Condensed Matter Physics Seminar: Lorenzo Caprini

Abstract

Entropy production has been introduced in the 19th century to describe the amount of irreversibility in thermodynamic cycles and is behind the formulation of the second law of thermodynamics. It represents a fundamental concept in Physics and beyond that has been recently linked to microscopic dynamics to quantify irreversibility and dissipation at the atomistic level. Here, we study the entropy production in crystals across different length scales. At the microscopic scale, we calculate the ultrafast entropy production of a crystal excited by a THz laser pulse, by starting from the dynamics of an optical phonon mode. The entropy is measured from ionic displacements, obtained from time-resolved X-ray scattering experiments, and linked to the power spectrum of the crystal. At larger length scales, we analyze the entropy production of solids formed by soft particles, such as active colloids, cells, and active granulars, that are intrinsically out of equilibrium also in the absence of an external force. In this case, the entropy production generates additional vibrational excitations that we name "entropons" because they represent modes of the spectral entropy production. Entropons coexist with conventional phonons with thermal origin and dominate over them when the system is far from equilibrium.