Supermetal-insulator transition in a non-Hermitian network model

TL;DR

This paper investigates a non-Hermitian 2D network model exhibiting a supermetal-insulator transition, skin effects, and exceptional points, revealing unique transmission properties and critical behavior influenced by balanced gain and loss.

Contribution

It introduces a non-Hermitian network model with novel contact effects, a supermetal transition, and critical phenomena, expanding the understanding of localization in non-Hermitian systems.

Findings

Discovery of a supermetal-insulator transition with exponential growth of transmission.

Identification of a non-Hermitian Dirac point with quantized critical transmission of 4.

Critical exponent for localization length divergence is approximately 1.

Abstract

We study a non-Hermitian and non-unitary version of the two-dimensional Chalker-Coddington network model with balanced gain and loss. This model belongs to the class D^dagger with particle-hole symmetry^dagger and hosts both the non-Hermitian skin effect as well as exceptional points. By calculating its two-terminal transmission, we find a novel contact effect induced by the skin effect, which results in a non-quantized transmission for chiral edge states. In addition, the model exhibits an insulator to 'supermetal' transition, across which the transmission changes from exponentially decaying with system size to exponentially growing with system size. In the clean system, the critical point separating insulator from supermetal is characterized by a non-Hermitian Dirac point that produces a quantized critical transmission of 4, instead of the value of 1 expected in Hermitian systems. This change in critical transmission is a consequence of the balanced gain and loss. When adding disorder to the system, we find a critical exponent for the divergence of the localization length \nu \approx 1, which is the same as that characterizing the universality class of two-dimensional Hermitian systems in class D. Our work provides a novel way of exploring the localization behavior of non-Hermitian systems, by using network models, which in the past proved versatile tools to describe Hermitian physics.