Multimode Peierls distortion in triangular lattice

Abstract

We have studied the multimode Peierls states in the electron–lattice system on a triangular lattice with a three‐quarter‐filled electronic band. Below the transition temperature, we have found many stable states of nearly same free‐energy. Focusing our attention on the lowest free‐energy state, we have found that the Peierls order parameter continuously increases from zero just below the transition temperature. When the temperature is raised from the region lower than the critical temperature, multiple phonon modes are simultaneously softened at the same temperature as when the temperature is lowered from the region higher that the critical temperature. These results tell us that the transition is of the second order. The non‐softened modes are also found to condense due to nonlinear coupling between the non‐softened modes and the softened modes. The degeneracy of the phonon modes observed at the higher temperature region is partially lifted at the lower temperature region.