Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Acoustic and optical phonon dynamics from femtosecond time-resolved
  optical spectroscopy of superconducting iron pnictide
  Ca(Fe_0.944Co_0.056)_2As_2   We report temperature evolution of coherently excited acoustic and optical
phonon dynamics in superconducting iron pnictide single crystal
Ca(Fe_0.944Co_0.056)_2As_2 across the spin density wave transition at T_SDW ~
85 K and superconducting transition at T_SC ~20 K. Strain pulse propagation
model applied to the generation of the acoustic phonons yields the temperature
dependence of the optical constants, and longitudinal and transverse sound
velocities in the temperature range of 3.1 K to 300 K. The frequency and
dephasing times of the phonons show anomalous temperature dependence below T_SC
indicating a coupling of these low energy excitations with the Cooper-pair
quasiparticles. A maximum in the amplitude of the acoustic modes at T ~ 170 is
seen, attributed to spin fluctuations and strong spin-lattice coupling before
T_SDW.

24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
17
The categories of this paper are: q-fin
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc