Temperature dependent phonon dynamics in the quasi-one-dimensional systems

The dynamical properties of phonons coupled linearly to the electrons with a planar Fermi surface, are examined at finite temperature. The additional phonon branch, found previously from the T = 0 calculations, should not be observable in the Nb₃Sn-like compounds, which undergo the cubic-to-tetragonal transition. This additional branch exists however in the weak coupling limit, where, unexpectedly, the soft mode becomes well defined only close to the transition temperature for the Peierls instability