Localized vibrations in superconducting YBa2Cu3O7 revealed by ultrafast optical coherent spectroscopy (original) (raw)
Related papers
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...
arXiv (Cornell University), 2014
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.
The interaction between phonons and high-energy excitations of electronic origin in cuprates and their role on the superconducting phenomenon 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. Our findings clarify the nature of the anomalous high-energy response associated to the formation of the superconducting phase in the cuprates.
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.
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.
Physical review, 2000
We have investigated the temperature dependence of the optical reflectivity at femtosecond scale in YBa 2 Cu 3 O 7Ϫx superconductors. In both normal and superconducting states, we detect the oscillations associated with two A 1g metal-ion modes and compare the phonon dynamics to those obtained by frequency-domain ͑Raman͒ spectroscopy. Apart from the considerable increase of amplitude for low-frequency mode in the superconducting state, we observe that its initial phase in the time domain is approximately /4 shifted by the superconductivity, whereas for the high-frequency mode the initial phase shift is almost two times larger. Even though similar lattice anomalies are observed in both time and frequency domains, the systematic analysis shows that the coherent lattice dynamics is different from the ordinary ͑thermal state͒ dynamics probed by frequency-domain spectroscopy.
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).
Physical Review B, 2021
Time resolved measurements provide a new way to disentangle complex interactions in quantum materials due to their different timescales. We used pump-probe Raman scattering to investigate the apical oxygen vibration in YBa2Cu3O6.9 under nonequilibrium conditions. Time-dependence of the phonon population demonstrated strong electron-phonon coupling. Most importantly, the phonon shifts to a higher energy due to transient smearing of the Fermi surface in a remarkable agreement with theory. We also discuss new insights into photoinduced superconductivity reported at lower doping that follow from these results.
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.
Physica C: Superconductivity, 1990
The infrared-active phonon spectra of YBa2 ( CoxCu ~ _ x ) 307 _ ~ ( 0 < x < 0.07 ) have been studied between 35 K and room temperature. The mode near 580 cm-~ depends sensitively on Co doping and renormalizes due to the metal-superconductor phase transition. The excess phonon frequency and absorption cross-section scale as the square of the order parameter in the superconducting phase. This temperature evolution is in accordance with Landau-Ginzburg theory including saturation effects, which is numerically similar to BCS behaviour. Phonon contributions to the specific heat as a function of Co content correlate closely with observed anomalies in calorimetric measurements, indicating that phonons contribute intrinsically to the transition mechanism, e.g. via Bose condensation of structural bipolarons. The growth of a phonon doublet at ~ 657 cm-~ is attributed to effects of Co doping and discussed in view of the orthorhombic to tetragonal structural phase transitions at x~0.025 and J~0.5 in the YBa2Cu307_,~ end-member, ~ Notation as used in refs. [4,10]. 0921-4534/90/$03.50 © 1990 -Elsevier Science Publishers B.V. (North-Holland)