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Effect of high pressure on the fluctuation paraconductivity in Y0.95Pr0.05Ba2Cu3O7-d single crystals
R.V. Vovk,N.R. Vovk,G.Ya Khadzhai,O.V. Dobrovolskiy,Z.F. Nazyrov 한국물리학회 2014 Current Applied Physics Vol.14 No.12
The effect of high hydrostatic pressure up to 17 kbar on the fluctuation conductivity of lightly Pr-doped Y1xPrxBa2Cu3O7d (x z 0.05) single crystals is investigated. We show that in contrast to non-doped YBa2Cu3O7d samples, application of a high pressure leads to a substantial increase of the pressure derivative of the coherence length dxc/dP and a temperature shift of the 2D-3D crossover point. Possible mechanisms of the influence of high pressure on the critical temperature and the coherence length are discussed within the framework of a model assuming the presence of singularities in the charge carriers electron spectrum typical for lattices with strong coupling.
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Transverse resistance of YBa2Cu3O7-δ single crystals
R.V. Vovk,G.Ya Khadzhai,O.V. Dobrovolskiy,Z.F. Nazyrov,A. Chroneos 한국물리학회 2015 Current Applied Physics Vol.15 No.5
Measured is the transverse electrical resistance of YBa2Cu3O7-δ single crystals with different oxygen deficiency values (δ) in the temperature range Tc - 300 K. The experimental data are approximated by an empiric expression accounting for the fluctuation conductivity near Tc and the semiconductor-like resistance regime. Our analysis of the concentration dependences of the fitting parameters, in particular, reveals that the resistance temperature dependence is largely affected by the sample's nonhomogeneity. The latter, in turn, causes a Tc anisotropy and variable-range hopping conductivity between different phases. The deduced maximal values of the basal-plane coherence length, ξxy(0), are comparable with those for low-temperature superconductors.
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A.L. Solovjov,L.V. Omelchenko,R.V. Vovk,O.V. Dobrovolskiy,S.N. Kamchatnaya,D.M. Sergeev 한국물리학회 2016 Current Applied Physics Vol.16 No.9
The influence of the hydrostatic pressure P up to 0.95 GPa on the excess conductivity s0(T) and the pseudogap D*(T) in optimally doped YBa2Cu3O7d single crystals (Tc x 91.1 K at ambient pressure) is investigated by electrical resistivity measurements. A pronounced enhancement of the pseudogap under pressure of dlnD*/dP z 0.32, which is only a factor of 1.12 smaller than in slightly doped single crystals, is revealed for the first time. This implies a somewhat more moderate increase of the coupling strength in optimally doped cuprates with increasing pressure. Simultaneously, the ratio 2D*(Tc)/kBTc z 5 at P ¼ 0 GPa, which is typical for high-temperature superconductors with strong coupling, increases by 16% with increasing pressure. At the same time, the pressure effect on Tc is minor: dTc/dP z þ0.73 K GPa1, whereas dlnr/dP z (17 ± 0.2)% GPa1 is comparable with that in lightly doped YBCO single crystals. This suggests that the mechanisms of the pressure effect on r(T) and Tc are noticeably different. Independently of pressure, near Tc, s0(T) is well described by the Aslamazov-Larkin (3D-AL) and 2D Hikami- Larkin fluctuation theories, exhibiting a 3De2D crossover with increasing temperature. However, the temperature interval Tc < T < T01, in which s0(T) obeys the classical fluctuation theories, is exceptionally narrow (z1.16 K). Nevertheless, a peculiarity at the temperature T01, up to which the wave function phase stiffness in the superconductor is maintained, is clearly observed in the dependence D*(T). Below T01 a fast growth of D*(T) is revealed for the first time. It can be associated with a sudden increase of the superfluid density, ns, that is the density of fluctuating Cooper pairs (short-range phase correlations) forming in the sample when T approaches Tc.
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High-pressure effects on basal-plane conductivity of YPrBCO single crystals
Khadzhai G.Ya.,Kamchatnaya S.N.,Korobkov M.V.,Necheporenko Ya.V.,Vovk R.V.,Dobrovolskiy O.V. 한국물리학회 2022 Current Applied Physics Vol.39 No.-
Influence of high hydrostatic pressure up to 12 kbar on the basal-plane electrical resistance of Y1-xPrxBa2Cu3O7-δ single crystals is investigated for moderate Pr doping levels (x ≈ 0.23). The application of high pressure leads to a threefold increase of the derivative dTc/dP in comparison with optimally-doped YBCO single crystals. Possible mechanisms of Tc suppression are discussed with account for features in the electronic spectrum of charge carriers, typical for lattices with strong coupling. The excess conductivity Δσ(T) obeys an exponential temperature dependence in the broad temperature range Tf < T < T*. The dependence Δσ(T) ∼ (1 - T /T∗)exp(Δ∗ab /T) is interpreted in terms of the mean-field theory, where T* is the mean-field temperature of transition to the pseudogap state and the temperature dependence of the pseudogap is described satisfactory within the BCS-BEC crossover theory. All in all, an increase of the pressure results in a narrowing of the pseudogap temperature interval, expanding the temperature range of resistance linear dependence.
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