We investigate THz conductivity dynamics in NdNiO₃ and EuNiO₃ ultrathin films (15 unit cells, u.c., ∼5.7 nm thick) following a photoinduced thermal quench into the metallic state and reveal a clear contrast between first- and second-order dynamics. While in EuNiO₃ the conductivity recovers exponentially, in NdNiO₃ the recovery is nonexponential and slower than a simple thermal model. Crucially, it is consistent with first-order dynamics and well-described by a 2d Avrami model, with supercooling leading to metastable phase coexistence on the nano- to mesoscopic scale. This novel observation is a fundamentally dynamic manifestation of the first-order character of the insulator-to-metal transition, which the nanoscale thickness of our films and their fast cooling rate enable us to detect. The large transients seen in our films are promising for fast electronic (and magnetic) switching applications.

中文翻译：

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镍超薄薄膜电导率恢复动力学中的成核和生长瓶颈。

我们研究了NdNiO ₃和EuNiO ₃超薄膜（15个晶胞，uc，约5.7 nm厚）中的太赫兹电导率动力学，经过光诱导的热猝灭进入了金属态，并揭示了一级和二级动力学之间的明显对比。在EuNiO _3中，电导率呈指数恢复，在NdNiO _3中与简单的热模型相比，恢复是非指数的，并且速度较慢。至关重要的是，它与一阶动力学是一致的，并由2d Avrami模型很好地描述，并且过冷导致纳米到介观尺度的亚稳态相共存。这种新颖的观察是绝缘子到金属过渡的一阶特征的根本动力学表现，我们薄膜的纳米级厚度及其快速冷却速率使我们能够检测到。在我们的电影中看到的大瞬态对于快速的电子（和磁性）开关应用很有希望。