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 ${\mathrm{LaVO}}_3$ thin films using ultrafast optical pump-probe spectroscopy. ${\mathrm{LaVO}}_3$ undergoes a series of phase transitions at roughly the same critical temperature $T_C\cong 140$ K, including a second-order magnetic phase transition ($\mathrm{PM}\stackrel{}{\to }\mathrm{AFM}$) 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 $T_C\cong 140$ 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.

中文翻译：

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自旋和轨道涨落对LaVO3薄膜中Mott-Hubbard激子动力学的影响

最近的光导率测量结果表明某些Mott绝缘子中存在Hubbard激子。鉴于这些结果，重要的是重新研究这些材料的动力学以说明激子相关性。我们研究钙钛矿型中时间分辨的激发和弛豫动力学随温度的变化${\mathrm{拉沃}}_3$ 超快光学泵浦-探针光谱法制备薄膜。 ${\mathrm{拉沃}}_3$ 在大致相同的临界温度下经历一系列相变 ${Ť}_C\cong 140$ K，包括二阶磁相变（$\mathrm{下午}\stackrel{}{\to }\mathrm{原子力显微镜}$）和一阶结构相变，并伴随 $C$型旋转顺序和 $G$型轨道顺序。1.6 eV的超快光学泵浦探针光谱法可监测Hubbard激子共振的光谱权重变化，该变化可作为自旋和轨道涨落动力学的敏感报告者。我们观察到自旋急剧减慢，并且在附近的轨道动力学${Ť}_C\cong 140$ K，让人联想到二阶相变，尽管过渡的（弱）一阶性质。我们强调，由于探测的是频谱权重变化，因此所测得的动力学并不反映常规激子的产生和重组，而是与存在多体波动环境的哈伯德激子形成的动力学有关。