Excitonic quasiparticles in a spin-orbit Mott insulator

TL;DR

This paper reports the discovery of an excitonic quasiparticle in a spin-orbit Mott insulator, revealing fundamental charge-neutral excitations with properties akin to Landau quasiparticles, which could shed light on high-temperature superconductivity.

Contribution

It provides the first observation of an exciton dressed with magnons acting as a quasiparticle in a Mott insulator, advancing understanding of correlated electron systems.

Findings

Observation of a composite excitonic quasiparticle in Sr2IrO4

The exciton exhibits a finite quasiparticle residue and long lifetime

The narrow linewidth reveals intrinsic dynamics related to high-temperature superconductivity

Abstract

In condensed matter systems, out of a large number of interacting degrees of freedom emerge weakly coupled particles, in terms of which most physical properties are described. For example, Landau quasiparticles (QP) determine all electronic properties of a normal metal. The lack of identification of such QPs is major barrier for understanding myriad exotic properties of correlated electrons, such as unconventional superconductivity and non-Fermi liquid behaviours. Here, we report the observation of a composite particle in a Mott insulator Sr2IrO4---and exciton dressed with magnons---that propagates with the canonical characteristics of a QP: a finite QP residue and a lifetime longer than the hopping time scale. The dynamics of this charge-neutral bosonic excitation mirrors the fundamental process of the analogous one-hole propagation in the background of ordered spins, for which a well-defined QP has never been observed. The much narrower linewidth of the exciton reveals the same intrinsic dynamics that is obscured for the hole and is intimately related to the mechanism of high temperature superconductivity.