Single-particle and collective mode couplings associated with 1- and 2-directional electronic ordering in metallic RTe$_3$ (R = Ho, Dy, Tb)

TL;DR

This study investigates how phonons couple with collective modes and single-particle excitations in charge-density wave states of RTe3 compounds, revealing mode mixing phenomena and deviations from mean-field behavior during phase transitions.

Contribution

It provides new insights into the mode coupling dynamics and the evolution of charge-density wave order in RTe3, especially regarding the transition from 1d to 2d ordering.

Findings

Resonant mode-mixing of amplitude mode with a phonon at 1.75 THz affects the CDW gap.

The 1d-CDW transition initially follows mean-field behavior but deviates below T_c1.

Additional mode mixing occurs in the 2d-CDW state without soft mode observation.

Abstract

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 RTe_3 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 (AM) we find that while the transition to a 1d-CDW ordered state at T_{c1} initially proceeds in an exemplary mean-field (MF) -like fashion, below T_{c1}, \Delta_{CDW} is depressed and departs from the MF behavior. The effect is apparently triggered by resonant mode-mixing of the amplitude mode (AM) 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 DyTe_3 and HoTe_3, additional much weaker mode mixing is evident but no soft mode is observed.