Recently, an exciting discovery of orientation-dependent superconductivity was made in two-dimensional electron gas (2DEG) at the interfaces of LaAlO3/KTaO3 (LAO/KTO) or EuO/KTaO3 (EuO/KTO). The superconducting transition temperature can reach a Tc of up to ∼ 2.2 K, which is significantly higher than its 3d counterpart LaAlO3/SrTiO3 (LAO/STO) with a Tc of ∼ 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 5d1 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.
@article{arxiv.2303.01811,
title = {Absence of localized $5d^1$ electrons in KTaO$_3$ interface superconductors},
author = {Xinqiang Cai and Jungho Kim and Leonardo Martinelli and Piero Florio and Matteo Corti and Weiliang Qiao and Yanqiu Sun and Jiasen Niu and Quentin Faure and Christoph Sahle and Qingzheng Qiu and Qian Xiao and Xiquan Zheng and Qizhi Li and Changwei Zou and Xinyi Jiang and Giacomo Ghiringhelli and Wei Han and Yanwu Xie and Yi Lu and Marco Moretti Sala and Yingying Peng},
journal= {arXiv preprint arXiv:2303.01811},
year = {2023}
}