Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ultrafast Probes of Nonequilibrium Hole Spin Relaxation in Ferromagnetic
  Semiconductor GaMnAs   We directly measure the hole spin lifetime in ferromagnetic GaMnAs via time-
and polarization-resolved spectroscopy. Below the Curie temperature Tc, an
ultrafast photoexcitation with linearly-polarized light is shown to create a
non-equilibrium hole spin population via the dynamical polarization of holes
through p-d exchange scattering with ferromagnetically-ordered Mn spins, and we
characterize their relaxation dynamics. The observed relaxation consists of a
distinct three-step recovery : (i) femtosecond (fs) hole spin relaxation ~
$160-200 fs, (ii) picosecond (ps) hole energy relaxation ~ 1-2 ps, and (iii) a
coherent, damped Mn spin precession with a period of ~ 250 ps. The transient
amplitude of the hole spin component diminishes with increasing temperature,
directly following the ferromagnetic order, while the hole energy amplitude
shows negligible temperature change, consistent with our interpretation. Our
results thus establish the hole spin lifetimes in ferromagnetic semiconductors
and demonstrate a novel spectroscopy method for studying non-equilibrium hole
spins in the presence of correlation and magnetic order.

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The categories of this paper are: solv-int
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: plasm-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: adap-org
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The categories of this paper are: q-bio
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The categories of this paper are: patt-sol
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The categories of this paper are: funct-an
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The categories of this paper are: supr-con
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The categories of this paper are: acc-phys
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The categories of this paper are: math
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The categories of this paper are: econ
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The categories of this paper are: chem-ph
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The categories of this paper are: dg-ga