T-breaking density wave order in topological kagome metals

Kagome lattice metals $AV_ 3 Sb_ 5$ (A = Cs, K, Rb) host charge order derived from partially filled topologically non-trivial bands. In addition, recent muon spin resonance (muSR) measurements in $CsV_ 3 Sb_ 5$ detect an unambiguous signature of broken time reversal (T-) symmetry in the charge order phase. Here, we address the question: what is the character of emergent correlated phases derived from partially filled Chern bands? We advance a framework which enables a low energy tight-binding description of such a system using exponentially localized Wannier orbitals. The key conclusion is the existence of a density wave ground state, called DWt, which spontaneously breaks T - symmetry [1]. We argue that such a T-breaking property of the density wave is a fingerprint of the underlying band topology and is absent in other topologically trivial systems. We propose the DW$_t$ ordering as the mechanism for the charge density wave in the $AV_3Sb_5$ materials, and discuss the implications of our results for other correlated metallic systems that host topological bands.