Caging-Pnictogen-Induced Superconductivity in Skutterudites IrX<sub>3</sub> (X = As, P)
Cuiying Pei, Tianping Ying, Qinghua Zhang, Xianxin Wu, Tongxu Yu, Yi Zhao, Lingling Gao, Changhua Li, Weizheng Cao, Qing Zhang, Andreas P. Schnyder, Lin Gu, Xiaolong Chen, Hideo Hosono, Yanpeng Qi
Abstract
Here, we report on a new kind of compound, XδIr4X12−δ (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 XδIr4X12−δ are dominated by the caged X atom, which can be described by a simple body-centered tight-binding model, implying a distinct pairing 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 XδIr4X12−δ 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.