Braiding fluxes in Pauli Hamiltonian

Abstract

Aharonov and Casher showed that Pauli Hamiltonians in two dimensions have gapless zero modes. We study the adiabatic evolution of these modes under the slow motion of $N$ fluxons with fluxes $\Phi_a\in\mathbb{R}$. The positions, $\mathbf{r}_a\in\mathbb{R}^2$, of the fluxons are viewed as controls. We are interested in the holonomies associated with closed paths in the space of controls. The holonomies can sometimes be abelian, but in general are not. They can sometimes be topological, but in general are not. We analyze some of the special cases and some of the general ones. Our most interesting results concern the cases where holonomy turns out to be topological which is the case when all the fluxons are subcritical, $\Phi_a<1$, and the number of zero modes is $D=N-1$. If $N\ge3$ it is also non-abelian. In the special case that the fluxons carry identical fluxes the resulting anyons satisfy the Burau representations of the braid group.