Fluctuation effects on the Pauli susceptibility at a Peierls transition

The observation of a sharp cusp in the temperature derivative of the magnetic susceptibility d chi /dT is often used as a signature of a second-order structural phase transition. Such behaviour is particularly prominent in low-dimensional compounds undergoing a Peierls transition, where there is a large change in the density of states. Using general arguments borrowed from magnetism, the author shows that it is short-range order parameter fluctuations close to T c that lead to the observed behaviour of chi ; the addition of impurities produces rounding of the d chi /dT cusp when the true phase transition is destroyed by disorder. The theory compares favourably with experiment.