image: a Fermi arc surface state of Weyl semimetals. Oppositely charged Weyl points (WPs, indicated by red and blue dots) are connected by surface Fermi arcs (red and blue arcs) on the opposite surfaces. The arrows denote the propagation directions of the chiral Fermi arc surface states. b Under a magnetic field (or pseudomagnetic field (PMF)), the bulk states and the closed Fermi loops composing two surface Fermi arcs giving rise to chiral Landau levels (gray dashed lines with arrows) and one-sided chiral hinge states of Fermi arcs (red and blue arrows) at two diagonal hinges, which are the hallmark signatures of 3D QHE of Fermi arcs.
Credit: ©Science China Press
The discovery of the three-dimensional (3D) quantum Hall effect (QHE) of Fermi arcs in topological semimetals has fundamentally expanded our understanding of Hall physics. Unlike the traditional two-dimensional (2D) QHE, which features chiral edge states, this 3D counterpart is characterized by one-sided chiral hinge states. However, to date, these one-sided chiral hinge states have remained unobserved in experiments.
In a new study published in National Science Review, researchers at Southern University of Science and Technology (SUSTech) and their collaborators reported the first experimental observation of these one-sided chiral hinge states in a 3D inhomogeneous magnetic Weyl photonic crystal.
"The direct observation of these one-sided chiral hinge states is the 'smoking gun' for the 3D QHE of Fermi arcs," says Prof. Zhen Gao, the corresponding author of the study. "Our findings not only experimentally verify the 3D QHE of Fermi arcs but also reveal a new physical mechanism for robust light transport in 3D space, with potential applications in designing robust topological photonic devices".