Effect of Anisotropic Hybridization in YbAlB${}_4$ Probed by Linear Dichroism in Core-Level Hard X-ray Photoemission Spectroscopy

Abstract

We have probed the crystalline electric-field ground states of pure $|J=7/2,J_z=\pm 5/2⟩$ as well as the anisotropic $c$-$f$ hybridization in both valence fluctuating systems $\alpha$- and $\beta$-YbAlB${}_4$ by linear polarization dependence of angle-resolved core level photoemission spectroscopy. Interestingly, the small but distinct difference between \abyb was found in the polar angle dependence of linear dichroism, indicating the difference in the anisotropy of $c$-$f$ hybridization which may be essential to a heavy Fermi liquid state in $\alpha$-YbAlB${}_4$ and a quantum critical state in $\beta$-YbAlB${}_4$.