Non-Hermitian funneling in anisotropic media

Abstract: Non-Hermitian skin effect (NHSE) has emerged as a distinctive phenomenon enabling non-Bloch wave manipulation. However, it has been limited to discrete lattices requiring fine-tuned onsite gain/loss or asymmetric couplings. Here, moving beyond these discrete models, we realize novel NHSE in uniform media by leveraging anisotropy of non-Hermitian density tensors. Experiments based on an acoustic anisotropic metamaterial demonstrate that enabled by the NHSE, wave energy can be directed toward and collected at specific boundaries, exhibiting broadband and wide-angle characteristics. This intriguing phenomenon is termed non-Hermitian wave funneling, which, remarkably, occurs under uniform non-Hermitian modulations, free of fine-tuning. Furthermore, we identify a second-order NHSE, enabling wave funneling toward corners. Our work establishes a paradigm for exploring NHSE in uniform media, advancing the fundamental understanding of non-Hermitian physics and providing novel mechanisms for non-Bloch wave control in metamaterials or even natural materials without delicate tuning.