Continuum Landau surface states in a non-Hermitian Weyl semimetal

Abstract: The surface states of topological phases, which owe their existence to bulk topological band invariants, possess many features of deep physical significance. In some instances, they can be linked to a quantum anomaly: the violation of a classical symmetry by a field theory through the emergence of a non-conserved current. This phenomenon was recently generalized to the non-Hermitian (NH) regime, in the form of an NH chiral anomaly occurring in the surfaces states of an NH Weyl phase. Here, we show that the anomalous NH current is mediated by continnum Landau modes (CLMs) an exotic class of NH eigenstates exhibiting both spatial localization and a continuous spectrum, contrary to the usual distinction between bound and free states. The conditions for which CLMs are normalized, and their scaling of localization length with magnetic field strength, are found to match the requirements of the NH anomaly equation. We also discuss the conditions under which these surface states can be probed experimentally, such as on metamaterial platforms. For instance, under open boundary conditions, the surface states are a mix of CLMs and skin modes induced by the NH skin effect, but the NH anomaly can be observed through transmission measurements under different magnetic fields.