arXiv subjects

S. N. Kamchatnaya

Publications and source records attributed to S. N. Kamchatnaya.

5 recordsLinked to original sources

arXiv2025

Evolution of the pseudogap and excess conductivity of YBa$_2$Cu$_3$O$_{7-δ}$ single crystals in the course of long-term aging

The temperature dependences of both fluctuation conductivity (FLC) $σ^\prime(T)$ and pseudogap (PG) $Δ^*(T)$ derived from measurements of resistivity $ρ(T)$ of an optimally doped YBa$_2$Cu$_3$O$_{7-δ}$ single crystal subjected to long-term storage have been studied. The as-grown sample S1 exhibits characteristics typical of optimally doped YBa$_2$Cu$_3$O$_{7-δ}$ single crystals containing twins and twin boundaries. Analysis of both FLC and PG showed an unexpected improvement in all characteristics of the sample after 6 years of storage (sample S2), indicating that the effect of twin boundaries is somehow limited. After 17 years of storage, all characteristics of the sample changed dramatically, which indicates a strong influence of internal defects formed during the aging process. For the first time, the temperature dependences of both FLC and PG were obtained after 17 years of storage.

cond-mat.supr-con↗

arXiv2019

Influence of annealing on the electrical resistance of YBCO single crystals

The effect of annealing on the basal-plane electrical resistivity of the YBa$_2$Cu$_3$O$_{7-δ}$ single crystals is studied in a broad range of oxygen contents. Within the framework of s-d scattering of electrons by phonons, an increase in the oxygen deficit index, $δ$, leads to a significant increase in the Debye temperature, $θ$, which is associated with the isotropization of the phonon spectrum as the concentration of oxygen vacancies increases. Near the optimal doping, the role of the paraconductivity becomes crucial, whereas its contribution decreases with increasing $δ$. At large values of $δ$ some deviations from the s-d model of electron scattering by phonons are observed at room temperature, while no paraproductivity is observed. In the superconducting transition region, a 2D-3D crossover is observed, which shifts in the direction of $T_c$ with increasing $δ$. The estimate for the transverse coherence length is about $1$\,Å.

cond-mat.supr-con↗

arXiv2019

Annealing effects on the normal-state resistive properties of underdoped cuprates

The influence of room-temperature annealing on the parameters of the basal-plane electrical resistance of underdoped YBa$_2$Cu$_3$O$_{7-δ}$ and HoBa$_2$Cu$_3$O$_{7-δ}$ single crystals in the normal and superconducting states is investigated. The form of the derivatives $dρ(T)/dT$ makes it possible to determine the onset temperature of the fluctuation conductivity and indicates a nonuniform distribution of the labile oxygen. Annealing has been revealed to lead to a monotonic decrease in the oxygen deficiency, that primarily manifests itself as a decrease of the residual resistance, an increase of $T_c$, and a decrease of the Debye temperature.

cond-mat.supr-con↗

arXiv2019

Room-temperature annealing effects on the basal-plane resistivity of optimally doped YBa$_2$Cu$_3$O$_{7-δ}$ single crystals

We reveal that the temperature dependence of the basal-plane normal-state electrical resistance of optimally doped YBa$_2$Cu$_3$O$_{7-δ}$ single crystals can be with great accuracy approximated within the framework of the model of s-d electron-phonon scattering. This requires taking into account the fluctuation conductivity whose contribution exponentially increases with decreasing temperature and decreases with an increase of oxygen deficiency. Room-temperature annealing improves the sample and, thus, increases the superconducting transition temperature. The temperature of the 2D-3D crossover decreases during annealing.

cond-mat.supr-con↗

arXiv2018

Peculiarities in the pseudogap behavior in optimally doped YBa2Cu3O7-δ single crystals under pressure up to 1GPa

The influence of the hydrostatic pressure P up to 0.95 GPa on the excess conductivity and the pseudogap Δ*(T) in optimally doped YBCO single crystals (T_c = 91.1K at ambient pressure) is investigated by electrical resistivity measurements. A pronounced enhancement of the pseudogap under pressure of dlnΔ*/dP= 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 2Δ*(T_c)/k_BT_c=5 at P=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 T_c is minor: dT_c/dP=+0.73 K/GPa, whereas dlnρ/dP=-17% 1/GPa is comparable with that in lightly doped YBCO single crystals. This suggests that the mechanisms of the pressure effect on ρ(T) and T_c are noticeably different. Independently of pressure, near T_c, the excess conductivity is well described by the Aslamazov-Larkin (3D-AL) and 2D Hikami-Larkin fluctuation theories, exhibiting a 3D-2D crossover with increasing temperature. However, the temperature interval T_c<T<T_{01}, in which excess conductivity obeys the classical fluctuation theories, is exceptionally narrow (~1.16 K). Nevertheless, a peculiarity at the temperature T_{01}, up to which the wave function phase stiffness in the superconductor is maintained, is clearly observed in the dependence Δ*(T). Below T_{01} a fast growth of Δ*(T) is revealed for the first time. It can be associated with a sudden increase of the superfluid density, n_s, that is the density of fluctuating Cooper pairs (short-range phase correlations) forming in the sample when T approaches T_c.

cond-mat.supr-con↗