Principal Investigator Nuh Gedik
Iridium oxides are unique 5d electronic systems in which spin-orbit coupling, electronic bandwidth and on-site Coulomb interactions occur on comparable energy scales. Their interplay can stabilize a novel spin-orbital entangled Jeff = 1/2 Mott insulating state in which a correlation gap is opened by only moderate Coulomb interactions owing to a spin-orbit coupling induced band narrowing.
A critical temperature TN and the localized Jeff = 1/2 moments undergo long-range ordering. However owing to an absence of clear anomalies at TN in transport, thermodynamic and optical conductivity data, there have been conflicting interpretations about how the insulating gap behaves across TN. We use time-resolved optical spectroscopy, which is highly sensitive to the existence of energy gaps, to study the temperature evolution of the electronic structure of Sr2IrO4. Taking advantage of qualitatively distinct relaxation dynamics of photo-excited carriers exhibited by gapped and gapless systems, we find a clear change in the ultrafast dynamics across TN indicating a gap opening concomitant with antiferromagnetic order.