Light-Induced Giant Softening of Network Glasses Observed near the Mean-Field Rigidity Transition

摘要

The longitudinal acoustic (LA) mode of bulk Ge_xSe_(1-x) glasses is examined in Brillouin scattering (BS) over the 0.15 < x < 1/3 range using near band-gap radiation (λ = 647.1 nm). The LA-mode frequency (v_(LA) softens with increasing laser power in an athermal and reversible manner by nearly 30% ( = Δv_(LA)/v_(LA)) near x = x_c = 0.19(1) or mean coordination number, r_c = 2 + 2x_c = 2.38(2), close to the mean-field rigidity percolation transition (r_t = 2.40). BS is a bulk probe of elasticity, and photosoftening is maximized here when network stress is minimized near the elastic phase transition.