Non-equilibrium electronic Grüneisen parameter

Abstract

The electronic Gruneisen parameter, γe, is a fundamental parameter characterizing the relationship between thermal expansion and electronic specific heat. Conventionally, γe is measured at low temperatures for minimizing the lattice contribution to thermal expansion. In this paper, we extract γe by separating the electron and lattice contributions in time domain using ultrashort pulse excitation. We show that γe cannot be considered as a constant during the electron-lattice thermal nonequilibrium state. Instead, a revised expression for γe is proposed for the non-equilibrium electron–phonon system.