Evidence for two-level states and cooperative atomic jumps in a computer model of amorphous Ni81B19

Following a new approach we study the atomic motion associated with double-well potential energy minima, whose existence in non-crystalline matter has been predicted by the two-level states theory. These minima are located at the same sites as low-frequency localized vibrational modes and the ‘launching’ of such a mode can result in a jump into a new potential energy minimum. The jump has a cooperative character involving some tens of atoms. The potential energy changes during a jump indicate that the new local configuration is only stable because the displacement of all atoms involved creates a new potential energy minimum, rather than that the atoms move into an already existent neighboring potential minimum. The significance of this type of jumps for diffusion is discussed.