Abstract
The conducting properties in the basalabplane of pure and Al-dopedYBa2Cu3O7-δsingle crystals before and after long-time exposure in air atmosphere are investigated. It is shown that prolonged aging leads to an increase of the density of effective scattering centers for the normal carriers. The aluminum doping has been revealed to partially slowdown the degradation of the conducting properties in process of aging. The excess conductivity,Δσ(T), has been found to obey exponential dependence in the broad temperature rangeTc<T<T*. In the pseudogap regime, the mean-field transition temperatureT*and the 3D-2D crossover point in the excess conductivity have been quantified. Near the critical temperature,Δσ(T)is described well within the Aslamazov-Larkin theoretical model. Herewith, both aluminum doping and prolonged aging have been found to essentially expand the temperature interval of implementation of the pseudogap state, thus narrowing the linear section in the dependenceρab(T).
Highlights
Despite the fact that almost three decades have passed since the discovery of high-temperature superconductivity (HTSC) [1], the microscopic nature of this phenomenon remains definitively unexplained so far
In accordance with the contemporary views, it is assumed that the key for understanding the nature of HTSC can be in scrutinizing the physical phenomena observed in these compounds in the normal state at temperatures at and above the critical temperature Tc
Whereas thousands of papers are devoted to the treatment of physics of the pseudogap state and the fluctuation conductivity in HTSC compounds, both the nature of the pseudogap state to appear and its role in the formation of the superconducting state still remain unclear
Summary
Despite the fact that almost three decades have passed since the discovery of high-temperature superconductivity (HTSC) [1], the microscopic nature of this phenomenon remains definitively unexplained so far. In the recent years there is a tendency to expand the field of studies regarding the technological use of high-temperature superconductors (HTSCs) [7] This is mostly associated with a more intensive use of these compounds in contemporary microelectronics, telecommunication systems, and so forth. The presence of labile oxygen in YBa2Cu3O7−δ often leads to a nonequilibrium state in the system, which can be induced by temperature [8, 9] or by high pressure [10,11,12] These effects are observed in nonstoichiometric samples in respect of the oxygen content and are absent in samples with low oxygen
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