  It is a persistent problem in condensed matter physics that glasses exhibit
vibrational and thermal properties that are markedly different from those of
crystals. While recent works have advanced our understanding of vibrational
excitations in glasses at the harmonic approximation limit, efforts in
understanding finite-temperature anharmonic processes have been limited. It is
well known that phonons in crystals couple through phonon-phonon interactions,
an extremely efficient mechanism for anharmonic decay that is also important in
glasses. Here, however, we show that an additional anharmonic channel of
different origin emerges in the case of glasses, which induces intermittent
rearrangements of particles. We have found that thermal vibrations in glasses
trigger transitions among numerous different local minima of the energy
landscape, which, however, are located within the same wide (meta)basin. These
processes generate motions that are different from both diffusive and
out-of-equilibrium aging dynamics. We suggest that the intermittent
rearrangements accompanying thermal fluctuations are crucial features
distinguishing glasses from crystals.
