Anyon dispersion from non-uniform magnetic field on the sphere

Abstract: The discovery of fractional quantum anomalous Hall states in moir\'e systems has raised the interesting possibility of realizing phases of itenerant anyons. Anyon dispersion is only possible in the absence of continuous magnetic translation symmetry (CMTS). Motivated by this, we consider anyons on the sphere in the presence of a non-uniform magnetic field which breaks the ${\rm SU}(2)$ rotation symmetry, the analog of CMTS on the sphere, down to a ${\rm U}(1)$. This allows us to study the energy dispersion of the anyons as a function of $L_z$ angular-momentum, while maintaining the perfect flatness of single-particle dispersion. Parametrizing the non-uniform field by a real parameter $R$ which concentrates the field at the north (south) pole for $R>1$ ($R < 1$), we use exact diagonalization to verify nonzero energy-angular momentum dispersion for any $R \neq 1$. For our choice of non-uniform field, we show that any $p$-body correlation function evaluated in the space of Laughlin quasiholes for any value of $R$ can be mapped exactly to a corresponding $p$-body correlation function in uniform field. In the thermodynamic limit, this enables us to analytically compute the interaction-generated spatially varying potential felt by the anyons and the resulting anyon dispersion exactly, up to an overall scaling constant, for the cases of short-range and Coulomb interaction. The anyon dispersion in our model describes azimuthal motion around the sphere at a constant height, similar to spin precession. Our work therefore serves as a concrete demonstration that interaction alone can generate nonzero anyon dispersion in the presence of inhomogeneous magnetic field.