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Presence of Delocalized Ti 3d Electrons in Ultrathin Single-Crystal SrTiO 3

Strontium titanate (STO), with a wide spectrum of emergent properties such as ferroelectricity and superconductivity, has received significant attention in the community of strongly correlated materials. In the strain-free STO film grown on the SrRuO buffer layer, the existing polar nanoregions can...

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Bibliographic Details
Published in:Nano letters 2022-02, Vol.22 (4), p.1580-1586
Main Authors: Chiu, Chun-Chien, Ho, Sheng-Zhu, Lee, Jenn-Min, Shao, Yu-Cheng, Shen, Yang, Liu, Yu-Chen, Chang, Yao-Wen, Zheng, Yun-Zhe, Huang, Rong, Chang, Chun-Fu, Kuo, Chang-Yang, Duan, Chun-Gang, Huang, Shih-Wen, Yang, Jan-Chi, Chuang, Yi-De
Format: Article
Language:English
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Summary:Strontium titanate (STO), with a wide spectrum of emergent properties such as ferroelectricity and superconductivity, has received significant attention in the community of strongly correlated materials. In the strain-free STO film grown on the SrRuO buffer layer, the existing polar nanoregions can facilitate room-temperature ferroelectricity when the STO film thickness approaches 10 nm. Here we show that around this thickness scale, the freestanding STO films without the influence of a substrate show the tetragonal structure at room temperature, contrasting with the cubic structure seen in bulk form. The spectroscopic measurements reveal the modified Ti-O orbital hybridization that causes the Ti ion to deviate from its nominal 4+ valency (3d configuration) with excess delocalized 3d electrons. Additionally, the Ti ion in TiO octahedron exhibits an off-center displacement. The inherent symmetry lowering in ultrathin freestanding films offers an alternative way to achieve tunable electronic structures that are of paramount importance for future technological applications.
ISSN:1530-6984
1530-6992
DOI:10.1021/acs.nanolett.1c04434