Internally Stressed and Positionally Disordered Minimal Complexes Yield Glasslike Nonphononic Excitations

Area of Science:

• Condensed matter physics
• Materials science
• Statistical mechanics

Background:

• Glasses exhibit unique low-frequency nonphononic excitations with a universal D(ω)∼ω⁴ density of states.
• Understanding the origins of these excitations is challenging due to the interplay of positional disorder and mechanical frustration in glass formation.

Purpose of the Study:

• To identify the minimal physical ingredients responsible for generating glasslike excitations in amorphous solids.
• To investigate the roles of mechanical frustration and positional disorder in vibrational spectra.

Main Methods:

• Analysis of vibrational spectra of isolated minimal complexes.
• Computational modeling of ensembles of minimal complexes.
• Embedding single minimal complexes within perfect lattices.

Main Results:

• Minimal complexes, characterized by mechanical frustration and positional disorder, were identified as key structural motifs.
• Ensembles of marginally stable minimal complexes were shown to produce the universal D(ω)∼ω⁴ density of states.
• The emergence of glasslike excitations was demonstrated by incorporating minimal complexes into crystalline lattices.

Conclusions:

• Minimal complexes provide a fundamental, first-principles framework for understanding glasslike excitations.
• This work offers a practical computational approach for introducing glasslike excitations into solid materials.