Absence of localized \(5d^1\) electrons in KTaO\(_3\) interface superconductors

• Published in: arXiv.org 2023-03
• Main Authors: Cai, Xinqiang, Kim, Jungho, Martinelli, Leonardo, Florio, Piero, Corti, Matteo, Qiao, Weiliang, Sun, Yanqiu, Niu, Jiasen, Faure, Quentin, Sahle, Christoph, Qiu, Qingzheng, Xiao, Qian, Zheng, Xiquan, Li, Qizhi, Zou, Changwei, Jiang, Xinyi, Ghiringhelli, Giacomo, Han, Wei, Xie, Yanwu, Lu, Yi, Marco Moretti Sala, Peng, Yingying
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Electron gas; Electrons; Hysteresis; Interfaces; Spectrum analysis; Superconductivity; Superconductors; Transition temperature; X ray absorption; X-ray spectroscopy
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2303.01811

Recently, an exciting discovery of orientation-dependent superconductivity was made in two-dimensional electron gas (2DEG) at the interfaces of LaAlO\(_3\)/KTaO\(_3\) (LAO/KTO) or EuO/KTaO\(_3\) (EuO/KTO). The superconducting transition temperature can reach a \(T_c\) of up to \(\sim\) 2.2 K, which is significantly higher than its 3\(d\) counterpart LaAlO\(_3\)/SrTiO\(_3\) (LAO/STO) with a \(T_c\) of \(\sim\) 0.2 K. However, the underlying origin remains to be understood. To uncover the nature of electrons in KTO-based interfaces, we employ x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray spectroscopy (RIXS) to study LAO/KTO and EuO/KTO with different orientations. We reveal the absence of \(dd\) orbital excitations in all the measured samples. Our RIXS results are well reproduced by calculations that considered itinerant \(5d\) electrons hybridized with O \(2p\) electrons. This suggests that there is a lack of localized Ta \(5d^1\) electrons in KTO interface superconductors, which is consistent with the absence of magnetic hysteresis observed in magneto-resistance (MR) measurements. These findings offer new insights into our understanding of superconductivity in Ta \(5d\) interface superconductors and their potential applications.