Constructing Exceptional Knots and Links with Arbitrary Braiding Topology

Abstract

Exceptional knots and links represent a remarkable class of non-Hermitian metals in which exceptional degeneracies form knotted or linked manifolds in momentum space. Here, we report a universal construction framework for realizing exceptional knots and links with arbitrary braiding topology in 3D minimal two-band non-Hermitian systems. Our approach combines braid theory with semiholomorphic polynomials to establish a direct correspondence between braid words and non-Hermitian Bloch Hamiltonians. This framework enables the realization of a broad variety of exceptional configurations, including torus knots, lemniscate knots, nonfibred knots, hyperbolic knots, and multi-component links, within explicit tight-binding Hamiltonians. Furthermore, we demonstrate controllable topological transitions in which exceptional knots can be continuously untied through redistribution and reconnection of exceptional points, accompanied by transient exceptional chains and changes in spectral complex energy braiding. Our results establish a universal route toward programmable non-Hermitian knot topology and provide a versatile platform for exploring knotted band degeneracies and their associated physical phenomena across photonic, acoustic, mechanical, and cold-atom systems.