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Rotter, L. D.; Schlesinger, Z.; Collins, R. T.; Holtzberg, F.; Field, C.; Welp, U.; Crabtree, G. W.; Liu, J. Z.; Fang, Y.; Vandervoort, K. G.; Fleshler, S.

doi:10.1103/physrevlett.67.2741

Cited by 212 publications

(77 citation statements)

References 18 publications

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“…As emphasized in Ref. [4], the increase of DR͞R with decreasing T tracks the growth of a spin resonance peak seen by neutron scattering [5,6] and a gaplike feature seen in optical conductivity [7,8]. Furthermore, DR͞R shows the same behavior with varying carrier concentration as do these spectroscopic features, namely abrupt onset at T c for near optimal doping [9] and a slow onset above T c for underdoped materials [1,4].…”

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confidence: 67%

Photoinduced Changes of Reflectivity in Single Crystals ofYBa2Cu3O6.5(Or

et al. 2002

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We report measurements of the photoinduced change in reflectivity of an untwinned single crystal of YBa 2 Cu 3 O 6.5 in the ortho II structure. The decay rate of the transient change in reflectivity is found to decrease rapidly with decreasing temperature and, below T c , with decreasing laser intensity. We interpret the decay as a process of thermalization of antinodal quasiparticles, with a rate determined by inelastic scattering of quasiparticle pairs. DOI: 10.1103/PhysRevLett.88.137001 PACS numbers: 74.25.Gz, 78.47. +p The desire to understand the pseudogap phenomenon continues to dominate research in the high-T c cuprates. At issue is the nature of the partial gap that onsets well above T c in underdoped materials. The gap is likely to be a manifestation of either fluctuating or long-range order. A key question is whether this order competes with or enhances superconductivity, or is, in fact, a fluctuating form of the superconducting phase itself.One approach to answering this question is to study the dynamics of nonequilibrium quasiparticles, which can be extremely sensitive to a gap [1,2]. A promising technique to study such dynamics is optical pump and probe spectroscopy. In this type of experiment a pulse of light stimulates a nonequilibrium state with excess energy and quasiparticle density. A weaker pulse, which is delayed relative to the pump, probes the nonequilibrium state by detecting changes in the absorptance or reflectance. Dynamics can be measured with subpicosecond time resolution while anisotropy can be explored by varying the polarization of the pump and probe beams.In this paper we report pump and probe measurements performed on an untwinned single crystal of YBa 2 Cu 3 O 6.5 (Ortho II). Together with YBa 2 Cu 4 O 8 it is one of two underdoped materials in which doping does not introduce disorder. We find, in contrast with an earlier report [3] on underdoped films, that the decay rate of the photoinduced change in reflectivity, DR͞R, depends strongly on the excitation density and temperature. Because it vanishes in the limit that both tend to zero, we interpret the decay rate as an inelastic scattering rate of quasiparticle pairs. We present evidence that the decay corresponds to a process of thermalization, rather than recombination, of the nonequilibrium quasiparticle population. The dynamics of thermalization change suddenly upon crossing from the pseudogap regime to the superconducting state.We measured the decay of the DR͞R at a photon energy of 1.5 eV due to excitation with photons of the same energy. The optical pulses are produced by a mode-locked Ti:sapphire laser, and have duration 100 fs, pulse to pulse separation 12 ns, and center wavelength 800 nm. Both the pump and probe beams were focused onto the sample with a 20 cm focal length lens, yielding a spot size with 90% of its intensity within a 100 mm diameter. A photoelastic modulator varied the pump intensity at 100 kHz and a vibrating mirror oscillating at 40 Hz varied the time delay between pump and probe. This double mo...

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confidence: 67%

Photoinduced Changes of Reflectivity in Single Crystals ofYBa2Cu3O6.5(Or

et al. 2002

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“…Hamiltonian (2) and from the fermions that we integrated out but the latter is always small in parameter T c /ǫ F leading to a simple result, γ ′′ = −1. Action of a generic form (7) but with different parameter values describes also usual BCS type superconductivity in the Fermi liquid, bose condesation and interpolation between these two regimes [14].…”

Section: Modelmentioning

confidence: 99%

“…It is known for a long time that excitation spectrum in underdoped high T c cuprates shows formation of the pseudogap at temperature T s far above T c ; this phenomena was observed in the NMR responses [1] and in optics [2][3][4]. Recently the photoemission experiments showed that this phenomena can be attributed to the electrons in the corners of the Fermi surface which acquire a gap in these materials at about the same temperature at which pseudogap is observed in optics and NMR [5].…”

Section: Introductionmentioning

confidence: 99%

Superconductivity in a system with preformed pairs

1997

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We discuss the phenomenology of the superconductivity resulting from the bose condensation of the preformed pairs coexisting with unpaired fermions. We show that this transition is more mean field like than usual bose condensation, i.e. it is characterized by a relatively small value of the Ginzburg parameter. We consider the Hall effect in the vortex flow regime and in the fluctuational regime above Tc and show that in this situation it is much less than in the transition driven entirely by bose condesation but much larger than in a usual superconductivity. We analyse the available Hall data and conclude that this phenomenology describes reasonably well the data in the underdoped materials of Y BaCuO family but is not an appropriate description of optimally doped materials or underdoped LaSrCuO.

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“…The hump structure is largely originated from the amplitude fluctuations of the η mode. Both the U(1) and SU (2) showed that the hump is originated from the antiferromagnetic spin fluctuations of short range order, although we cannot deduce separate contributions from the two different amplitude(|χ| and |∆ f |) fluctuations in this SU(2) calculation. This is because the amplitude fluctuations of both hopping order and spin(spinon) pairing order parameters occur in the background of antiferromagnetic fluctuations.…”

Section: B Optical Conductivity In U(1) and Su(2) Slave-boson Theoriesmentioning

confidence: 99%

“…This strong correlation results in the peak-dip-hump structure of the optical conductivity σ(ω) and linear frequency dependence of the scattering rate 1/τ (ω) [1][2][3][4][5][6]. Both the appearance of the hump(which occurs at ω ≈ 1000cm −1 in YBCO [3,4] and Bi2212 [6]) and the linear frequency dependence of the scattering rate(1/τ (ω) ∼ ω) indicate strong deviations from the Drude model prediction of conventional Fermi-liquid.…”

Section: Introductionmentioning

confidence: 99%

Origin of the hump structure in the in-plane optical conductivity of high-TCcuprates based on aSU(2)slave-boson theory

et al. 2004

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An improved version of SU(2) slave-boson approach is applied to study the in-plane optical conductivity of the two dimensional systems of high TC cuprates. We investigate the role of fluctuations of both the phase and amplitude of order parameters on the (Drude) peak-dip-hump structure in the in-plane conductivity as a function of hole doping concentration and temperature. The mid-infrared(MIR) hump in the in-plane optical conductivity is shown to originate from the antiferromagnetic spin fluctuations of short range(the amplitude fluctuations of spin singlet pairing order parameters), which is consistent with our previous U(1) study. However the inclusion of both the phase and amplitude fluctuations is shown to substantially improve the qualitative feature of the optical conductivity by showing substantially reduced Drude peak widths for entire doping range. Both the shift of the hump position to lower frequency and the growth of the hump peak height with increasing hole concentration is shown to be consistent with observations.

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Dependence of the infrared properties of single-domainYBa2Cu3

Cited by 212 publications

References 18 publications

Photoinduced Changes of Reflectivity in Single Crystals ofYBa2Cu3O6.5(Or

Photoinduced Changes of Reflectivity in Single Crystals ofYBa2Cu3O6.5(Or

Superconductivity in a system with preformed pairs

Origin of the hump structure in the in-plane optical conductivity of high-TCcuprates based on aSU(2)slave-boson theory

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