Zero-energy modes, fractional fermion numbers and the index theorem in a vortex-Dirac fermion system
arXiv:2003.06575 · doi:10.3390/sym12030373
Abstract
Physics of topological materials have attracted much attention from both physicists and mathematicians recently. The index and the fermion number of Dirac fermions play an important role in topological insulators and topological superconductors. A zero-energy mode exists when Dirac fermions couple to objects with soliton-like structure such as kinks, vortices, monopoles, strings and branes. We discuss a system of Dirac fermions interacting with a vortex and a kink. This kind of systems will be realized on the surface of topological insulators where Dirac fermions exist. The fermion number is fractionalized and this is related to the presence of fermion zero-energy excitation modes. A zero-energy mode can be regarded as a Majorana fermion mode when the chemical potential vanishes. Our discussion includes the case where there is a half-flux quantum vortex associated with a kink in a magnetic field in a bilayer superconductor. A normalizable wave function of fermion zero-energy mode does not exist in the core of the half-flux quantum vortex. The index of Dirac operator and the fermion number have additional contributions when a soliton scalar field has a singularity.
8 pages
References in corpus (6)
- Topological Field Theory of Time-Reversal Invariant Insulators
- Specular Andreev reflection in graphene
- Persistence of zero modes in a gauged Dirac model for bilayer graphene
- Kondo Effect in the Presence of Spin-Orbit Coupling
- Dirac fermions and Kondo effect
- Fractional skyrmion and absence of low-lying Andreev bound states in a micro fractional-flux quantum vortex