many-body spin dynamics influence high-harmonic generation in Hubbard ladders, revealing complex excitation processes and deviations from conventional semiconductor behavior.

Contribution

It uncovers the role of interchain hopping and spin excitations in modifying HHG features in Hubbard ladder models, highlighting novel multi-excitation processes.

Findings

Spin dynamics significantly alter HHG spectra.

Interchain hopping causes loss of doublon-holon coherence.

Unconventional HHG involving three excitations identified.

Abstract

We show how many-body effects associated with background spin dynamics control the high-harmonic generation (HHG) in Mott insulators by analyzing the two-leg ladder Hubbard model. Spin dynamics activated by the interchain hopping $t_y$ drastically modifies the HHG features. When two chains are decoupled ($t_y=0$), HHG originates from the dynamics of coherent doublon-holon pairs because of spin-charge separation. With increasing $t_y$, the doublon-holon pairs lose their coherence due to their interchain hopping and resultant spin-strings. Furthermore, the HHG signal from spin-polarons -- charges dressed by spin clouds -- leads to an additional plateau in the HHG spectrum. For large $t_y$, we identify unconventional HHG processes involving $three$ elementary excitations -- two polarons and one magnon. Our results demonstrate the nontrivial nature of HHG in strongly correlated systems, and its qualitative differences to conventional semiconductors.