Unconventional Excitonic States with Phonon Sidebands in Layered Silicon Diphosphide

TL;DR

This paper reports the discovery of an unconventional excitonic state with phonon sidebands in layered silicon diphosphide, revealing complex many-particle interactions and their effects on optical properties in low-dimensional materials.

Contribution

It introduces a novel excitonic state with phonon sidebands in SiP$_2$, combining experimental and theoretical methods to elucidate exciton-phonon interactions in layered materials.

Findings

Observation of an unconventional excitonic state with phonon sidebands

Demonstration of linear dichroism and temperature-dependent energy shifts

Confirmation of exciton-phonon coupling through theoretical calculations

Abstract

Many-body interactions between quasiparticles (electrons, excitons, and phonons) have led to the emergence of new complex correlated states and are at the core of condensed matter physics and material science. In low-dimensional materials, unique electronic properties for these correlated states could significantly affect their optical properties. Herein, combining photoluminescence, optical reflection measurements and theoretical calculations, we demonstrate an unconventional excitonic state and its bound phonon sideband in layered silicon diphosphide (SiP$_2$), in which the bound electron-hole pair is composed of electrons confined within one-dimensional phosphorus$-$phosphorus chains and holes extended in two-dimensional SiP$_2$ layers. The excitonic state and the emergent phonon sideband show linear dichroism and large energy redshifts with increasing temperature. Within the $GW$ plus Bethe$-$Salpeter equation calculations and solving the generalized Holstein model non-perturbatively, we confirm that the observed sideband feature results from the correlated interaction between excitons and optical phonons. Such a layered material provides a new platform to study excitonic physics and many-particle effects.