reprinted from Festkorperprobleme/Adv. in Solid State Physics 38 425{437 (1999) A New Look at Low{Temperature Anomalies in Glasses

Abstract: We review a model{based rather than phenomenological approach to low{temperature anomalies in glasses. Specically, we present a solvable model inspired by spin{glass theory that exhibits both, a glassy low{temperature phase, and a collection of double { and single{well congurations in its poten-tial energy landscape. The distribution of parameters characterizing the local potential energy congurations can be computed, and is found to dier from those assumed in the standard tunneling model and its variants. Still, low tem-perature anomalies characteristic of amorphous materials are reproduced. More importantly perhaps, we obtain a clue to the universality issue. That is, we are able to distinguish between properties which can be expected to be universal and those which cannot. Our theory also predicts the existence, under suitable circumstances of amorphous phases without low{energy tunneling excitations. Dedicated to Heinz Horner on the occasion of his 60 th birthday.