Phenomenology of bond and flux orders in kagome metals

Despite much experimental and theoretical work, the nature of the charge order in the kagome metals belonging to the family of materials AV$_3$Sb$_5$ (A=Cs,Rb,K) remains controversial. A crucial ingredient for the identification of the ordering in these materials is their response to external perturbations, such as strain or magnetic fields. To this end, we provide a comprehensive symmetry classification of the possible charge orders in kagome materials with a $2\times2$ increase of the unit cell. Motivated by the experimental reports of time-reversal-symmetry breaking and rotational anisotropy, we consider the interdependence of flux and bond orders. Deriving the relevant Landau free energy for possible orders, we study the effect of symmetry-breaking perturbations such as strain and magnetic fields. Our results, thus, provide a roadmap for future tests of these intricate orders.
Comment: 15 pages (+7 pages appendix), 4 figures (+6 figures appendix)