Photoenhanced excitonic correlations in a Mott insulator with nonlocal interactions

Abstract

We investigate the effect of nonlocal interactions on the photo-doped Mott insulating state of the twodimensional Hubbard model using a nonequilibrium generalization of the dynamical cluster approximation. In particular, we compare the situation where the excitonic states are lying within the continuum of doublonholon excitations to a set-up where the excitons appear within the Mott gap. In the first case, the creation of nearest-neighbor doublon-holon pairs by excitations across the Mott gap results in enhanced excitonic correlations, but these excitons quickly decay into uncorrelated doublons and holons. In the second case, photoexcitation results in long-lived excitonic states. While in a low-temperature equilibrium state, excitonic features are usually not evident in single-particle observables such as the photoemission spectrum, we show that the photo-excited nonequilibrium system can exhibit in-gap states associated with the excitons. The comparison with exact-diagonalization results for small clusters allows us to identify the signatures of the excitons in the photo-emission spectrum.

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

“…A spreading of localized FM excitations via magnons can provide an alternative decay channel, which is not captured by the approximate theoretical description considered here and would be an interesting subject for future investigations. The binding of singlons and triplons and its impact on the recombination rate is not properly captured in DMFT, but should not play an important role in the dilute photoexcitation limit explored in the experiments 55 . The experimental observation of oscillations slightly above T N cannot be explained by our theoretical treatment, which relies on a mean-field decoupling of the spin-spin interaction.…”

Nonequilibrium dynamics of $α$-RuCl$_{3}$ -- a time-resolved magneto-optical spectroscopy study

“…For sufficiently small excitation densities holon-doublon pair recombination via magnon emission appears to dom- inate, the hopping of unbound holons and doublons in the IFR effectively perturbs the long-range zigzag order. Theory predicts that in the strong excitation regime indeed a larger fraction of the excitons separates into unbound doublons and holons [20]. The most intriguing observation in the IFR is the analogous power-law scaling behavior (∝ F −0.7 ) observed for the time scale of the gap collapse after photoexcitation in the excitonic insulator materials e.g.…”

“…Further, besides being a spin liquid candidate material, the presence of Mott-Hubbard physics accompanied by strong spin-orbit coupling and the role of excitons in photoexcited α-RuCl 3 makes it enormously complex with unique photoinduced dynamics providing an opportunity to investigate many-body interactions. Understanding dynamical excitonic correlations and their interaction with a magnetically ordered background is a fundamental scientific question [20]. Optical spectroscopy and ellipsometry revealed a narrow line shape and asymmetry of the peak in the optical conductivity at around 1.1 eV associated with the optical gap, which suggest strong electron-hole interaction, and a small shoulder extending into the Mott gap indicating the presence of an excitonic bound state [21,22].…”

Effects of frustration on the nonequilibrium dynamics of photo-excited lattice systems

“…[35][36][37] Implementations of cluster-based DMFT methods for out-of-equilibrium problems are however still rare and nonequilibrium studies of nonlocal correlation effects represent a frontier in this research field. [38][39][40][41] In the present work, we reveal possible fingerprints of geometric frustration in photo-doped Mott insulating systems. The photo-excitation of electrons across a large Mott gap leads to the creation of long-lived doublon (holon) type charge carriers in the upper (lower) Hubbard band.…”

“…(1), we employ the nonequilibrium generalization of the dynamical cluster approximation (DCA) in combination with a non-crossing approximation (NCA) impurity solver. [41][42][43] Within this formalism, the cluster reference system (without bath) is represented by the cluster Hamiltonian…”