title: The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors.
abstract: In the underdoped copper-oxides, high-temperature superconductivity condenses 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. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders 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, τqp, as a function of temperature and magnetic field in underdoped HgBa2CuO(4+δ) (Hg-1201) and YBa2Cu3O(6+x) (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T) exhibits a local maximum in a small temperature window near Tc 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 Tc 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.
authors.affiliation: Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Department of Physics, University of California, Berkeley, California 94720, USA.|Department of Physics, University of California, San Diego, California 92093, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Hinton
authors.affiliation: Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: E
authors.initials: E
authors.lastname: Thewalt
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Alpichshev
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: F
authors.initials: F
authors.lastname: Mahmood
authors.affiliation: Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Koralek
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Chan
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Veit
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Dorow
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.|Institute of Solid State Physics, TU Wien, 1040 Vienna, Austria.
authors.forename: N
authors.initials: N
authors.lastname: Barišić
authors.affiliation: Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Department of Physics, North Carolina State University, Raleigh, North Carolina 27695-7518, USA.
authors.forename: A F
authors.initials: AF
authors.lastname: Kemper
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada.|Canadian Inst. Adv. Res., Toronto, ON M5G 178, Canada.
authors.forename: D A
authors.initials: DA
authors.lastname: Bonn
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada.|Canadian Inst. Adv. Res., Toronto, ON M5G 178, Canada.
authors.forename: W N
authors.initials: WN
authors.lastname: Hardy
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada.|Canadian Inst. Adv. Res., Toronto, ON M5G 178, Canada.
authors.forename: Ruixing
authors.initials: R
authors.lastname: Liang
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: N
authors.initials: N
authors.lastname: Gedik
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: M
authors.initials: M
authors.lastname: Greven
authors.affiliation: Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: A
authors.initials: A
authors.lastname: Lanzara
authors.affiliation: Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.|Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: J
authors.initials: J
authors.lastname: Orenstein