1,129 research outputs found
Heterogeneity in structurally arrested hard spheres
When cooled or compressed sufficiently rapidly, a liquid vitrifies into a glassy amorphous state. Vitrification in a dense liquid is associated with jamming of the particles. For hard spheres, the density and degree of order in the final structure depend on the compression rate: simple intuition suggests, and previous computer simulation demonstrates, that slower compression results in states that are both denser and more ordered. In this work, we use the Lubachevsky-Stillinger algorithm to generate a sequence of structurally arrested hard-sphere states by varying the compression rate. We find that while the degree of order, as measured by both bond-orientation and translation order parameters, increases monotonically with decreasing compression rate, the density of the arrested state first increases, then decreases, then increases again, as the compression rate decreases, showing a minimum at an intermediate compression rate. Examination of the distribution of the local order parameters and the distribution of the root-mean-square fluctuation of the particle positions, as well as direct visual inspection of the arrested structures, reveal that they are structurally heterogeneous, consisting of disordered, amorphous regions and locally ordered crystal-like domains. In particular, the low-density arrested states correspond with many interconnected small crystal clusters that form a polycrystalline network interspersed in an amorphous background, suggesting that jamming by the domains may be an important mechanism for these states
High-order harmonic generations in tilted Weyl semimetals
We investigate high-order harmonic generations (HHGs) under the comparison of
Weyl cones in two types. Due to the hyperboloidal electron pocket structure,
strong noncentrosymmetrical generations in high orders are observed around a
single type-II Weyl point, especially at frequency zero. Such remarkable DC
signal is proved to have attributions from the intraband transition after
spectral decomposition. Under weak pulse electric field , the linear optical
response of a non-tilted Weyl cone is consistent with the Kubo theory. With
more numerical simulations, we conclude the non-zero chemical potential can
enhance the even-order generations, from the slightly tilted system to the
over-tilted systems. In consideration of dynamical symmetries, type-I and -II
Weyl cones also show different selective responses under the circularly
polarized light. Finally, using a more realistic model containing two pairs of
Weyl points, we demonstrate the paired Weyl points with opposite chirality
could suppress the overall even-order generations
Thermodynamics of the Mg-B system: Implications for the deposition of MgB2 thin films
We have studied thermodynamics of the Mg-B system with the modeling technique
CALPHAD using a computerized optimization procedure. Temperature-composition,
pressure-composition, and pressure-temperature phase diagrams under different
conditions are obtained. The results provide helpful insights into appropriate
processing conditions for thin films of the superconducting phase, MgB2,
including the identification of the pressure/temperature region for
adsorption-controlled growth. Due to the high volatility of Mg, MgB2 is
thermodynamically stable only under fairly high Mg overpressures for likely
growth temperatures. This constraint places severe temperature constraints on
deposition techniques employing high vacuum conditions
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