Relaxation timescales and electron-phonon coupling in optically pumped YBa2Cu3O6+x revealed by time-resolved Raman scattering (original) (raw)
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Physical Review B
The interaction between phonons and high-energy excitations of electronic origin in cuprates and their role in the superconducting mechanisms is still controversial. Here we use coherent vibrational time-domain spectroscopy together with density functional and dynamical mean-field theory calculations to establish a direct link between the c-axis phonon modes and the in-plane electronic charge excitations in optimally doped YBCO. The non-equilibrium Raman tensor is measured by means of the broadband "coherent-phonon" response in pump-probe experiments and is qualitatively described by our model using DFT in frozen phonon approximation plus single band DMFT to account for the electronic correlations. The major outcome of our experimental and theoretical study is to establish the link between out-of-plane copper ions displacements and the inplane electronic correlations, and to estimate at few unit cells the correlation length of the associated phonon mode. The approach introduced here could help revealing the complex interplay between fluctuations of different nature and spatial correlation in several strongly-correlated materials.
Physical Review Letters, 2010
We measure the anisotropic mid-infrared response of electrons and phonons in bulk YBa 2Cu3O7−δ after femtosecond photoexcitation. A line shape analysis of specific lattice modes reveals their transient occupation and coupling to the superconducting condensate. The apex oxygen vibration is strongly excited within 150 fs demonstrating that the lattice absorbs a major portion of the pump energy before the quasiparticles are thermalized. Our results attest to substantial electron-phonon scattering and introduce a powerful concept probing electron-lattice interactions in a variety of complex materials. 74.25.Kc, 78.47.jg The interaction of electrons with the crystal lattice represents one of the most elusive, yet pivotal aspects of high-temperature superconductors (HTSCs). Although purely phonon-mediated BCS-type pairing fails to explain essential properties of superconducting (SC) cuprates, convincing evidence of significant electronphonon contributions have been provided by angleresolved photoemission [1-3], inelastic neutron scattering [4], tunneling [5] and Raman [6] spectroscopies. For time-integrated techniques it is difficult, however, to disentangle the interplay between elementary excitations.
CuO-chain Raman scattering and photoinduced metastability inYBa2Cu3Ox
Physical Review B, 1998
Raman measurements in YBa 2 Cu 3 O x (xϭ6.72-6.82͒ high-T c superconductors reveal intense phonon scattering due to an electronic resonance localized near oxygen vacancies on the CuO chains. Below room temperature the resonance can be photobleached in a manner similar to reported persistent photoinduced superconductivity effects, indicating photon-assisted oxygen ordering or electron vacancy capture. By comparing Raman and x-ray diffraction data we establish a correlation between the stability of the photoinduced state and the oxygen-ordering kinetics in the CuO chains. ͓S0163-1829͑98͒50222-6͔ RAPID COMMUNICATIONS
Intensity anomalies of Raman-active phonons in the superconducting state of YBa2Cu3O7-[delta]
Solid state …, 1991
We report anomalous intensity increases, by up to a factor of 2, of Raman-active phonons in YBa~CuaOT_s below the superconducting transition temperature. This effect can be explained as a superconductivity-induced resonant Raman process stemming from the resonance of the phonons with the superconducting gap. In the normal state a continuous increase of the Raman efficiency was observed for most phonons upon cooling from 300 K to To. All relative changes in 'intensity seem to be rather independent of the exciting laser energy used (1.92, 2.34, and 2.60 eV).
Superconductivity induced phonon anomalies in the Raman spectra of Zn and Ni doped YBa2Cu3O7
European Physical Journal B, 1994
Here we present Raman spectra of YBa2(Cul_xZnx)30 7 and YBa2(Cul_~Nix)307 as a function of temperature and Zn or Ni content. The temperature dependence of two modes at 340 and 440 cm-1 is analyzed. Similarly to the infrared measurements it is found that Zn substantially suppresses the superconductivity induced phonon softening whereas, Ni does not affect much that effect. Moreover, the superconductivity induced phonon stiffening of the 440 cm 1 mode completely disappeared with the Zn doping. We find this behaviour might support the model where Zn acts effectively as a magnetic pair breaker.
Physical Review B
We discuss the mechanism of coherent phonon generation by Stimulated Ionic Raman Scattering, a process different from conventional excitation with near visible optical pulses. Ionic Raman scattering is driven by anharmonic coupling between a directly excited infrared-active phonon mode and other Raman modes. We experimentally study the response of YBa2Cu3O6+x to the resonant excitation of apical oxygen motions at 20 THz by mid-infrared pulses, which has been shown in the past to enhance the interlayer superconducting coupling. We find coherent oscillations of four totally symmetric (Ag) Raman modes and make a critical assessment of the role of these oscillatory motions in the enhancement of superconductivity.
Femtosecond pump–probe study of YBa2Cu4O8 superconductor
Physica C: Superconductivity, 2000
We report the observation of low-frequency phonons excited by femtosecond laser pulses in the single crystal of YBa Cu O . In the transient time-resolved reflectivity we detect the oscillations associated with two fully symmetric, 2 4 8 metal-ion phonons. We compare the time-and frequency-domain results for YBa Cu O , as well as the coherent phonons in 2 4 8 YBa Cu O and YBa Cu O single crystals. q 2000 Elsevier Science B.V. All rights reserved. 2 4 8 2 3 7
Probing the lattice anharmonicity of superconducting YBa2Cu3O7−δ via phonon harmonics
Physical Review B, 2019
We examine coherent phonons in a strongly driven sample of optimally-doped high temperature superconductor YBa2Cu3O 7−δ. We observe a non-linear lattice response of the 4.5 THz copperoxygen vibrational mode at high excitation densities, evidenced by the observation of the phonon third harmonic and indicating the mode is strongly anharmonic. In addition, we observe how highamplitude phonon vibrations modify the position of the electronic charge transfer resonance. Both of these results have important implications for possible phonon-driven non-equilibrium superconductivity.
Localised vibrations in superconducting YBCO revealed by ultra-fast optical coherent spectroscopy
2017
The interaction between phonons and high-energy excitations of electronic origin in cuprates and their role in the superconducting mechanisms is still controversial. Here we use coherent vibrational time-domain spectroscopy together with density functional and dynamical mean-field theory calculations to establish a direct link between the c-axis phonon modes and the in-plane electronic charge excitations in optimally doped YBCO. The non-equilibrium Raman tensor is measured by means of the broadband 'coherent-phonon' response in pump-probe experiments and is qualitatively described by our model using DFT in frozen phonon approximation plus single band DMFT to account for the electronic correlations. The major outcome of our experimental and theoretical study is to establish the link between out-of-plane copper ions displacements and the in-plane electronic correlations, and to estimate at few unit cells the correlation length of the associated phonon mode. The approach introd...