Frustrated charge order and competing charge density wave instabilities in ScV6Sn6

We study the stability of charge order in the kagome metal ScV6Sn6 using synchrotron x-ray diffraction (XRD) measurements. XRD data reveal high-temperature, short-range charge correlations at the wave vector of q=(1/3 , 1/3 , 1/2) whose inter-layer correlation lengths diverge upon cooling. At the charge order transition, this divergence is interrupted and long-range order freezes at the wave vector of q=(1/3 , 1/3 , 1/3), while disorder enables the charge correlations to persist at the q=(1/3 , 1/3 , 1/2) wave vector down to the lowest temperatures measured. Both long-range and short-range charge correlations seemingly arise from the same instability and both are rapidly quenched upon the doping of larger Y ions onto the Sc sites. Our results validate the theoretical prediction of the primary lattice instability at q=(1/3 , 1/3 , 1/2), and we present a qualitative picture of the frustration of charge order in this compound.