Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The rate of quasiparticle recombination probes the onset of coherence in
  cuprate superconductors   The condensation of an electron superfluid from a conventional metallic state
at a critical temperature $T_c$ is described well by the BCS theory. In the
underdoped copper-oxides, high-temperature superconductivity condenses instead
from a nonconventional metallic "pseudogap" phase that exhibits a variety of
non-Fermi liquid properties. Recently, it has become clear that a charge
density wave (CDW) phase exists within the pseudogap regime, appearing at a
temperature $T_{CDW}$ just above $T_c$. The near coincidence of $T_c$ and
$T_{CDW}$, as well the coexistence and competition of CDW and superconducting
order below $T_c$, suggests that they are intimately related. Here we show that
the condensation of the superfluid from this unconventional precursor is
reflected in deviations from the predictions of BSC theory regarding the
recombination rate of quasiparticles. We report a detailed investigation of the
quasiparticle (QP) recombination lifetime, $\tau_{qp}$, as a function of
temperature and magnetic field in underdoped HgBa$_{2}$CuO$_{4+\delta}$
(Hg-1201) and YBa$_{2}$Cu$_{3}$O$_{6+x}$ (YBCO) single crystals by ultrafast
time-resolved reflectivity. We find that $\tau_{qp}(T)$ exhibits a local
maximum in a small temperature window near $T_c$ that is prominent in
underdoped samples with coexisting charge order and vanishes with application
of a small magnetic field. We explain this unusual, non-BCS behavior by
positing that $T_c$ marks a transition from phase-fluctuating SC/CDW composite
order above to a SC/CDW condensate below. Our results suggest that the
superfluid in underdoped cuprates is a condensate of coherently-mixed
particle-particle and particle-hole pairs.

2
The categories of this paper are: math
1
The categories of this paper are: cs
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom
17
The categories of this paper are: q-fin
30
The categories of this paper are: q-alg