A crossover in spatio-temporal correlations of strain fluctuations in glass forming liquids
M. R. Hassani, M. M. Bruns, F. Varnik.
Via molecular dynamics simulations of a generic glass former in the supercooled and normal liquid states, it is shown that spatial correlations of strain fluctuations exhibit a crossover from the well-established power-law ~1/r^3-decay at long wavelengths to an exponential behavior, ~exp(-r/l_c) at intermediate distances. The characteristic length of the exponential decay grows both with temperature and time via,l_c \propto D(T)t , with D(T) being the temperature-dependent diffusion coefficient. This suggests that the crossover between the power-law and exponential decays is governed by a diffusion process.
Left panel: The spatio-temporal correlations of strain fluctuations, C_4^4(r, t) , plotted in a semi-logarithmic scale at temperature of T= 2.0 (LJ unit; T_g=0.4), evaluated for three time intervals of t=50, 100, and 200 (LJ unit). The correlations in all three time intervals depict an initial exponential decay. The size of the exponential region expands by time which could reach up to 40 particle diameters for the case of t=200 (LJ unit). Right panel: 2D spatial evolution of the correlations are shown. Even though the exponential decay extends up to 40 particle diameters, the four-fold pattern of the correlations is preserved.