title: Excitonic quasiparticles in a spin-orbit Mott insulator.
abstract: In condensed matter systems, out of a large number of interacting degrees of freedom emerge weakly coupled quasiparticles (QPs), in terms of which most physical properties are described. The lack of identification of such QPs is a 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 quasi-two-dimensional spin-1/2 antiferromagnet Sr2IrO4--an 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 excitation mirrors the fundamental process of the analogous one-hole propagation in the background of spins-1/2, and reveals the same intrinsic dynamics that is obscured for a single, charged-hole doped into two-dimensional cuprates.
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Jungho
authors.initials: J
authors.lastname: Kim
authors.affiliation: Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Daghofer
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: A H
authors.initials: AH
authors.lastname: Said
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: T
authors.initials: T
authors.lastname: Gog
authors.affiliation: Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany.
authors.forename: J
authors.initials: J
authors.lastname: van den Brink
authors.affiliation: Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Khaliullin
authors.affiliation: 1] Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany [2] Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Kim