A scheme for realizing nonreciprocal interlayer coupling in bilayer topological systems

The exchange of energy and environment is inevitable in any physical system, so non-Hermitian systems that can be described by non-Hermitian Hamiltonians are ubiquitous. There are two kinds of non-Hermitian Hamiltonians, describing nonreciprocal systems with anisotropic coupling, also referred to as nonreciprocal coupling, and gain-loss systems.