The Pauli Susceptibility at a Peierls Transition

the observation of a sharp cusp in the temperature derivative of the magnetic susceptibility dx/dt is often used as a signature of a second-order structural phase transition. Such behavior is particularly prominent in low dimensional compounds undergoing a Peierls transition, where there is a large change in the density of states. We discuss how order-parameter fluctuations close to the transition lead to the observed behavior of x; the addition of impurities produces rounding of the cusp when the true phase transition is destroyed by disorder.