Group Structure of Wilson Loops in 2D Models with 2- and 4-Band Energy Spectra
We consider a tight-binding model defined by a matrix Hamiltonian over 2D Brillouin zone. Multiband energy spectrum gives rise to a non-Abelian gauge structure set by the Berry connections. The corresponding curvature $F_{μν}$ vanishes throughout the Brillouin zone except an isolated points where $F_{μν}$ is singular. Combining the singular behaviour of $F_{μν}$ with non-Abelian Stokes theorem allows to avoid the path ordering procedure in studying the structure of Wilson loops. 2D models with 2-band and 4-band energy spectra are considered as a demonstrative examples and the group structure of the corresponding Wilson loops is revealed.
cond-mat.mes-hall↗