Femtosecond dynamics of decoupled superlattice zones in 4Hb–TaSe2 single crystals

Abstract

Strongly correlated electronic crystal systems marked by temperature-dependent phase transitions often feature an emergence of new structural periodicities, arising from an interplay between modulated electron density and periodic lattice distortion. We investigate the structural evolution of superlattice clusters in 4Hb–TaSe2 single crystals on a subpicosecond and atomic resolution via femtosecond electron diffraction (FED). The superlattice clusters comprise of two six-member rings each, related by a rotational symmetry and held in position by Coulombic mode repulsion. The two six-member rings are decoupled into two possible zones, which are further decoupled into respective site-specific satellite reflections in the reciprocal space. Governed by the interlayer interactions and the electron diffraction simulation analysis, FED measurements are used to demonstrate the suppression and dynamics of the decoupled superlattice zones. The simultaneous temporal evolution of the two CDW reflection orders are assigned to the decoupled Raman-active Ag and soft phonon modes previously reported on an isomorphic crystal structure (4Hb–TaS2). It is found that the charge density wave amplitude mode dominates over the corresponding phase mode.