| Summary: | Various aspects of the tunneling states problem in metallic glasses are examined. As a first step, a computer model based on the analogy between local environments in crystalline and amorphous states is developed and used to generate and relax structures for two specific materials, namely Ni(,80)P(,20) and Cu(,33)Zr(,67). The model is found to give a physically realistic picture of the systems examined, in particular by properly accounting for short-range order effects. The structures are then analyzed in terms of single-atom tunneling taking place between two metastable minimum-energy positions. The probability of occurence of such "two-level systems" (TLS's) is shown to be strongly correlated with the degree of relaxation and thus with the density of the system. Further, they are seen to be associated with voids in the structure which disappear upon relaxation, suggesting an analogy with the physical process of annealing metallic glasses below their glass transition temperatures. It is therefore concluded that a reduction of the various low-temperature anomalies in these materials should result from the annealing process. As a verification, the change in superconducting transition temperature T(,c) due to the presence of TLS's is evaluated. In leading to a non-negligible enhancement effect, our model is indeed found to provide a reasonable estimate of the observed drop in T(,c), thus corroborating our hypothesis of a reduction of the TLS density of states upon thermal relaxation.
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