X-ray studies of unconventional charge correlations in kagome metals

Kagome metals host an interesting coexistence of features in their band structures capable of promoting both correlated and topologically nontrivial electronic states.  These include flat band features due to hopping interference, saddle points generating Van Hove singularities, as well as Dirac crossings. These electronic degrees of freedom can also intertwine with lattice instabilities to generate novel charge density wave and charge ordered states.  In this talk, I will discuss recent x-ray scattering measurements of unusual charge correlations that develop in two classes of kagome compounds.  The first is the class of AV₃Sb₅ (A=K, Rb, Cs) kagome superconductors which are known to possess band fillings close to the Van Hove points in their band structures. The nature of charge correlations that develop and how they evolve as the filling about the Van Hove points is varied will be discussed.  The second class of materials discussed will be an unusual lattice instability and charge order in the ScV₆Sn₆ kagome metal.  Here a sterically driven lattice instability generates frustrated charge order with anomalous short-range correlations.  The importance of modern, diffuse scattering x-ray measurements for discerning short-range correlations in these new classes of kagome metals will be stressed throughout.