Here we report on a new kind of compound, X{\delta}Ir4X12-{\delta} (X = P, As), the first hole-doped skutterudites superconductor. We provide atomic resolution images of the caging As atoms using scanning transmission electron microscopy (STEM). By inserting As atoms into the caged structure under a high pressure, superconductivity emerges with a maximum transition temperature (Tc) of 4.4 K (4.8 K) in IrAs3 (IrP3). In contrast to all of the electron-doped skutterudites, the electronic states around the Fermi level in X{\delta}Ir4X12-{\delta} are dominated by the caged X atom, which can be described by a simple body-centered tight-binding model, implying a distinct paring mechanism. Our density functional theory (DFT) calculations reveal an intimate relationship between the pressure-dependent local-phonon mode and the enhancement of Tc. The discovery of X{\delta}Ir4X12-{\delta} provides an arena to investigate the uncharted territory of hole-doped skutterudites, and the method proposed here represents a new strategy of carrier doping in caged structures, without introducing extra elements.
@article{arxiv.2204.07522,
title = {Caging-Pnictogen-Induced Superconductivity in Skutterudites IrX3 (X = As, P)},
author = {Cuiying Pei and Tianping Ying and Qinghua Zhang and Xianxin Wu and Tongxu Yu and Yi Zhao and Lingling Gao and Changhua Li and Weizheng Cao and Qing Zhang and Andreas P. Schnyder and Lin Gu and Xiaolong Chen and Hideo Hosono and Yanpeng Qi},
journal= {arXiv preprint arXiv:2204.07522},
year = {2022}
}