Quantum thermal transport in glasses: the role of anharmonicity

Thermal transport in glasses is often described by the harmonic theory introduced by Allen and Feldman [Phys. Rev. Lett., 62(6) (1989)], where heat is carried by couplings between vibrational modes and disorder limits the thermal conductivity. Hitherto, the effects of anharmonicity on heat conduction in glasses have been investigated using molecular simulations, combined with empirical quantum corrections to address discrepancies with experiments at low temperature. Recently, a unified theory of thermal transport in crystals and glasses has been formulated [Simoncelli, Marzari, and Mauri, Nat. Phys., 15 (2019)], allowing to account rigorously for quantum and anharmonic effects also in glassy or disordered systems. Here, we show that quantum effects and anharmonicity are crucial to explain the increasing non-saturating trend of the thermal conductivity with temperature observed in silica glass --- and not explained by the saturating Allen-Feldman harmonic theory. We analyze amorphous silica as a prototypical glass and provide recipes to perform first-principles quantum thermal conductivity calculations in glasses, which are accurate over a wide temperature range.