Tunable Dirac nodal line in orthorhombic RuO${}_2$

Abstract

Pressure evolution of RuO2 is studied using single-crystal x-ray diffraction in a diamond anvil cell, combined with \textit{ab initio} band-structure calculations. The tetragonal rutile structure transforms into the orthorhombic CaCl${}_2$-type structure above 13 GPa under quasi-hydrostatic pressure conditions. This second-order transition is ferroelastic in nature and accompanied by tilts of the RuO${}_6$ octahedra. Orthorhombic RuO${}_2$ is expected to be paramagnetic metal, similar to ambient-pressure RuO${}_2$. It shows the increased $t_{2g}-e_g$ crystal-field splitting that is responsible for the pressure-induced color change. It further features the Dirac nodal line that shifts across the Fermi level upon compression.

arXiv comment8 pages with appendix, 8 figures