Effect of oxygen deficiency (δ) on normal state resistivity of YBa2Cu3O7-δ superconductors (original) (raw)
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Oxygen deficiency dependence of transition temperature in (Sm, Er) Ba2Cu3O7−δ superconductors
Bulletin of Materials Science, 1997
We have investigated the effects of oxygen deficiency (6) on the transition temperature (To) of (Sin, Er)Ba2CU3OT_ ~ superconductors by incorporating the effects of the two dimensional (2I)) acoustic phonons and plasmons in the framework of strong coupling theory. The proposed approach for yttrium cuprates properly takes care of the double CuO 2 plane in a unit cell and has been found earlier to be successful in describing the pairing mechanism as well as the variation of T c with 6 in YBa2CU3OT_ 6 system. The coupling strength (2), the screening parameter (/~*) and the two dimensional acoustic phonon (plasmon) energy hco (oJ +) as a function of oxygen deficiency is worked out. Finally, the transition temperature is evaluated and is found to be consistent with the earlier experimental data on yttrium euprates. Thus, coupled phonon-plasmon mechanism is adequate to understand the nature of pairing mechanism and oxygen deficiency dependence of transition temperature in 90 K (Sm, Er) Ba 2 Cu 3 0 7-6 superconductors.
Electron and phonon characteristics of YBa2Cu3O7−δ
Physica C: Superconductivity, 1995
In this work the experimental results of heat capacity are presented for superconducting yttrium ceramics YBa2Cu30 7_ 8 in the temperature interval 5-300 K. The electron component yT was separated in the normal state (above To). For this purpose, the special technique of data processing had been used which allowed one to extract both the electron component of heat capacity yT and the moments of phonon density of states 0 2, O 4 and some effective moment O, attributed to the phonon spectrum boundary. 0921-4534/95/$09.50
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)
Solid State Communications, 1988
The self-emsr~ of phonons due to nperconductivity is eslculsted in the weak and the strong coup]in s limit. Applyin 8 the theory to Y BqGT,sOT-L we find the ~ results: a) The signs of the observed ~" = 0 ph(mon shifts due to supercoaductivity di~pree in Se~rsl with the predictions of the wesk-coup]ing case; this result sussem that electrtmie traadticm are not ~pomdble for the electron ps/rb~; b) the mq~itude of the obmm~ skd/ts (as well as the value of T,) can comdstently and semi-qunststively he explained by row
Effect of oxygen deficiency (δ) on transition temperature of yttrium cuprate superconductors
Bulletin of Materials Science, 1996
The nature of pairing mechanism as well as transition temperature of yttrium cuprates is discussed using the strong coupling theory. An interaction potential has been developed for the layered structure with two conducting CuO2(a-b) layers in a unit cell. The interaction potential propcrly takes care ofelectron electron, electron phonon and electron-plasmon interactions. Furthermore, the electron phonon coupling parameter (2), the modified Coulomb repulsive parameter (~:*t and the 2D acoustic phonon (plasmon) energy as a function of oxygen deficiency is worked out. Finally, the superconducting transition temperature (T~J is then evaluated by using these coupling parameters and obtained T~ = 9502)K for Y(Yb)Ba2Cu30~ , superconductors with ¢¢, = 0-0. The model parameters estimated from the layered structure approach are consistent with the strong coupling theory. The result deduced on the variation of T~ with 6 are in fair agreement with the earlier reported data on yttrium cuprates. The analysis of the above results are discussed.
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.
In-plane anisotropy and temperature dependence of oxygen phonon modes in YBa2Cu3O6.6
Physica C: Superconductivity, 2003
Inelastic pulsed neutron scattering measurements on YBa 2 Cu 3 O 6.95 single crystals indicate that the sample has a distinct a-b plane anisotropy in the oxygen vibrations. The Cu-O bond-stretching-type phonons, which are suspected to interact strongly with charge, are simultaneously observed along the a and b directions due to a 7-meV splitting arising from the orthorhombicity, even though the sample is twinned. The bond-stretching LO branch with the polarization along a ͑perpendicular to the chain͒ loses intensity beyond the middle of the zone, indicating branch splitting as seen in doped nickelates, with the second branch being located at 10 meV below. The mode along b has a continuous dispersion. These modes show temperature dependence, which parallels that of superconductive order parameter, suggesting significant involvement of phonons in the superconductivity of this compound.
Physica C: Superconductivity, 2010
In this paper, we undertake a quantitative analysis of observed temperature-dependent in-plane normal state electrical resistivity of single crystal YBa 2 Cu 4 O 8. The analysis is within the framework of classical electron-phonon i.e., Bloch-Gruneisen model of resistivity. It is based on the inherent acoustic (low frequency) phonons (x ac) as well as high frequency optical phonons (x op), the contributions to the phonon resistivity were first estimated. The optical phonons of the oxygen breathing mode yields a relatively larger contribution to the resistivity compared to the contribution of acoustic phonons. Estimated contribution to in-plane electrical resistivity by considering both phonons i.e., x ac and x op , along with the zerolimited resistivity, when subtracted from single crystal data infers a quadratic temperature dependence over most of the temperature range [80 6 T 6 300]. Quadratic temperature dependence of q diff. = [q exp À {q 0 + q eÀph (=q ac + q op)}] is understood in terms of electron-electron inelastic scattering. The relevant energy gap expressions within the Nambu-Eliashberg approach are solved imposing experimental constraints on their solution (critical temperature T c). It is found that the indirect-exchange formalism provides a unique set of electronic parameters [electron-phonon (k ph), electron-charge fluctuations (k pl), electron-electron (l) and Coulomb screening parameter (l Ã)] which, in particular, reproduce the reported value of T c .