Strain-modulated anisotropic electronic structure in superconducting RuO$_2$ films

Connor A. Occhialini; Luiz G. P. Martins; Shiyu Fan; Valentina Bisogni; Takahiro Yasunami; Maki Musashi; Masashi Kawasaki; Masaki Uchida; Riccardo Comin; Jonathan Pelliciari

arXiv · 2208.00718

Strain-modulated anisotropic electronic structure in superconducting RuO$_2$ films

Connor A. Occhialini·Luiz G. P. Martins·Shiyu Fan·Valentina Bisogni·Takahiro Yasunami·Maki Musashi·Masashi Kawasaki·Masaki Uchida·Riccardo Comin·Jonathan Pelliciari

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Abstract

The binary ruthenate, RuO$_2$, has been the subject of intense interest due to its itinerant antiferromagnetism and strain-induced superconductivity. The strain mechanism and its effect on the microscopic electronic states leading to the normal and superconducting state, however, remain undisclosed. Here, we investigate highly-strained epitaxial (110) RuO$_2$ films using polarization-dependent oxygen K-edge X-ray absorption spectroscopy (XAS). Through the detection of pre-edge peaks, arising from O:$2p$ - Ru:$4d$ hybridization, we uncover the effects of epitaxial strain on the orbital/electronic structure near the Fermi level. Our data show robust strain-induced shifts of orbital levels and a reduction of hybridization strength. Furthermore, we reveal a pronounced in-plane anisotropy of the electronic structure along the $[110]/[1\bar{1}0]$ directions naturally stemming from the symmetry-breaking epitaxial strain of the substrate. The $B_{2g}$ symmetry component of the epitaxially-enforced strain breaks a sublattice degeneracy, resulting in an increase of the density of states at the Fermi level ($E_F$), possibly paving the way to superconductivity. These results underscore the importance of the effective reduction from tetragonal to orthorhombic lattice symmetry in (110) RuO$_2$ films and its relevance towards the superconducting and magnetic properties.

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Connor A. Occhialini, Luiz G. P. Martins, Shiyu Fan, Valentina Bisogni, Takahiro Yasunami, Maki Musashi, Masashi Kawasaki, Masaki Uchida, Riccardo Comin, Jonathan Pelliciari. 2022-08-01. Strain-modulated anisotropic electronic structure in superconducting RuO$_2$ films. https://arxiv.org/abs/2208.00718

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