Strong in-plane anisotropy in the electronic structure of fixed-valence β−LuAlB4

Abstract

The origin of intrinsic quantum criticality in the heavy-fermion superconductor β-YbAlB4 has been attributed to strong Yb valence fluctuations and to its peculiar crystal structure. Here, we assess these contributions individually by studying the isostructural but fixed-valence compound β-LuAlB4. Quantum oscillation measurements and DFT calculations reveal a Fermi surface markedly different from that of β-YbAlB4, 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 hybrization in β-YbAlB4.At a quantum critical point (QCP), a continuous, zerotemperature phase transition occurs when the ordered and disordered phases are energetically degenerate. Usually, this requires tuning materials to some material-dependent critical pressure, composition or magnetic field [1]. However, there are rare case of 'intrinsic' QCPs which occur without tuning. Studying intrinsic QCPs aims at identifying robust mechanisms for quantum criticality, rising the prospect to link them to strange electronic phases and unconventional superconductivity [2,3].