Dr. Zala Lenarčič from the Department for Theoretical Physics at Jožef Stefan Institute published “A Hubbard exciton fluid in a photo-doped antiferromagnetic Mott insulator” as a Nature Physics article, together with colleagues from California Institute of Technology (USA), University of California, Santa Barbara (USA) and University of Cologne (Germany). Their finding gives an experimental confirmation of the existence of Hubbard excitons in correlated material. These metastable non-equilibrium states have been theoretically anticipated in the doctoral thesis of Dr. Lenarčič under the supervision of Prof. Peter Prelovšek a decade ago.

The paper reports a transient formation of a Hubbard exciton fluid in the antiferromagnetic Mott insulator Sr2IrO4 using ultrafast terahertz conductivity. Following photo-excitation, creating free, oppositely charged particles causing a transient metallic response, the authors observe a rapid spectral-weight transfer from a Drude metallic response to a new non-equilibrium spectral feature. Latter is associated with binding of opposite charges, glued by the spin antiferromagnetic fluctuations into a new type of excitons.