Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Crystallization of self-propelled hard-discs : a new scenario   We experimentally study the crystallization of a monolayer of vibrated discs
with a built-in polar asymmetry, a model system of active liquids, and contrast
it with that of vibrated isotropic discs. Increasing the packing fraction
$\phi$, the quasi-continuous crystallization reported for isotropic discs is
replaced by a transition, or a crossover towards a "self-melting" crystal.
Increasing the packing fraction from the liquid phase, clusters of dense
hexagonally-ordered packed discs spontaneously form, melt, split and merge
leading to a highly intermittent and heterogeneous dynamics. The resulting
steady state cluster size distribution decreases monotonically. For packing
fraction larger than $\phi^*$, a few large clusters span the system size and
the cluster size distribution becomes non monotonic, the transition being
signed by a power-law. The system is however never dynamically arrested. The
clusters permanently melt from place to place forming droplets of active liquid
which rapidly propagate across the system. This state of affair remains up to
the highest possible packing fraction questioning the stability of the crystal
for active discs, unless at ordered close packing.

12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol