Formation of spinful dark excitons in Hubbard systems with magnetic superstructures

TL;DR

This paper demonstrates how electron-electron interactions and magnetic superstructures in Hubbard models can lead to the formation of spinful dark excitons, detectable via spectral and optical measurements, with implications for correlated insulator experiments.

Contribution

It introduces a novel mechanism for dark exciton formation in Hubbard systems with magnetic superstructures, analyzed through advanced MPS simulations.

Findings

Dark excitons appear in specific spin channels after excitation.

Additional spectral bands and peaks in optical conductivity are observed.

Recombination occurs on longer timescales than simulation can capture.

Abstract

The possibility to form excitons in photoilluminated correlated materials is central from fundamental and application oriented perspectives. In this paper we show how the interplay of electron-electron interactions and a magnetic superstructure leads to the formation of a peculiar spinful dark exciton, which can be detected in ARPES-type experiments and optical measurements. We study this by using matrix product states (MPS) to compute the time evolution of single-particle spectral functions and of the optical conductivity following an electron-hole excitation in a class of one-dimensional correlated band-insulators, simulated by Hubbard models with on-site interactions and alternating local magnetic fields. An excitation in only one specific spin direction leads to an additional band in the gap region of the spectral function only in the spin direction unaffected by the excitation and to an additional peak in the optical conductivity. As both is formed only after the excitation, this is interpreted as a dark exciton, which shows only in one spin direction. Recombination of the excitation happens on much longer time scales than the ones amenable to MPS. We discuss implications for experimental studies in correlated insulator systems.