Inversion symmetric vs. asymmetric excitations and the low-temperature universal properties of Ar:N2 and Ar:N2:CO glassesA. Gaita-Ariño, V. F. González-Albuixech and M. SchechterEPL, 109 5 (2015) 56001DOI: https://doi.org/10.1209/0295-5075/109/56001