Dynamics of doublon-holon pairs in Hubbard two-leg ladders

TL;DR

This study investigates how the geometry of Hubbard two-leg ladders influences the dynamics of holon-doublon pairs, revealing significant differences from one-dimensional chains due to the spin-gap and inter-leg coupling effects.

Contribution

It provides the first detailed analysis of doublon-holon pair dynamics in Hubbard two-leg ladders, highlighting the impact of ladder geometry and inter-leg coupling on excitation propagation.

Findings

Doublon-holon dynamics are strongly affected by ladder geometry and spin-gap presence.

Weak inter-leg coupling results resemble Hubbard chains with parameter renormalization.

Strong inter-leg coupling leads to notable differences in doublon speed and double occupancy.

Abstract

The dynamics of holon-doublon pairs is studied in Hubbard two-leg ladders using the time-dependent Density Matrix Renormalization Group method. We find that the geometry of the two-leg ladder, that is qualitatively different from a one-dimensional chain due to the presence of a spin-gap, strongly affects the propagation of a doublon-holon pair. Two distinct regimes are identified. For weak inter-leg coupling, the results are qualitatively similar to the case of the propagation previously reported in Hubbard chains, with only a renormalization of parameters. More interesting is the case of strong inter-leg coupling where substantial differences arise, particularly regarding the double occupancy and properties of the excitations such as the doublon speed. Our results suggest a connection between the presence of a spin gap and qualitative changes in the doublon speed, indicating a weak coupling between the doublon to magnetic excitations.