Transition temperature and energy gap for superconductors with strong coupling

Geilikman, B.T.; Kresin, Vladimir Z.; Masharov, N.F.

doi:10.1007/bf00118156

Cited by 65 publications

(21 citation statements)

References 9 publications

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“…The saturation value proves to be 5.2 for μ = 0.3. We stress that such large enhancement of 2Δ(0)/T c agrees well with experimental data [441,478,631,632] for cuprates and cannot be achieved taking into account strongcoupling electron-boson interaction effects for reasonable relationships between T c and effective boson frequencies ω E [633,634] (one can hardly accept, e.g., the value T c /ω E ≈ 0.3 [634] as practically meaningful). Furthermore, the destruction of the alternating-sign superconducting order parameter by impurity scattering approximated by collective boson modes also could not explain [635] high values of 2Δ(0)/T c , for example, inherent to underdoped BSCCO [347,597].…”

Section: Coexistence Of Cdws and D-wave Superconductivitysupporting

confidence: 59%

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

Gabovich

Войтенко

Ekino

et al. 2010

Advances in Condensed Matter Physics

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Explicit and implicit experimental evidence for charge density wave (CDW) presence in high-Tcsuperconducting oxides is analyzed. The theory of CDW superconductors is presented. It is shown that the observed pseudogaps and dip-hump structures in tunnel and photoemission spectra are manifestations of the same CDW gapping of the quasiparticle density of states. Huge pseudogaps are transformed into modest dip-hump structures at low temperatures,T, when the electron spectrum superconducting gapping dominates. Heat capacity jumps at the superconducting critical temperature and the paramagnetic limit are calculated for CDW superconductors. For a certain range of parameters, the CDW state in ad-wave superconductor becomes reentrant withT, the main control quantity being a portion of dielectrcally gapped Fermi surface. It is shown that in the weak-coupling approximation, the ratio between the superconducting gap at zero temperatureΔ(T=0)andTchas the Bardeen-Cooper-Schrieffer value fors-wave Cooper pairing and exceeds the corresponding value ford-wave pairing of CDW superconductors. Thus, large experimentally found values2Δ(T=0)/Tc≈5÷8are easily reproduced with reasonable input parameter values of the model. The conclusion is made that CDWs play a significant role in cuprate superconductivity.

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Section: Coexistence Of Cdws and D-wave Superconductivitysupporting

confidence: 59%

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

Gabovich

Войтенко

Ekino

et al. 2010

Advances in Condensed Matter Physics

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“…The saturation value proves to be 5.2 for µ = 0.3. Such a large enhancement of ∆(0)/T c consistent with experiment cannot be achieved taking into account strong-coupling electron-boson interaction effects for reasonable relationships between T c and effective boson frequencies ω E [270,271] (one can hardly accept, e.g., the value T c /ω E ≈ 0.3 [271] as practically meaningful). Therefore, our weak-coupling model is sufficient to explain large ∆(0)/T c in cuprates, possible strong-coupling effects resulting in at most minor corrections.…”

Section: Unidirectional Cdw Configurationmentioning

confidence: 90%

d-Wave Superconductivity and s-Wave Charge Density Waves: Coexistence between Order Parameters of Different Origin and Symmetry

Ekino

Gabovich

et al. 2011

Symmetry

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A review of the theory describing the coexistence between d-wave superconductivity and s-wave charge-density-waves (CDWs) is presented. The CDW gapping is identified with pseudogapping observed in high-T c oxides. According to the cuprate specificity, the analysis is carried out for the two-dimensional geometry of the Fermi surface (FS). Phase diagrams on the σ 0 − α plane-here, σ 0 is the ratio between the energy gaps in the parent pure CDW and superconducting states, and the quantity 2α is connected with the degree of dielectric (CDW) FS gapping-were obtained for various possible configurations of the order parameters in the momentum space. Relevant tunnel and photoemission experimental data for high-T c oxides are compared with theoretical predictions. A brief review of the results obtained earlier for the coexistence between s-wave superconductivity and CDWs is also given.

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“…One can use the close expression, obtained analytically by Geilikman et al(1975), valid also for λ opt ! < 1.5:…”

Section: B Critical Temperatures For Different Phasesmentioning

confidence: 99%

Colloquium : High pressure and road to room temperature superconductivity

Gor’kov¹,

Kresin²

2018

Rev. Mod. Phys.

134

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High pressure serves as a path finding tool towards novel structures, including those with very high Tc. The superconductivity in sulfur hydrides with record value of Tc =203 K (!) is caused by the phonon mechanism. However, the picture differs from the conventional one in important ways. The phonon spectrum in sulfur hydride is both broad and has a complex structure. High value of T c is mainly due to strong coupling to the high-frequency optical modes, although the acoustic phonons also make a noticeable contribution. New approach is described; it generalizes the standard treatment of the phonon mechanism and makes it possible to obtain an analytical expression for Tc . It turns out that, unlike in the conventional case, the value of the isotope coefficient varies with the pressure and reflects the impact of the optical modes. The phase diagram, that is the pressure dependence of Tc, is rather peculiar. A crucial feature is that increasing pressure results in a series of structural transitions, including the one, which yields the superconducting phase with the record Tc . In a narrow region near P≈150 GPa the critical temperature rises sharply from Tc ≈120K to Tc ≈200K. The sharp structural transition, which produces the high Tc phase, is a first-order phase transition caused by interaction between the order parameter and lattice deformations. A remarkable feature of the electronic spectrum in the high Tc phase is the appearance of small pockets at the Fermi level. Their presence leads to a two-gap spectrum, which 2 can, in principle, be observed, with the future use of tunneling spectroscopy. This feature leads to non-monotonic and strongly asymmetric pressure dependence of Tc. Other hydrides can be expected to display even higher values of Tc, up to room temperature. The fundamental challenge lays in creation a structure capable of displaying high Tc at ambient pressure.

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Transition temperature and energy gap for superconductors with strong coupling

Abstract: The ratio of the energy gap e(O) for T = 0 to the transition temperatur~e T c, the value of energy gap e(T) near T c, and the expression for the transition temperature are calculated within the framework of the strong coupling theory.

Cited by 65 publications

References 9 publications

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

Competition of Superconductivity and Charge Density Waves in Cuprates: Recent Evidence and Interpretation

d-Wave Superconductivity and s-Wave Charge Density Waves: Coexistence between Order Parameters of Different Origin and Symmetry

Colloquium : High pressure and road to room temperature superconductivity

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