Atomic theory of viscoelastic response and memory effects in metallic glasses

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Yang, J 
Qiao, J 
Jiang, M 
Dai, L 

An atomic-scale theory of the viscoelastic response of metallic glasses is derived from first principles, using a Zwanzig-Caldeira-Leggett system-bath Hamiltonian as a starting point within the framework of nonaffine linear response to mechanical deformation. This approach provides a generalized Langevin equation (GLE) as the average equation of motion for an atom or ion in the material, from which non-Markovian nonaffine viscoelastic moduli are extracted. These can be evaluated using the vibrational density of states (DOS) as input, where the boson peak plays a prominent role in the mechanics. To compare with experimental data for binary ZrCu alloys, a numerical DOS was obtained from simulations of this system, which also take electronic degrees of freedom into account via the embedded-atom method for the interatomic potential. It is shown that the viscoelastic α-relaxation, including the α-wing asymmetry in the loss modulus, can be very well described by the theory if the memory kernel (the non-Markovian friction) in the GLE is taken to be a stretched-exponential decaying function of time. This finding directly implies strong memory effects in the atomic-scale dynamics and suggests that the α-relaxation time is related to the characteristic time scale over which atoms retain memory of their previous collision history.

cond-mat.soft, cond-mat.soft, cond-mat.dis-nn, cond-mat.mtrl-sci, cond-mat.other, cond-mat.stat-mech
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Physical Review B - Condensed Matter and Materials Physics
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