Strong in-plane anisotropy in the electronic structure of fixed-valence ${\hat{I}}^2$-LuAlB${}_4$

Abstract

The origin of intrinsic quantum criticality in the heavy-fermion superconductor ${\hat{I}}^2$-YbAlB${}_4$ has been attributed to strong Yb valence fluctuations and its peculiar crystal structure. Here, we assess these contributions individually by studying the isostructural but fixed-valence compound ${\hat{I}}^2$-LuAlB${}_4$. Quantum oscillation measurements and DFT calculations reveal a Fermi surface markedly different from that of ${\hat{I}}^2$-YbAlB${}_4$, consistent with a `large' Fermi surface there. We also find an unexpected in-plane anisotropy of the electronic structure, in contrast to the isotropic Kondo hybridization in ${\hat{I}}^2$-YbAlB${}_4$.

6 pages, 4 figures