VO₂ (110)ᵣ 超薄膜中的电子相分离与非二聚化绝缘相的出现
Electronic phase separation and emergence of a nondimerized insulating phase in VO$_2$ $(110)_{\mathit{R}}$ ultrathin films
- Tohoku University（东北大学）
- High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）
- Université Paris-Saclay（巴黎-萨克雷大学）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究通过原位光电子能谱和X射线吸收谱，发现VO₂ (110)ᵣ超薄膜中存在电子相分离，其非二聚化绝缘相比例随厚度减小呈指数增长，维度降低引发的莫特不稳定性是该相出现的关键驱动力。
AI中文摘要：
利用原位光电子能谱和X射线吸收谱，我们研究了VO₂/TiO₂ (110)超薄膜中电子结构与V-V二聚化的厚度依赖性，其中沿cᵣ轴的一维V-V链位于薄膜平面内。在VO₂ (110)ᵣ薄膜中，与VO₂ (001)ᵣ薄膜不同，沿表面法向的维度降低预计不会对V-V二聚化施加几何约束。然而，厚薄膜中观测到的与温度驱动金属-绝缘体转变相关的特征光谱变化持续到1.5 nm，而在1 nm时观测到无V-V二聚化的绝缘电子相。该行为与VO₂ (001)ᵣ的报道高度相似，表明维度降低导致的莫特不稳定性增强是VO₂超薄膜中非二聚化绝缘相出现的共同且必要驱动力。同时，与VO₂ (001)ᵣ不同，VO₂ (110)ᵣ中的非二聚化绝缘相与表现出温度驱动金属-绝缘体转变的相共存，其比例随厚度减小呈指数增长，在1 nm时成为主导相，对应的有效临界厚度估计为2.2 nm。这些结果表明，V-V链的几何取向通过应变介导的相竞争决定了电子相分离的空间演化。
英文摘要：
Using in situ photoemission spectroscopy and x-ray absorption spectroscopy, we investigated the thickness dependence of the electronic structure and V-V dimerization in VO$_2$/TiO$_2$ (110) ultrathin films, in which the one-dimensional V-V chains along the $c_{\mathit{R}}$ axis lie in the film plane. In VO$_2$ $(110)_{\mathit{R}}$ films, the reduction in dimensionality along the surface-normal direction is not expected to impose a geometric constraint on V-V dimerization, unlike in VO$_2$ $(001)_{\mathit{R}}$ films. Nevertheless, the characteristic spectral changes associated with the temperature-driven metal-insulator transition observed in thick films persist down to 1.5 nm, whereas at 1 nm an insulating electronic phase is observed without V-V dimerization. This behavior is highly similar to that reported for VO$_2$ $(001)_{\mathit{R}}$, suggesting that the enhancement of Mott instability resulting from reduced dimensionality is a common and essential driving force for the emergence of the nondimerized insulating phase in VO$_2$ ultrathin films. Meanwhile, unlike in VO$_2$ $(001)_{\mathit{R}}$, the nondimerized insulating phase in VO$_2$ $(110)_{\mathit{R}}$ coexists with the phase exhibiting the temperature-driven metal-insulator transition. Its fraction increases exponentially with decreasing thickness and becomes dominant at 1 nm. The corresponding effective critical thickness is estimated to be 2.2 nm. These results imply that the geometric orientation of the V-V chains dictates the spatial evolution of electronic phase separation via strain-mediated phase competition.
