Two-dimensional Schrödinger operators with non-local singular potentials
Lukáš Heriban, Markus Holzmann, Christian Stelzer-Landauer, Georg Stenzel, Matěj Tušek
TL;DR
This work develops a rigorous extension-theoretic framework for two-dimensional Schrödinger operators with non-local singular potentials supported on a Lipschitz curve $Σ$, yielding a self-adjoint operator $T_B$ parameterized by compact Hermitian $B$ on $L^2(Σ;\mathbb{C}^2)$. Using a tailored generalized boundary triple, the authors derive a Krein-type resolvent formula and a Birman-Schwinger principle to characterize the spectrum, showing a stable essential spectrum $[0,\infty)$ and a richly structured discrete spectrum ranging from finite to infinite with accumulation at $-\infty$ under suitable $B$. They compare these non-local transmission conditions to classical $\,δ$-shell and oblique transmissions, and establish an explicit non-relativistic limit linking the Schrödinger model to a relativistic, non-local Dirac model studied in HT23. Overall, the paper provides a versatile operator-analytic framework for non-local surface interactions with concrete spectral consequences and a clear relativistic correspondence.
Abstract
In this paper we introduce and study a family of self-adjoint realizations of the Laplacian in $L^2(\mathbb{R}^2)$ with a new type of transmission conditions along a closed bi-Lipschitz curve $Σ$. These conditions incorporate jumps in the Dirichlet traces both of the functions in the operator domains and of their Wirtinger derivatives and are non-local. Constructing a convenient generalized boundary triple, they may be parametrized by all compact hermitian operators in $L^2(Σ;\mathbb{C}^2)$. Whereas for all choices of parameters the essential spectrum is stable and equal to $[0, +\infty)$, the discrete spectrum exhibits diverse behaviour. While in many cases it is finite, we will describe also a class of parameters for which the discrete spectrum is infinite and accumulates at $-\infty$. The latter class contains a non-local version of the oblique transmission conditions. Finally, we will connect the current model to its relativistic counterpart studied recently in [L. Heriban, M. Tušek: Non-local relativistic $δ$-shell interactions].
