Nonequilibrium superconductivity and quasiparticle dynamics in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">YBa</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow>

Averitt, R. D.; Rodriguez, George; Lobad, A. I.; Siders, Jennifer L. W.; Trugman, S. A.; Taylor, Antoinette J.

doi:10.1103/physrevb.63.140502

Cited by 119 publications

(106 citation statements)

References 23 publications

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“…One of the central observations, and possibly the most puzzling, has been the behavior of the quasiparticle recombination rate, , as a function of temperature, T, and photoinjected density, n ph . Two classes of behavior are found: in class (1) appears to vanish as T [2 -6] and n ph [2,5,7,8] tend to zero, while in class (2) remains essentially constant with decreasing T [9][10][11] and n ph [12]. Another, seemingly distinct, puzzle concerns the sign of the photoinduced change in sample reflectivity, R, which can be either positive or negative [2,9,[13][14][15].…”

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confidence: 99%

Abrupt Transition in Quasiparticle Dynamics at Optimal Doping in a Cuprate Superconductor System

et al. 2005

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We report time-resolved measurements of the photoinduced change in reflectivity, R, in the Bi 2 Sr 2 Ca 1ÿy Dy y Cu 2 O 8 (BSCCO) system of cuprate superconductors as a function of hole concentration. We find that the kinetics of quasiparticle decay and the sign of R both change abruptly where the superconducting transition temperature T c is maximal. These coincident changes suggest that a sharp transition in quasiparticle dynamics takes place precisely at optimal doping in the BSCCO system. DOI: 10.1103/PhysRevLett.95.117005 PACS numbers: 74.25.Gz, 78.47.+p Pump and probe methods in optical spectroscopy have opened a new window on the properties of quasiparticles in cuprate superconductors and other highly correlated electron systems [1]. In experiments based on these methods, ultrashort pump pulses inject quasiparticles at densities that are continuously variable from well above to well below the thermal equilibrium level. Time-delayed probe pulses measure changes in the reflectivity or transmissivity that result from the presence of nonequilibrium quasiparticles, providing information about their recombination rates, transport, and optical properties. These studies have been carried out extensively in the cuprate superconductors, yielding a rich, complex, yet poorly understood array of experimental observations. One of the central observations, and possibly the most puzzling, has been the behavior of the quasiparticle recombination rate, , as a function of temperature, T, and photoinjected density, n ph . Two classes of behavior are found: in class (1) appears to vanish as T [2 -6] and n ph [2,5,7,8] tend to zero, while in class (2) remains essentially constant with decreasing T [9-11] and n ph [12]. Another, seemingly distinct, puzzle concerns the sign of the photoinduced change in sample reflectivity, R, which can be either positive or negative [2,9,13-15].Here we report measurements of R and in the Bi 2 Sr 2 Ca 1ÿy Dy y Cu 2 O 8 (BSCCO) system of cuprate superconductors as a function of hole concentration, x, that considerably clarify the conditions under which these behaviors appear. As discussed below, the key to successfully exploring the BSCCO system was to eliminate the effects of laser-induced heating. Once this is accomplished, we find that the dynamics change from class (1) to (2) at exactly x m , the value for which the superconducting transition temperature T c is maximal. Moreover, we find that the sign of R reverses at x m as well. These coincident changes suggest that an abrupt transition in quasiparticle dynamics takes place precisely at optimal doping in the BSCCO system.Time-resolved optical spectroscopy was performed using pump and probe pulses of photon energy 1.5 eV and duration 80 fs from a mode-locked Ti:Sapphire oscillator. Because the BSCCO crystals are optically thick at the laser wavelength of 820 nm, the changes in optical response were probed by measuring the reflected probe power. Figure 1 is a plot of the initial reflectivity change, R, normalized to the reflectivity R, as...

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Abrupt Transition in Quasiparticle Dynamics at Optimal Doping in a Cuprate Superconductor System

et al. 2005

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“…In both Q gradually decreases upon increasing T towards T c [4,5,6,7,8,9,10,14], while the low-T relaxation time increases when T −→ 0. The only exception thus far was the near optimally doped YBCO, where τ is roughly constant at low-T [4,6]. The main difference between cuprates and conventional SC is a 1-2 orders of magnitude difference in τ , which can be understood in terms of an order of magnitude difference in the value of the SC energy gap [16].…”

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“…The two datasets capture the main features observed on other conventional [10,14] or cuprate [4,5,6,7,8,9] superconductors. In both Q gradually decreases upon increasing T towards T c [4,5,6,7,8,9,10,14], while the low-T relaxation time increases when T −→ 0. The only exception thus far was the near optimally doped YBCO, where τ is roughly constant at low-T [4,6].…”

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“…Analytical solutions for various limiting cases are obtained. The model is found to account for the intensity and temperature dependence of both photoinduced quasiparticle density, as well as pair-breaking and superconducting state recovery dynamics in conventional as well as cuprate superconductors.In recent years numerous studies of non-equilibrium carrier dynamics in superconductors (SC) have been performed utilizing femtosecond real-time techniques [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Research focused on the identification of relaxation processes and direct measurements of the relaxation times.…”

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Kinetics of a Superconductor Excited with a Femtosecond Optical Pulse

2005

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Superconducting state dynamics following excitation of a superconductor with a femtosecond optical pulse is studied in terms of a phenomenological Rothwarf and Taylor model. Analytical solutions for various limiting cases are obtained. The model is found to account for the intensity and temperature dependence of both photoinduced quasiparticle density, as well as pair-breaking and superconducting state recovery dynamics in conventional as well as cuprate superconductors.In recent years numerous studies of non-equilibrium carrier dynamics in superconductors (SC) have been performed utilizing femtosecond real-time techniques [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Research focused on the identification of relaxation processes and direct measurements of the relaxation times.One of the open issues at the moment is whether cuprates are in the so called phonon bottleneck regime as conventional SCs [19], or in the weak bottleneck regime, where relaxation is governed by the biparticle recombination kinetics [9,17,18]. The theoretical model that has been most commonly used to interpret the dynamics is a phenomenological Rothwarf-Taylor (RT) model which describes the evolution of quasiparticle (QP) and high frequency phonon (HFP) populations via a set of two non-linear differential equations [20], which were shown recently[21] to follow from the general set of kinetic equations for a SC [22]. While the RT model has been known for almost 40 years, no rigorous attempt to solve it has been made thus far, and neither has a comparison to the experimental data been made.In this Letter we present a detailed study of the evolution of the SC state following excitation by ultrashort laser pulse using the RT model. We have obtained analytical solutions of the model in the limit of a strong and a weak bottleneck, which are in excellent agreement with numerical simulations. The solutions enable comparison of the model to the experimental results. We show that RT model can account for most of the experimental observations in conventional as well as cuprate SC, and that both conventional and cuprates SCs are in the strong bottleneck regime, where SC state recovery is governed by the HFP decay dynamics.Rothwarf and Taylor have pointed out that the phonon channel should be considered when studying the SC relaxation [20]. When two QPs with energies ≥ ∆, where ∆ is the SC gap, recombine a HFP (ω > 2∆) is created. Since HFP can subsequently break a Cooper pair creating two QPs the SC recovery is governed by the decay of the HFP population. The dynamics of QP and HFP populations is determined by [20]:Here n and N are concentrations of QPs and HFPs, respectively, η is the probability for pair-breaking by HFP absorption, and R the bare QP recombination rate with the creation of a HFP. N T is the concentration of HFP in thermal equilibrium at temperature T , and γ their decay rate. I 0 and J 0 represent the external sources of QPs and HFPs, respectively [12]. Physically γ is governed by the fastest of the two processes: ...

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“…Previous experiments have used visible or IR ultrafast pump pulses with either visible, IR, or THz probe pulses [1][2][3][4][5] to determine various contributions to the overall recombination mechanism in thin films of doped YBa 2 Cu 3 O 7- (YBCO). In these studies, the pump light breaks superconductivity by exciting electrons with hundreds to thousands of meV of energy, which then relax by transferring energy into phonon modes in the crystal.…”

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Nonlinear ultrafast dynamics of high temperature YBa₂Cu₃O_7–δsuperconductors probed with THz pump / THz probe spectroscopy

Perkins

Hwang

Grady

et al. 2013

EPJ Web of Conferences

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Abstract. High power THz pulses induce near transparency in superconductive YBCO thin films below the critical temperature. THz pump/THz probe measurements reveal a decay of the induced transparency on the time scale of a few picoseconds.High-T c superconductors have been studied with ultrafast pump-probe experiments to understand the mechanism through which superconductivity is destroyed by light and then recovered by recombination of electrons to form Cooper pairs [1][2][3]. Previous experiments have used visible or IR ultrafast pump pulses with either visible, IR, or THz probe pulses [1][2][3][4][5] to determine various contributions to the overall recombination mechanism in thin films of doped YBa 2 Cu 3 O 7- (YBCO). In these studies, the pump light breaks superconductivity by exciting electrons with hundreds to thousands of meV of energy, which then relax by transferring energy into phonon modes in the crystal. To complicate matters, the excited phonons break other Cooper pairs as the system returns to thermal equilibrium [3]. The goal of our experiment is to explore recombination dynamics as strong THz pulses excite electrons in YBCO above the superconductive gap to break superconductivity in ways that limit the excess energy below that needed to populate optic phonons.The thin films were studied with high-power time-domain THz spectroscopy in an apparatus that was configured first for nonlinear transmission measurements and second for THz pump-THz probe scans [6]. High-energy THz pulses were produced by nonlinear rectification of amplified femtosecond pulses ( = 800 nm,  = 100 fs, energy = 6 mJ/pulse) in lithium niobate in a tilted pulse front configuration, yielding field strengths up to 200 kV/cm when focused at the sample. The pump and probe THz pulses were generated co-linearly through optical rectification of two variably delayed 800-nm pulses. The 50-nm YBCO thin film on LaAlO 3 and its matching 500 m reference substrate were mounted in a free-flowing liquid helium cryostat for the measurements. Transmitted time-dependent electric fields were recorded for the thin film sample and the reference for a range of temperatures and THz light intensities. Transmission spectra of a YBCO thin film at 20 K, 80K, and 99K are plotted in Figure 1a for THz field strengths that range from 100 to 200 kV/cm. The transmission spectra are nearly flat across the experimental bandwidth, and the average transmission increases with both field strength and temperature. The most dramatic field-dependent changes occur at lowest temperatures, yet nonlinear effects are also observed above T c .

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Nonequilibrium superconductivity and quasiparticle dynamics inYBa2Cu3O

Cited by 119 publications

References 23 publications

Abrupt Transition in Quasiparticle Dynamics at Optimal Doping in a Cuprate Superconductor System

Abrupt Transition in Quasiparticle Dynamics at Optimal Doping in a Cuprate Superconductor System

Kinetics of a Superconductor Excited with a Femtosecond Optical Pulse

Nonlinear ultrafast dynamics of high temperature YBa₂Cu₃O_7–δsuperconductors probed with THz pump / THz probe spectroscopy

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Nonequilibrium superconductivity and quasiparticle dynamics inYBa2Cu3O

Cited by 119 publications

References 23 publications

Abrupt Transition in Quasiparticle Dynamics at Optimal Doping in a Cuprate Superconductor System

Abrupt Transition in Quasiparticle Dynamics at Optimal Doping in a Cuprate Superconductor System

Kinetics of a Superconductor Excited with a Femtosecond Optical Pulse

Nonlinear ultrafast dynamics of high temperature YBa2Cu3O7–δsuperconductors probed with THz pump / THz probe spectroscopy

Contact Info

Product

Resources

About

Nonlinear ultrafast dynamics of high temperature YBa₂Cu₃O_7–δsuperconductors probed with THz pump / THz probe spectroscopy