Fermi surface sheet-dependent band splitting in Sr2RuO4revealed by high-resolution angle-resolved photoemission spectroscopy

Abstract

High-resolution angle-resolved photoemission measurements have been carried out on Sr${}_{2}$RuO${}_{4}$. We observe clearly two sets of Fermi surface sheets near the ($\ensuremath{\pi}$,0)-(0,$\ensuremath{\pi}$) line, which are most likely attributed to the surface and bulk Fermi surface splitting of the $\ensuremath{\beta}$ band. This is in strong contrast to the nearly null surface and bulk Fermi surface splitting of the $\ensuremath{\alpha}$ band, although both have identical orbital components. Extensive band structure calculations are performed by considering various scenarios, including structural distortion, spin-orbit coupling, and surface ferromagnetism. However, none of them can explain such a qualitative difference of the surface and bulk Fermi surface splitting between the $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ sheets. This unusual behavior points to an unknown order on the surface of Sr${}_{2}$RuO${}_{4}$ that remains to be uncovered. Its revelation will be important for studying and utilizing novel quantum phenomena associated with the surface of Sr${}_{2}$RuO${}_{4}$ as a result of its being a possible $p$-wave chiral superconductor and a topological superconductor.