Single-Particle and Collective Mode Couplings Associated with 1-and 2-Directional Electronic Ordering in Metallic RTe3 (R=Ho,Dy,Tb)

The coupling of phonons with collective modes and single-particle gap excitations associated with one- (1d) and two-directional (2d) electronically driven charge-density wave (CDW) ordering in metallic RTe3 is investigated as a function of rare-earth ion chemical pressure (R=Tb,Dy,Ho) using femtosecond pump-probe spectroscopy. From the T dependence of the CDW gap Delta(CDW) and the amplitude mode, we find that while the transition to a 1d-CDW ordered state at T-c1 initially proceeds in an exemplary mean-field-like fashion, below T-c1, Delta(CDW) is depressed and departs from the mean-field behavior. The effect is apparently triggered by resonant mode mixing of the amplitude mode with a totally symmetric phonon at 1.75 THz. At low temperatures, when the state evolves into a 2d-CDW ordered state at T-c2 in the DyTe3 and HoTe3, additional much weaker mode mixing is evident but no soft mode is observed.