757 research outputs found
Towards a Banking Union: Open Issues. Bruges European Economic Policy (BEEP) Briefing 32/2014
No abstract
Structure factors of harmonic and anharmonic Fibonacci chains by molecular dynamics simulations
The dynamics of quasicrystals is characterized by the existence of phason
excitations in addition to the usual phonon modes. In order to investigate
their interplay on an elementary level we resort to various one-dimensional
model systems. The main observables are the static, the incoherent, and the
coherent structure factor, which are extracted from molecular dynamics
simulations. For the validation of the algorithms, results for the harmonic
periodic chain are presented. We then study the Fibonacci chain with harmonic
and anharmonic interaction potentials. In the dynamic Fibonacci chain
neighboring atoms interact by double-well potentials allowing for phason flips.
The difference between the structure factors of the dynamic and the harmonic
Fibonacci chain lies in the temperature dependence of the phonon line width. If
a bias is introduced in the well depth, dispersionless optic phonon bands split
off.Comment: 12 pages, 15 figure
Interpretation of some Yb-based valence-fluctuating crystals as approximants to a dodecagonal quasicrystal
The hexagonal ZrNiAl-type (space group: P-62m) and the tetragonal
Mo2FeB2-type (space group: P4/mbm) structures, which are frequently formed in
the same Yb-based alloys and exhibit physical properties related to
valence-fluctuation, can be regarded as approximants of a hypothetical
dodecagonal quasicrystal. Using Pd-Sn-Yb system as an example, a model of
quasicrystal structure has been constructed, of which 5-dimensional crystal
(space group: P12/mmm, aDD=5.66 {\AA} and c=3.72 {\AA}) consists of four types
of acceptance regions located at the following crystallographic sites; Yb
[00000], Pd[1/3 0 1/3 0 1/2], Pd[1/3 1/3 1/3 1/3 0] and Sn[1/2 00 1/2 1/2]. In
the 3-dimensional space, the quasicrystal is composed of three types of
columns, of which c-projections correspond to a square, an equilateral triangle
and a 3-fold hexagon. They are fragments of two known crystals, the hexagonal
{\alpha}-YbPdSn and the tetragonal Yb2Pd2Sn structures. The model of the
hypothetical quasicrystal may be applicable as a platform to treat in a unified
manner the heavy fermion properties in the two types of Yb-based crystals.Comment: 19 pages, 6 figure
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