Gain/Loss-free Non-Hermitian Metamaterials

TL;DR

This paper demonstrates that non-Hermitian physics can be realized in Hermitian systems through interfaces, specifically between topological insulators and conductors, leading to dissipative non-reciprocal wave propagation.

Contribution

It introduces a novel approach to realize non-Hermitian effects in Hermitian systems via interfaces, supported by experimental demonstration of exotic non-Hermitian behavior.

Findings

Wave propagation along the interface shows dissipative non-reciprocity.

The interface exhibits non-Hermitian characteristics without gain or loss.

Experimental realization of non-Hermitian behavior in topological insulator-conductor junctions.

Abstract

The ease of using optical gain/loss provides a fertile ground for experimental explorations of non-Hermitian (NH) physics. Without gain/loss, can we realize the NH effect in a Hermitian system? The interface between the coupled Hermitian subsystems is a natural object for NH physics due to the nonconservative process on it. However, it is still far from enduing the interface with rich NH physics. Here, a junction between the topological insulator and the conductor is considered, where the interface can be effectively described by a NH Hamiltonian--such NH character is ascribed to the conductor self-energy of a reservoir. As a consequence of that, we show the wave propagation along the interface exhibits dissipative non-reciprocity (dubbed non-Bloch transport), which was believed to be unique in NH systems. Moreover, the meta-materialization of tight-binding models is also studied by identifying their equivalent connectivity, enabling us to demonstrate the above exotic NH behavior of the interface experimentally. Our work provides a conceptually rich avenue to construct NH systems for both optics and electronics.