Cascade of pressure-induced competing charge density waves in the kagome metal FeGe

Electronic ordering is prevalent in correlated systems, which commonly exhibit competing interactions. Here, we use x-ray diffraction to demonstrate a cascade of pressure-induced order-disorder transformations, with propagation vectors qCDW=(12012), q∗=(131312), and q†=(131313), in the kagome metal FeGe. In the pressure interval between 4<p<10 GPa, qCDW and q∗ coexist and the spatial extent of the 3×3 order is nearly long range at ∼15 GPa, ∼30 unit cells. Above ∼25 GPa, the periodic lattice distortion has a propagation wave vector of q†=(131313) at room temperature. The cascade of phase transitions is captured by the Ising model of frustrated triangular lattices and modeled by Monte Carlo simulations based on the dimerization of trigonal Ge1. The pressure dependence of the integrated intensities and correlation lengths of qCDW, q∗, and q† demonstrating a competition between the 2×2 and 3×3 phases prove the tunability of order-disorder phase transitions under pressure and the rich landscape of metastable/fragile phases of FeGe.