Eigenvalues of a one-dimensional Dirac operator pencil

TL;DR

This paper investigates the spectral properties of a one-dimensional Dirac operator pencil, focusing on the conditions for zero modes, their asymptotic distribution, and the influence of potential characteristics, with implications for graphene waveguides.

Contribution

It provides new insights into the distribution of coupling constants leading to zero modes and reveals the impact of potential sign variation and arithmetic properties on the spectrum.

Findings

Distribution of zero modes depends on potential sign variation

Potential gaps influence the asymptotic distribution of coupling constants

Variable sign potentials can produce complex eigenvalues

Abstract

We study the spectrum of a one-dimensional Dirac operator pencil, with a coupling constant in front of the potential considered as the spectral parameter. Motivated by recent investigations of graphene waveguides, we focus on the values of the coupling constant for which the kernel of the Dirac operator contains a square integrable function. In physics literature such a function is called a confined zero mode. Several results on the asymptotic distribution of coupling constants giving rise to zero modes are obtained. In particular, we show that this distribution depends in a subtle way on the sign variation and the presence of gaps in the potential. Surprisingly, it also depends on the arithmetic properties of certain quantities determined by the potential. We further observe that variable sign potentials may produce complex eigenvalues of the operator pencil. Some examples and numerical calculations illustrating these phenomena are presented.