Pump-probe nano-optical experiments were used to study the light-induced insulator to metal transition (IMT) in thin films of vanadium dioxide (${\mathrm{VO}}_2$), a prototypical correlated electron system. We show that inhomogeneous optical contrast is prompted by spatially uniform photoexcitation, indicating an inhomogeneous photosusceptibility of ${\mathrm{VO}}_2$. We locally characterize temperature and time dependent variations of the photoexcitation threshold necessary to induce the IMT on picosecond timescales with hundred nanometer spatial resolution. We separately measure the critical temperature $T_L$, where the IMT onsets and the local transient electronic nano-optical contrast at the nanoscale. Our data reveal variations in the photosusceptibility of ${\mathrm{VO}}_2$ within nanoscopic regions characterized by the same critical temperature $T_L$ where metallic domains can first nucleate.

中文翻译：

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纳米级 VO2 薄膜的不均匀光敏感性

泵浦探针纳米光学实验用于研究二氧化钒薄膜中光致绝缘体到金属的转变（IMT）。${\mathrm{视氧浓度}}_2$），一个典型的相关电子系统。我们表明，不均匀的光学对比度是由空间均匀的光激发引起的，表明不均匀的光敏感性${\mathrm{视氧浓度}}_2$。我们局部表征了在皮秒时间尺度上以百纳米空间分辨率诱导 IMT 所需的光激发阈值随温度和时间的变化。我们分别测量临界温度${\mathrm{时间}}_L$，其中 IMT 开始，并且纳米级的局部瞬态电子纳米光学对比度。我们的数据揭示了光敏感性的变化${\mathrm{视氧浓度}}_2$在具有相同临界温度特征的纳米级区域内${\mathrm{时间}}_L$金属域可以首先成核的地方。