Gap ratio in anharmonic charge-density-wave systems

Abstract

Many experimental systems exist that possess charge-density-wave order in their ground state. While this order should be able to be described with models similar to those used for superconductivity, nearly all systems have a ratio of the charge-density-wave order parameter to the transition temperature that is too high for conventional theories. Recent work explained how this can happen in harmonic systems, but when the lattice distortion gets large, anharmonic effects must play an increasingly important role. Here we study the gap ratio for anharmonic charge-density wave systems to see whether the low-temperature properties possess universality as was seen previously in the transition temperature and to see whether the explanation for the large gap ratios survives for anharmonic systems as well.