Study of the phase transitions of (DI-DCNQI)_2X using vibronic and vibrational spectra

摘要

A model for the vibrational and vibronic features of the infrared spectra of a quarter-filled system is reported and shown to be able to characterise the BOW and CDW ground state of these compounds. The infrared spectra of (DI-DCNQI)_2Ag and of the corresponding compounds with Li and Cu are analysed. In particular for the Ag compound one finds that a 4k_F BOW begins to develop from room temperature and that a CDW develops below 200 K. The understanding of the periodicity of the low temperature BCDW necessitates further investigations.