Weyl discs: theoretical prediction

TL;DR

This paper predicts the emergence of Weyl discs in quantum systems with dynamical parameters, extending the concept of Weyl points to finite regions in parameter space through theoretical analysis and specific examples.

Contribution

It introduces the concept of Weyl discs arising from soft constraints in quantum systems, providing theoretical predictions and concrete calculations for specific setups.

Findings

Weyl discs occur in the quasi-classical limit with soft constraints.

Two states are nearly degenerate over a finite 2D region in parameter space.

Concrete models include Weyl points in superconducting structures and Weyl excitons.

Abstract

A variety of quantum systems exhibits Weyl points in their spectra where two bands cross in a point of three-dimensional parameters space with conical dispersion in the vicinity of the point. We consider theoretically the soft constraint regime where the parameters are dynamical quantum variables. We have shown that in general the soft constraints, in quasi-classical limit, result in Weyl discs where two states are (almost) degenerate in a finite 2d region of the 3d parameter space. We provide concrete calculations for two setups: Weyl point in a four-terminal superconducting structure and a Weyl exciton, i.e., a bound state of Weyl electron and a massive hole.