Dynamics of a single exciton in strongly correlated bilayers

TL;DR

This paper develops an effective theory for a single exciton in a bilayer quantum antiferromagnet, revealing how its spectral properties vary with interlayer coupling and phase, with implications for optical measurements.

Contribution

It introduces a new theoretical framework for exciton dynamics in bilayer antiferromagnets, incorporating spin wave approximations and confinement effects.

Findings

Coherent quasiparticle peak in disordered phase at large coupling

Ladder spectrum due to Ising confinement in Néel phase

Spectral features observable in dielectric and optical measurements

Abstract

We formulated an effective theory for a single interlayer exciton in a bilayer quantum antiferromagnet, in the limit that the holon and doublon are strongly bound onto one interlayer rung by the Coulomb force. Upon using a rung linear spin wave approximation of the bilayer Heisenberg model, we calculated the spectral function of the exciton for a wide range of the interlayer Heisenberg coupling \alpha=J_{\perp}/Jz. In the disordered phase at large \alpha, a coherent quasiparticle peak appears representing free motion of the exciton in a spin singlet background. In the N\'{e}el phase, which applies to more realistic model parameters, a ladder spectrum arises due to Ising confinement of the exciton. The exciton spectrum is visible in measurements of the dielectric function, such as c-axis optical conductivity measurements.