Modulational Instability of Delocalized Modes in fcc Copper

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nonlinear Dynamics

Background:

• Delocalized nonlinear vibrational modes (DNVMs) are exact solutions to equations of motion, existing at any amplitude.
• DNVMs are independent of specific interaction potentials, making them broadly applicable.
• Understanding vibrational modes is crucial for predicting material properties under various conditions.

Purpose of the Study:

• To investigate the modulation instability of four one-component, three-dimensional DNVMs in fcc copper.
• To analyze the impact of DNVMs on crystal properties like frequency, stress, energy, and heat capacity.
• To characterize the resulting discrete breathers (DBs) and their behavior.

Main Methods:

• Molecular dynamics simulations were employed to study DNVMs.
• Analysis included DNVMs frequencies, stress evolution, kinetic and potential energies.
• Heat capacity was examined as a function of oscillation amplitudes.

Main Results:

• All four studied DNVMs exhibit hard-type anharmonicity.
• Modulation instability leads to the formation of chaotic discrete breathers (DBs) with frequencies above the phonon spectrum.
• Chaotic DBs have lifetimes of 30-100 ps, with longer lifetimes at lower oscillation frequencies.
• Increased modulation instability raises mechanical stresses and lowers heat capacity.

Conclusions:

• Modulation instability of DNVMs is a key factor influencing the properties of metals.
• The formation of chaotic DBs alters the vibrational landscape and thermodynamic properties.
• This research enhances the understanding of nonlinear dynamics in crystalline solids.