Strong orbital-dependent $d$-band hybridization and Fermi surface reconstruction in metallic Ca$_{2-x}$Sr$_{x}$RuO$_4$

The layered ruthenate Ca$_{2-x}$Sr$_x$RuO$_4$ displays diverse ground states ranging from a superconductor ($x$$=$2) to a Mott insulator ($x$$=$0), accompanied by structural distortions.We investigate the effects of RuO$_6$ rotation on Ru 4$d$ band structures in the metallic phase (0.5$<$$x$$<$2) by first-principles electronic structure calculations. Our study reveals that the symmetry lowering due to RuO$_6$ rotation induces a strong orbital-dependent t$_ {2g}$- e$_g$ hybridization. As a result, only the d$_{xy}$ band among three t$_{2g} $ bands is severely affected and thereby the Fermi surface is reconstructed, forming a new electron-like d$_{xy}$ Fermi surface near $\Gamma$ and nested sections near $x$$=$0.5. These findings should provide a new insight on the electron correlation in the material.