SKM 2023 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 46: Poster: Machine Learning and Data Analytics
DY 46.11: Poster
Donnerstag, 30. März 2023, 13:00–16:00, P1
The nature of non-phononic excitations in disordered systems — •Walter Schirmacher1,2, Matteo Paoluzzi3, and Giancarlo Ruocco2,4 — 1Universität Mainz, Mainz, Germany — 2Istituto Italiano di Tecnologia, Roma, Italy — 3Universitat de Barcelona, Barcelona, Spain — 4Universita di Roma "La Sapienza", Roma, Italy
We theoretically and numerically investigate the nature of the non-phononic excitations appearing in the vibrational spectrum of disordered materials of small systems, which do not allow for low-frequency waves (phonons). Using heterogeneous-elasticity theory and a new generalization, we are able to distinguish between two types of non-phononic vibrational excitations of disordered materials (glasses). A first type (Type-I) arises beyond the boson peak due to strong scattering from the structural disorder. These excitations are similar to the eigenvectors of random matrices. In very small systems, in the absence of low-frequency waves, the spectrum exhibits a gap, which, in a marginal-stable situation, may extend to zero frequency and features a DOS proportional to the square of the frequency. In such small systems, in a more stable situation, a second type of non-phononic excitations (Type-II) appears, which involve rotational oscillations around local frozen-in stresses. The frequency spectrum of these Type-II excitations is related to the interaction potential in the regime, where the potential contributions are small, rendering the frequency dependence non-universal. The frequently observed frequency scaling with the fourth power is shown to be an artifact due to the smooth tapering of the potential cutoff in the simulations.