Abreu E, Meyers D, Thorsmølle V K, Zhang J, Liu X, Geng K, Chakhalian J, Averitt R D
Institute for Quantum Electronics, Department of Physics, ETH Zurich, 8093 Zurich, Switzerland.
Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078, United States.
Nano Lett. 2020 Oct 14;20(10):7422-7428. doi: 10.1021/acs.nanolett.0c02828. Epub 2020 Sep 14.
We investigate THz conductivity dynamics in NdNiO and EuNiO 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 EuNiO the conductivity recovers exponentially, in NdNiO 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.
我们研究了钕镍氧化物（NdNiO）和铕镍氧化物（EuNiO）超薄膜（15个晶胞，约5.7纳米厚）在光致热猝灭进入金属态后的太赫兹电导率动力学，并揭示了一级和二级动力学之间的明显差异。在EuNiO中，电导率呈指数恢复，而在NdNiO中，恢复是非指数的，且比简单的热模型慢。至关重要的是，它与一级动力学一致，并由二维阿弗拉米模型很好地描述，过冷导致纳米到介观尺度上的亚稳相共存。这一新颖的观察结果是绝缘体到金属转变的一级特性的一种基本动态表现，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这一特性。我们在薄膜中看到的大瞬态现象在快速电子（和磁性）开关应用方面很有前景。
