Eq. 3 where 𝑤𝑤(𝑞𝑞) is the phonon dispersion (see supplementary information S8 for the 𝑤𝑤(𝑞𝑞) of InAs), Γ 0 is the intrinsic LO phonon linewidth, L is the crystal correlation length and q is the phonon momentum given in units of 2π/𝑎𝑎, where 𝑎𝑎 is the lattice constant (0.60583 nm for InAs).