Ferroelastic fluctuations in high-temperature superconductors

It is shown that the specific heat jump at the superconducting transition temperature in pnictide and cuprate superconductors is produced by ferroelastic fluctuations just below the transition temperature. The amplitude of the corresponding lattice distortion is estimated. It is shown that a contribution from ferroelastic fluctuations to the specific heat jump is also present in low-temperature superconductors.