Variation of Electron-electron interaction in pyrochlore structures

Jianyu Li; Ji Liu; Mingjun Han; Waqas Haider; Yusuke Nomura; Ho-Kin Tang

paper

Variation of Electron-electron interaction in pyrochlore structures

arXiv:2409.01123

Abstract

We conduct a comprehensive \textit{ab initio} investigation of electron-electron interactions within the pyrochlore structures of R $_{2}$ Ru $_{2}$ O $_{7}$ , R $_{2}$ Ir $_{2}$ O $_{7}$ , Ca $_{2}$ Ru $_{2}$ O $_{7}$ , and Cd $_{2}$ Ru $_{2}$ O $_{7}$ , where R denotes a rare-earth element. Utilizing a multiorbital Hubbard model, we systematically explore the effects of various rare-earth elements and applied high pressure on the correlation strength in these compounds. Our calculations on the Coulomb interaction parameter $U$ and the bandwidth $W$ reveal that the chemical pressure for R $_{2}$ Ru $_{2}$ O $_{7}$ and R $_{2}$ Ir $_{2}$ O $_{7}$ leads to an unusual increase in $U / W$ ratio, hence, increase in correlation strength. Contrary to conventional understanding of bandwidth control, our study identifies that the Hubbard $U$ is more influential than the bandwidth $W$ behind the metal-insulator landscape of R $_{2}$ Ru $_{2}$ O $_{7}$ and R $_{2}$ Ir $_{2}$ O $_{7}$ , leading to an interaction-controlled metal-insulator transition. We also find unexpected behavior in physical pressure. Whereas physical pressure leads to a decrease in the correlation strength $U / W$ as usual in R $_{2}$ Ru $_{2}$ O $_{7}$ , the effect is notably small in Ca $_{2}$ Ru $_{2}$ O $_{7}$ and Cd $_{2}$ Ru $_{2}$ O $_{7}$ , which provides an important clue to understanding unusual pressure-induced metal-insulator transition observed experimentally.