Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Phonon hydrodynamics and ultrahigh-room-temperature thermal conductivity
  in thin graphite   Allotropes of carbon, such as diamond and graphene, are among the best
conductors of heat. We monitored the evolution of thermal conductivity in thin
graphite as a function of temperature and thickness and found an intimate link
between high conductivity, thickness, and phonon hydrodynamics. The room
temperature in-plane thermal conductivity of 8.5-micrometer-thick graphite was
4300 watts per meter-kelvin-a value well above that for diamond and slightly
larger than in isotopically purified graphene. Warming enhances thermal
diffusivity across a wide temperature range, supporting partially hydrodynamic
phonon flow. The enhancement of thermal conductivity that we observed with
decreasing thickness points to a correlation between the out-of-plane momentum
of phonons and the fraction of momentum relaxing collisions. We argue that this
is due to the extreme phonon dispersion anisotropy in graphite.

15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
10
The categories of this paper are: q-bio
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat