Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Structural Origin of Boson Peak in Glasses   Boson peak, the excess low energy excitations in the terahertz regime, is one
of the most unique features of disordered systems and has been linked to many
anomalous properties of glass materials. The nature and structural origin of
the boson peak remain elusive and have been debated for more than a half
century mainly due to the lack of real-time and real-space experimental
insights of the dynamic phenomenon. In this work we employed femtosecond MeV
ultrafast electron diffraction to characterize the atomic dynamics of metallic
glasses in real time. The experiment reveals collective atomic oscillations,
presented in elastic electron scattering and atomic pair distribution
functions, within the boson peak frequency range of 1.0-1.8 THz in both
reciprocal and real space. It was found that the oscillation frequency has
reciprocal dependence on interatomic pair distances and the corresponding wave
velocity experimentally affirms the transverse acoustic wave nature of the
boson peak. The observed strong correlation between THz acoustic vibrations and
coherent electron scattering provides compelling evidence that the boson peak
originates from the collective transverse vibrational modes of structurally
ordered atoms in the disordered system.

2
The categories of this paper are: math
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex