Disorder-induced vibrational anomalies from crystalline to amorphous solids

Abstract

The origin of boson peak -- an excess of density of states over Debye's model in glassy solids -- is still under intense debate, among which some theories and experiments suggest that boson peak is related to van-Hove singularity. Here we show that boson peak and van-Hove singularity are well separated identities, by measuring the vibrational density of states of a two-dimensional granular system, where packings are tuned gradually from a crystalline, to polycrystals, and to an amorphous material. We observe a coexistence of well separated boson peak and van-Hove singularities in polycrystals, in which the van-Hove singularities gradually shift to higher frequency values while broadening their shapes and eventually disappear completely when the structural disorder $\eta$ becomes sufficiently high. By analyzing firstly the strongly disordered system ($\eta =1$) and the disordered granular crystals ($\eta =0$), and then systems of intermediate disorder with $\eta$ in between, we find that boson peak is associated with spatially uncorrelated random flucutations of shear modulus $\delta G/⟨G⟩$ whereas the smearing of van-Hove singularities is associated with spatially correlated fluctuations of shear modulus $\delta G/⟨G⟩$.

arXiv comment5 pages, 5 figures

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Cited by in corpus (6)

• Unifying description of the vibrational anomalies of amorphous materials
• Experimental observation of gapped shear waves and liquid-like to gas-like dynamical crossover in active granular matter
• Quasi-localized vibrational modes, Boson peak and sound attenuation in model mass-spring networks
• Transport and relaxation of current-generated nonequilibrium phonons from nonlocal electronic measurements
• Vibrational similarities in jamming-unjamming of polycrystalline and disordered granular packings
• Discrete holography and density of states in the crossover from hyperbolic to Euclidean lattices