Physics (Internal)

Dirac nodal lines and flat-band surface state in the functional oxide RuO2

This event is part of the Biophysics/Condensed Matter Seminar Series.

The efficiency and stability of RuO2 in electro-catalysis has made this material a subject of intense fundamental and industrial interest. The surface functionality is rooted in its electronic and magnetic properties – determined by a complex interplay of lattice-, spin-rotational, and time-reversal symmetries, as well as the competition between Coulomb- and kinetic energies. This interplay was predicted to produce a network of Dirac nodal lines (DNL), where the valence- and conduction bands touch along continuous lines in momentum space. Here we uncover direct evidence for three DNLs in RuO2 by angle resolved photoemission spectroscopy (ARPES). These DNLs give rise to a flat-band surface state (FBSS) that is readily tuned by the electrostatic environment, and that presents an intriguing platform for exotic correlation phenomena. Our findings support high spin-Hall conductivities and bulk magnetism in RuO2, and are likely related to its catalytic properties.

Vedran Jovic,1 Roland J. Koch,2 Swarup K. Panda,3 Helmuth Berger,4 Philippe Bugnon,4 Arnaud Magrez,4 Kevin E. Smith,1,5 Silke Biermann,3,6 Chris Jozwiak,2 Aaron Bostwick,2 Eli Rotenberg,2 and Simon Moser2,7

1 School of Chemical Sciences and Centre for Green Chemical Sciences, The University of Auckland, Auckland 1142, New Zealand

2 Advanced Light Source, E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

3 Centre de Physique Theorique, Ecole Polytechnique, CNRS-UMR7644, Université Paris-Saclay, 91128 Palaiseau, France

4 Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland

5Department of Physics, Boston University, Boston, Massachusetts 02215, USA

6 Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France