Influence of spin and orbital fluctuations on Mott-Hubbard exciton dynamics in LaVO3 thin films

Abstract

Recent optical conductivity measurements reveal the presence of Hubbard excitons in certain Mott insulators. In light of these results, it is important to revisit the dynamics of these materials to account for excitonic correlations. We investigate time-resolved excitation and relaxation dynamics as a function of temperature in perovskite-type LaVO 3 thin films using ultrafast optical pump-probe spectroscopy. LaVO 3 undergoes a series of phase transitions at roughly the same critical temperature T C ∼ = 140 K, including a second-order magnetic phase transition (PM − → AFM) and a first-order structural phase transition, accompanied by C-type spin order and G-type orbital order. Ultrafast optical pump-probe spectroscopy at 1.6 eV monitors changes in the spectral weight of the Hubbard exciton resonance which serves as a sensitive reporter of spin and orbital fluctuation dynamics. We observe dramatic slowing down of the spin, and orbital dynamics in the vicinity of T C ∼ = 140 K, reminiscent of a second-order phase transition, despite the (weakly) first-order nature of the transition. We emphasize that since it is spectral weight changes that are probed, the measured dynamics are not reflective of conventional exciton generation and recombination, but are related to the dynamics of Hubbard exciton formation in the presence of a fluctuating many-body environment.

Optical and excitonic properties of transition metal oxide perovskites by the Bethe-Salpeter equation

“…The exciton binding energies (listed in Table VI) fall within the 120 meV to 190 meV range and are overall smaller than their cubic nonmagnetic counterparts (with the exception of LaVO 3 ). The predicted higher E xb for LaVO 3 is consistent with the larger experimental value of Lovinger et al [61] (∼0.6 eV). Recent experimental optical conductivity measurements [60] also highlight a splitting of the low-energy structure (visible as an additional shoulder at lower temperatures) which has been related to excitonic effects [61][62][63] and is correctly reproduced by the BSE data (but completely absent in the RPA curve).…”

“…The predicted higher E xb for LaVO 3 is consistent with the larger experimental value of Lovinger et al [61] (∼0.6 eV). Recent experimental optical conductivity measurements [60] also highlight a splitting of the low-energy structure (visible as an additional shoulder at lower temperatures) which has been related to excitonic effects [61][62][63] and is correctly reproduced by the BSE data (but completely absent in the RPA curve). Compared to the full BSE, mBSE introduces an error ranging between 10% (LaScO 3 ) and 37% (LaVO 3 ), with a mean absolute error of 0.20 eV.…”

Optical and excitonic properties of transition metal oxide perovskites by the Bethe-Salpeter equation

“…The exciton binding energies (listed in Table VI) fall within the 120 meV -190 meV range and are overall smaller than their cubic non-magnetic counterparts (with the exception of LaVO 3 ). The predicted higher E xb for LaVO 3 is consistent with the larger experimental value of Lovinger et al [63] (∼ 0.6 eV). Recent experimental optical conductivity measurements [62] also highlight a splitting of the low-energy structure (visible as an additional shoulder at lower temperatures) which has been related to excitonic effects [63][64][65] and is correctly reproduced by the BSE data (but completely absent in the RPA curve).…”

“…The predicted higher E xb for LaVO 3 is consistent with the larger experimental value of Lovinger et al [63] (∼ 0.6 eV). Recent experimental optical conductivity measurements [62] also highlight a splitting of the low-energy structure (visible as an additional shoulder at lower temperatures) which has been related to excitonic effects [63][64][65] and is correctly reproduced by the BSE data (but completely absent in the RPA curve). Compared to the full BSE, mBSE introduces an error ranging between 10% (LaScO 3 ) and 37% (LaVO 3 ), with a mean absolute error of 0.20 eV.…”

Colloquium: Nonthermal pathways to ultrafast control in quantum materials

“…Similarly to what occurs in thermal equilibrium, in the vicinity of a second-order transition, spatial fluctuations of the order parameter diverge, and the exponential rate with which the ordered phase is reinstated vanishes following a power law. This has been seen, for example, in the electronic recovery of charge order in perovskite manganites (Beaud et al, 2014) and La 1/3 Sr 2/3 FeO 3 (Zhu et al, 2018), in the suppression dynamics of the charge density wave in LaTe 3 (Zong et al, 2019a), as well as in the spin and orbital dynamics in YVO 3 and GdVO 3 (Yusupov et al, 2010b), and LaVO 3 (Lovinger et al, 2020). Divergent slow dynamics also characterize the ultrafast suppression of the nematic electronic order in FeSe (Shimojima et al, 2019) and in iron pnictides (Patz et al, 2014).…”