Generalized hydrodynamics of binary liquids: transverse collective modes

Area of Science:

• Condensed Matter Physics
• Statistical Mechanics
• Materials Science

Background:

• Understanding liquid dynamics beyond the hydrodynamic region is crucial for materials science.
• Lennard-Jones potential models are widely used for simulating noble gas liquids like Kr-Ar.
• Collective modes govern the dynamic properties of liquids.

Purpose of the Study:

• To investigate the transverse dynamics of liquid Kr-Ar using a parameter-free generalized collective modes approach.
• To identify and characterize propagating eigenmodes in the transverse collective excitation spectrum.
• To analyze the behavior of these modes in different wave number regimes (hydrodynamic vs. beyond).

Main Methods:

• Application of the parameter-free generalized collective modes approach.
• Utilizing an eight-variable approximation for dynamical variables.
• Analysis of time correlation functions and spectral functions.
• Investigation using different basis sets of dynamical variables.

Main Results:

• Identification of four branches of propagating eigenmodes in the transverse collective excitation spectrum.
• Demonstration of a transition from 'partial' character at large wave numbers to collective liquid behavior in the hydrodynamic limit.
• Derivation of the condition for the existence of high-frequency mass-concentration waves.
• Observation that high-frequency excitations resemble optic phonon modes in solids.

Conclusions:

• The generalized collective modes approach effectively describes transverse dynamics in liquid Kr-Ar.
• Transverse excitations exhibit distinct behaviors depending on the wave number regime.
• High-frequency collective excitations are linked to mass-concentration fluctuations and exhibit solid-like phonon properties.