Chiral edge states are the fingerprint of the bulk-edge correspondence in a Chern insula- tor. Co-propagating edge modes, known as antichiral edge states, have been predicted to occur in the so-called modified Haldane model describing a two-dimensional semi-metal with broken time reversal symmetry. These counterintuitive edge modes are argued to be immune to backscattering and extremely robust against disorder. Here, we investi- gate the robustness of the antichiral edge states in the presence of Anderson disorder. By computing different localization parameters, we show that these edge states are rela- tively fragile against disorder compared to the chiral modes. We also derive analytically the localization lengths of the AC edge states along and across a semi-infinite zigzag rib- bon. We show that these edge states have a schizophrenic behavior: they exhibit a large coherence length across the ribbon but a very short one along the zigzag boundary, which makes them fragile in the presence of disorder. Our work provides insights to improve the transport efficiency in the burgeoning fields of antichiral topological photonics and acoustics.
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We added Section IV Added paragraphs in the abstract, introduction and conclusion sections We added a figure (Fig.8) and three references 73-75
