Infrared and Raman study of the charge-density-wave ground state

Auditorium B. Touschek (Laboratori Nazionali di Frascati, Via Enrico Fermi 40, Frascati)

Auditorium B. Touschek

Laboratori Nazionali di Frascati, Via Enrico Fermi 40, Frascati

Via Enrico Fermi 40 00044 Frascati

The question of the relationship between the effective dimensionality of a physical system and the symmetry of its ground state is an important issue in order to figure out the relevant mechanism driving materials into peculiar charge ordering. In this respect, the rare-earth polychalcogenides RTen (where R is the rare earth element and n=2, 2.5, 3) have recently attracted great interest because of their low dimensionality. Among the RTen families are members that variously host large commensurate distortions, ordered and disordered vacancy structures, and Fermi surface driven charge-density-wave (CDW). Optical spectroscopic methods (infrared reflectivity and Raman scattering) were applied as a function of both temperature and external pressure, in order to address the complete excitation spectrum in these CDW materials. We establish the energy scale of the single particle excitation across the CDW gap and find that the CDW collective state gaps a large portion of the Fermi surface. We discuss our optical conductivity at high frequencies with respect to predictions based on the Tomonaga-Luttinger liquid scenario. We will moreover give evidence for a coupling between the CDW condensate and the lattice vibrational modes.

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