Percolation dissipation of the α and β processes in metallic glasses.

Dynamic processes in glasses are crucial for unraveling the fundamentals of glass transition and material properties. A recent theoretical framework proposes a unified "doublepercolation" scenario for the α and β relaxation processes. While supported by simulations, no experimental validation has so far been presented. We here conduct a comprehensive analysis of the relaxation dissipation of more than 300 mechanical spectra of metallic glass samples. Our study yields two key findings, both aligning with the double percolation theory: (i) The α relaxation has a damping factor of 0.6 (± 0.05), independent of material composition, probing frequency, and thermal history -a signature that is consistent with the percolation of immobile atomic clusters proposed to characterize the α relaxation. (ii) The β relaxation dissipation, though of variable magnitude and dependent on external factors, can be rationalized as caused by the percolation of mobile atomic entities driving configurational rearrangements; thus for the β relaxation we show that certain atomic motions are neither dissipative nor induce configurational changes. These results bridge theoretical predictions with experimental observations, suggesting a generally applicable picture of the atomic-scale mechanisms of relaxation dissipation in glass formers.