Electronic structure dimensionality of the quantum-critical ferromagnet YbNi$_4$P$_2$

Abstract

YbNi$_4$P$_2$ is the first known ferromagnetic metal showing a second-order quantum phase transition. Current theoretical understanding rules out second order ferromagnetic quantum criticality in centrosymmetric 2D and 3D metals. Thus, studying the electronic structure of YbNi$_4$P$_2$ is of prime fundamental importance. Using angle-resolved photoemission spectroscopy, we experimentally prove the existence of 1D Fermi surface contours. In addition, our results demonstrate that part of the electronic structure of YbNi$_4$P$_2$ is made of states of higher dimensionality, thereby bringing into question the fact that ferromagnetic quantum criticality in centrosymmetric crystals, is exclusively found in 1D systems. Our experimental data show that the electronic structure of YbNi$_4$P$_2$ is a playground of mixed dimensionality, electron correlations, strong hybridization and spin-orbit coupling, all of them providing new insights in understanding the origin of ferromagnetic quantum criticality.