Abstract
In the study, we have calculated the dependence of the average value of the energy gap amplitude (G) on the hole concentration (p) and temperature (T) for the Bi2Sr2−x La x CuO6+δ (BSLCO) superconductor. The ratio of the zero temperature energy gap to the critical temperature (R G ≡ G(0)/k B T C) and the ratio of the energy gap to the pseudogap temperature ( $R^{\star }_{\mathrm {G}}\equiv G\left (0\right )/k_{\mathrm {B}}T^{\star }$ ) have been estimated on this basis. It has been found that the value of the parameter R G changes for p ∈ in the range from 32.98 to 7.98. On the other hand, $R^{\star }_{\mathrm {G}}$ takes the values from 2.60 to 3.28. The obtained results indicate that in the studied superconductor, the correlation exists only between the value of the energy gap and the pseudogap temperature, which stands in the sharp contrast with the predictions of the classical Bardeen-Cooper-Schrieffer (BCS) theory. In addition, the dependence of the energy gap on the momentum for the hole concentration corresponding to the maximum value of the pseudogap temperature and the maximum value of the critical temperature has been determined. It has been found that the theoretical results reproduce well the experimental data obtained by using the angle-resolved photoemission spectroscopy (ARPES) method.
Highlights
The thermodynamic properties of the high-temperature superconducting state in cuprates can be described quantitatively on the basis of the three postulates [1].The first postulate states: In the superconductivity domain of cuprates, the fundamental role is played by the electrons on the CuO2 planes.From the mathematical point of view, the above assumption means that the electron-hopping integral in the direction perpendicular to the copper-oxygen plane can be ignored in the considerations.It should be noted that the quasi-two-dimensionality of the electron system in cuprates significantly affects only some thermodynamic parameters of the superconducting state
On the other hand, taking into account only the geometrical reduction of the electron system cannot explain the high values of the ratio of the zero-temperature energy gap amplitude (G (0)) to the critical temperature (RG ≡ G (0) /kBTC), which are commonly observed in cuprates [7,8,9,10,11]
The values of the function Gk have been calculated in the presented work for the lowest hole concentration (p = 0.127), where the maximum is reached by the pseudogap temperature and for p = 0.162, where the highest value is taken by the critical temperature
Summary
The thermodynamic properties of the high-temperature superconducting state in cuprates can be described quantitatively on the basis of the three postulates [1]. The second postulate has the following content: In cuprates exists the conventional electron-phonon interaction, which does not have to be strong. This finding indicates that the pairing mechanism in cuprates is not the result of the purely electronic correlation of the Hubbard-type. J Supercond Nov Magn (2015) 28:19–24 electron-phonon interaction alone is not able to wholly explain all the anomalous properties of the high-temperature superconducting state. The last postulate states: In cuprates exist strong electronic correlations, but the electron-electron scattering in the superconductivity domain is inseparably connected with the absorption or emission of vibrational quanta. The obtained results have been compared to the existing experimental data
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