X-Ray Study of the Density Wave Instability of alpha-(BEDT-TTF)2MHg(SCN)4 with M=K and Rb

TL;DR

This study uses X-ray diffraction to investigate density wave phase transitions in quasi-2D conductors, revealing incommensurate modulations and their coupling with electronic properties, indicating charge density wave formation.

Contribution

It provides detailed structural insights into the density wave transition in alpha-(BEDT-TTF)2MHg(SCN)4 compounds, highlighting the incommensurate modulation and its electronic coupling.

Findings

Presence of satellite reflections at ambient temperature

Incommensurate modulation with multiple harmonics

Strong increase in satellite reflection intensity below transition temperature

Abstract

We present an X-ray diffraction study of the quasi-2D conductors a-(BEDTTTF)2MHg(SCN), with M=K and Rb. They exhibit a phase transition of the density wave type at TDW=8-10K and 12-13K respectively, evidenced by magnetoresistivity, specific heat, NMR and Hall constant measurements. The structural study shows the presence of satellite reflections already at ambient temperature. The related modulation is incommensurate with multiple harmonics. For some of the compounds studied, the intensity of the satellite reflections strongly increases below TDW. According to Fermi surface (FS) calculations, the wave vector of the structural modulation achieves a quite good nesting of the global FS. This suggests a coupling of the modulation with the electronic degrees of freedom leading to a charge density wave ground state.