arXiv subjects

L. V. Bludova

Publications and source records attributed to L. V. Bludova.

5 recordsLinked to original sources

arXiv2026

Hydrostatic pressure effect on the pseudogap in Y0.77Pr0.23Ba2Cu3O7-δsingle crystals

We studied the changes of resistivity $ρ(T)$, superconducting transition temperature $T_c$, fluctuation conductivity $σ'(T)$, and pseudogap $Δ^*(T)$ of $Y_{1-x}Pr_xBa_2Cu_3O_{7-δ}$ (YPrBCO) ($x = 0.23$) single crystal under hydrostatic pressure (HP) up to $\sim 1.1$ GPa. Defects created by magnetic inclusions of $PrBa_2Cu_3O_{7-δ}$ (PrBCO) were found to play a significant role in the behavior of the sample. The largest decrease in $ρ(T)$ was found depending on HP at a rate of $d\lnρ(100~K)/dP = -(29 \pm 0.2) \% \cdot GPa^{-1}$. This indicates that the mechanisms of the influence of HP on the $ρ(T)$ and $T_c$ of YPrBCO and $YBa_2Cu_3O_{7-δ}$ single crystals are different. From the analysis of the pseudogap, it was revealed that the mechanism of the interaction of charge carriers with magnetic PrBCO impurities changes three times with increasing HP. Relatively low HP, up to $\sim 0.5$ GPa, promotes the formation of defects caused by PrBCO magnetic inclusions. Starting from 0.6 GPa, the HP neutralizes the influence of magnetic impurities, and the magnetic maximum on $Δ^*(T)$ disappears. Above $\sim 1.0$ GPa, HP aligns the magnetic moments of PrBCO, and the magnetic maximum reappears on $Δ^*(T)$, more pronounced than at $P = 0$.

cond-mat.supr-con↗

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↗

arXiv2025

Influence of strong electron irradiation on fluctuation conductivity and pseudogap in YBa$_2$Cu$_3$O$_7$--$δ$ single crystals

The effect of high-energy electron irradiation on the temperature dependences of the resistivity $ρ(T)$, fluctuation conductivity (FLC), and pseudogap (PG) $Δ^{*}(T)$ of YBa$_2$Cu$_3$O$_7$--$δ$ (YBCO) single crystals without twins was studied. Irradiation causes a linear increase in $ρ(T)$ and a decrease in the superconducting transition temperature $T_c$ with dose $ϕ$. For small $ϕ$, the reduction of $T_c$ follows the Abrikosov--Gorkov (AG) pair-breaking theory, while for large $ϕ$ it is described by the Emery--Kivelson (EK) model, where quantum phase fluctuations dominate. At $ϕ_3 = 2.5 \times 10^{19}$ e/cm$^2$, which corresponds to the AG--EK crossover, the spacing between CuO$_2$ planes $d_{01}$, the coherence length $ξ_c(0)$, and the fluctuation region $T_{\mathrm{fl}}$ increase sharply, and the two-dimensional Maki--Thompson (2D--MT) contribution is replaced by the Aslamazov--Larkin (2D--AL) term. Surprisingly, no signatures of the crossover appear in $ρ(ϕ)$ or $T_c(ϕ)$. At the same $ϕ_3$, a sharp rise in the pseudogap opening temperature $T^{*}$ and in $Δ^{*}$ indicates a possible reduction of the density of states. With further increase in $ϕ$, both PG parameters and their energy scale decrease markedly, and $Δ^{*}(T)$ acquires an unusual form. However, at $ϕ_5 = 5.6 \times 10^{19}$ e/cm$^2$, the temperature dependences of FLC and PG again show behavior typical of well-structured YBCO, regardless of defect density.

cond-mat.supr-con↗

arXiv2025

Effect of a magnetic field up to 9 T on the temperature dependence of the pseudogap in YBa$_2$Cu$_3$O$_{7-δ}$ films

The work analyzes the effect of a magnetic field $B$ directed along the $c$ axis ($B \parallel c$) up to 9~T on the resistivity $ρ(T)$, fluctuation conductivity (FLC) $σ'(T)$ and pseudogap $Δ^*(T)$ in thin films of YBa$_2$Cu$_3$O$_{7-δ}$ with a critical temperature of the superconducting transition $T_c = 88.8$~K. In contrast to previous work, where the magnetic field was directed along the $ab$ plane ($B \parallel ab$), the influence of the field on the sample is stronger due to the contribution of both spin--orbit and Zeeman effects. It was found that the BEC--BCS transition temperature, $T_{\mathrm{pair}}$, which corresponds to the maximum of the $Δ^*(T)$ dependence, shifts to the region of lower temperatures with increasing $B$, and the maximum value of $Δ^*(T_{\mathrm{pair}})$ decreases in fields $B > 5$~T. It was found that with increasing field, the low-temperature maximum near $T_0$ is smeared and disappears at $B > 1$~T. In addition, above the Ginzburg temperature $T_G$, for $B > 1$~T, a minimum appears on $Δ^*(T)$ at $T_{\min}$, which becomes very pronounced with a subsequent increase in $B$. As a result, the overall value of $Δ^*(T_G)$ decreases noticeably, most likely due to the pair-breaking effect. At the same time, $ΔT_{\mathrm{fl}}$ and $ξ_c(0)$ increase sharply by approximately 3 times with increasing $B$ above 1~T. Our results confirm the possibility of the formation of a vortex state in YBa$_2$Cu$_3$O$_{7-δ}$ by a magnetic field and its evolution with increasing $B$.

cond-mat.supr-con↗

arXiv2024

Evolution of the pseudogap temperature dependence in YBa$_2$Cu$_3$O$_{7-δ}$ films under the influence of a magnetic field

The evolution of the temperature dependence of pseudogap $Δ$*(T) in optimally doped (OD) YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) films with $T_{c}$ = 88.7 K under the influence of a magnetic field $B$ up to 8 T has been studied in detail. It has been established that the shape of $Δ$*(T) for various $B$ over the entire range from the pseudogap opening temperature $T$* to $T_{01}$, below which superconducting fluctuations occur, has a wide maximum at the BEC-BCS crossover temperature $T_{pair}$, which is typical for OD films and untwinned YBCO single crystals. $T$* was shown to be independent on $B$, whereas $T_{pair}$ shifts to the low temperature region along with increase of $B$, while the maximum value of $Δ$*($T_{pair}$) remains practically constant regardless of $B$. It was revealed that as the field increases, the low-temperature maximum near the 3D-2D transition temperature $T_{0}$ is blurred and disappears at $B$ > 5 T. Moreover, above the Ginzburg temperature $T_{G}$, which limits superconducting fluctuations from below, at $B$ > 0.5 T, a minimum appears on $Δ$*(T) at $T_{min}$, which becomes very pronounced with a further increase in the field. As a result, the overall value of $Δ$*(T) decreases noticeably most likely due to pair-breaking affect of a magnetic field. A comparison of $Δ$*(T) near $T_{c}$ with the Peters-Bauer theory shows that the density of fluctuating Cooper pairs actually decreases from < > $\approx$ 0.31 at $B$ = 0 to < > $\approx$ 0.28 in the field 8 T. The observed behavior of $Δ$*(T) around $T_{min}$ is assumed to be due to the influence of a two-dimensional vortex lattice created by the magnetic field, which prevents the formation of fluctuating Cooper pairs near $T_{c}$.

cond-mat.supr-con↗