A review of electron-phonon coupling seen in the high-Tc superconductors by angle-resolved photoemission studies (ARPES) (original) (raw)
Unconventional electron-phonon interactions in high-temperature superconductors
Physical Review B, 1991
The infrared absorption of the 155-cm c-axis mode of YBa2Cu307 is calculated on the basis of an anharmonic-electron-phonon-interaction model and a large enhancement of its intensity is obtained. A double-well potential in the electron-phonon interaction gives the right order of magnitude for shifts in the bridging O(4) position in agreement with recent extended x-ray-absorption fine-structure data. Electron-density-two-phonon-interaction terms are derived which represent a violation of the Migdal theorem and a BCS-type superconducting state with nonlinearly enhanced electron-phonon coupling is expected together with an anisotropy of the superconducting energy gap.
Anisotropic Electron-Phonon Coupling Uncovered By Angle-Resolved Photoemission
Recently there has been an accumulation of experimental evidence in the high temperature superconductors suggesting the relevance of electron-phonon coupling in these materials. These findings challenge some well-held beliefs of what electron-phonon interactions can and cannot do. In this article we review evidence primarily from angleresolved photoemission (ARPES) measurements which point out the importance of electronic coupling to certain phonon modes in the cuprates.
Enhanced electron–phonon coupling and its irrelevence to high Tc superconductivity
Solid State Communications, 1998
It is argued that the origin of the buckling of the CuO2 planes in certain cuprates as well as the strong electron-phonon coupling of the B1g phonon is due to the electric field across the planes induced by atoms with different valence above and below. The magnitude of the electric field is deduced from new Raman results on YBa2Cu3O6+x and Bi2Sr2(Ca1−xYx)Cu2O8 with different O and Y doping, respectively. In the latter case it is shown that the symmetry breaking by replacing Ca partially by Y enhances the coupling by an order of magnitude, while the superconducting Tc drops to about two third of its original value.
By applying a state-of-the-art angle-resolved photoemission to LiFeAs, the only stoichiometric pnictide superconductor without magnetic ordering, we identify a clear fingerprint of the phonon spectrum in the fermionic self-energy and estimate the electron-phonon coupling strength, which appears to be sufficient to mediate the superconductivity. This result suggests that the superconductivity in pnictides could be based on the conventional phonon pairing enhanced by the van Hove singularity in the electronic density of states and by the strong electron-electron interaction.
Electron-Phonon Coupling and Superconductivity in Strongly Polar Semimetals
Japanese Journal of Applied Physics, 1987
The popular idea of Tc max\doteq30–40K for electron-phonon (E-P) mechanism is based on an estimation of E-P coupling strength in usual cation metallic solids. However, we have made a model study of the interaction of itinerant electrons with anion cores, Y–Ba–Cu–O is believed to be the case, in LMTO formulation. It turns out that anion repulsive core favours the high angular momentum hybridization of the itinerant wave-function around it. Thus, we will have a strong E-P coupling of λ\doteq1.3 with optical ω\doteq77mev so a Tc of the order of 90K.
Synergetic Phonon–Spin–Charge Mechanism of High-Temperature Superconductivity
Journal of Superconductivity, 2004
For a long time the majority opinion in the field of high-temperature superconductivity (HTSC) has been that it is purely an electronic phenomenon involving spin, and could be explained by a t-J Hamiltonian. Phonons and local distortion were regarded as irrelevant or harmful to HTSC. However, various experimental results indicate strong phonon involvement and ubiquitous presence of local spin-charge-lattice inhomogeneity. We suggest that the electronphonon (e-p) coupling in the cuprate is unconventional, and a synergetic coupling of spin, charge, and phonon could explain the HTSC phenomenon. In our view the spin-charge-lattice inhomogeneity is a signature of such a coupling and an important component of the HTSC mechanism.
The theory of thermal conductivity of high temperature superconductors (HTS) based on electron and phonon line width (life times) formulation is developed with Quantum dynamical approach of Green's function. The frequency line width is observed as an extremely sensitive quantity in the transport phenomena of HTS as a collection of large number of scattering processes. The role of resonance scattering and electron-phonon interaction processes is found to be most prominent near critical temperature. The theory successfully explains the spectacular behaviour of high T c superconductors in the vicinity of transition temperature. A successful agreement between theory and experiment has been obtained by analyzing the thermal conductivity data for the sample La 1.8 Sr 0.2 Cu O 4 in the temperature range 0 − 200K . The theory is equally and successfully applicable to all other high T c superconductors.
Electron Phonon Interactions and Superconductivity
Electron–Phonon Interactions and Superconductivity in (Cu 0.5 Tl 0.5)Ba 2 Ca 3 (Cu 4−y Ti y)O 12−δ (y = 0, 0.25, 0.50, 0.75, 1.0) Abstract We have used two-step solid state reaction method for the synthesis of (Cu 0.5 Tl 0.5)Ba 2 Ca 3 (Cu 4−y Ti y) O 12−δ (y = 0, 0.25, 0.50, 0.75, 1.0) superconductors at 880 • C. The oxygen contents in the samples were optimized by carrying out self-doping which is accomplished by post-annealed in flowing oxygen environment at 500 • C for approximately 5 h. The superconducting properties of all the samples were improved, after the self-doping of the carriers in the conducting planes. In the x-ray diffraction scans of the samples, the a-axis length of tetragonal unit cell increases whereas the c-axis decreases with increased Ti doping in the final compound. The Fourier transform infrared spectrometer (FTIR) absorption measurements of these samples have shown that the apical oxygen mode at 548 cm −1 and the pla-nar oxygen mode at 596 cm −1 are softened with increased Ti doping. The origin of softening of planar oxygen mode lies in increase bond lengths of apical oxygen atoms promoted by larger covalent radius of Ti (1.32Å) atoms relative to Cu (1.17Å) atoms that in turn promotes the softening of the apical oxygen modes. Doped Ti (47.90 amu) atoms at the Cu (63.54 amu) sites initiate the an-harmonic oscillations resulting into the suppression of density of phonon modes. The suppression in the values of superconductiv-ity parameters with Ti doping at the Cu sites shows the essential role of phonon in mechanism of high T c supercon-ductivity and hence the electron–phonons interactions. The excess conductivity analyses (FIC) of conductivity data of oxygen-post-annealed samples have shown decrease in the mean field critical temperature, coherence length along the c-axis, interlayer coupling, and Fermi velocity with increase Ti doping. However, the values of B c , B c1 , and J c(0) increase with Ti doping, showing increase in the population of the pinning centers.