C10

The Dirac-Semimetal RuO2: From Topology to Functionality

Summary

Project C10 joined SFB 1170 in August 2020, and studies the functional Dirac semi-metal RuO2, a binary model oxide whose crystal symmetry-induced band structure topology produces a complex Fermi surface composed of Dirac nodal lines (DNL) and a flat band surface state (FBSS). Strong nesting of the DNLs is prone to Fermi surface instabilities, a postulated driving force of the recently discovered itinerant collinear antiferromagnetism (AFM) in RuO2 . In unison with the non-symmorphic rutile crystal field, this produces a non-relativistic spin splitting that breaks time-reversal symmetry in the band structure and is at the heart of key spintronic effects such as a large crystal anomalous Hall effect, charge-spin conversion and spin-torque, as well as giant and tunneling magnetoresistance. Based on our pulsed laser-deposited epitaxial RuO2 films (in collaboration with C08), we will em- ploy state-of the art micro-spectroscopy (STM/STS, spin-ARPES), magneto-transport experiments (in collaboration with the Würzburg-Dresden cluster of excellence Complexity and Topology in Quan- tum Matter, ctd.qmat; and with SPINTEC Grenoble), and theory (in collaboration with projects A09, C05 and C07), to establish the intricate link between fundamental band structure topology, electron correlation and spin-splitting phenomena in RuO2.