arXiv subjects

N. V. Shytov

Publications and source records attributed to N. V. Shytov.

3 recordsLinked to original sources

arXiv2025

Study of fluctuation conductivity in YBa$_2$Cu$_3$O$_7$--$δ$ films in strong magnetic fields

We report the effect of the \emph{ab}-plane magnetic field $B$ up to $8\,\mathrm{T}$ on the resistivity $ρ(T)$ and fluctuation conductivity $σ'(T)$ in YBa$_2$Cu$_3$O$_{7-δ}$ thin films. As expected, up to $\sim 2.5\,\mathrm{T}$ the magnetic field monotonously increases $ρ$, the width of the resistive transition $ΔT_c$, and the coherence length along the $c$ axis, $ξ_c(0)$, but decreases both $T_c$ and the range of superconducting (SC) fluctuations $Δ_{\mathrm{fl}}$. The fluctuation conductivity exhibits a crossover at characteristic temperature $T_0$ from the 3D Aslamazov--Larkin (AL) theory near $T_c$ to the 2D fluctuation theory of Maki--Thompson (MT). However, at $B = 3\,\mathrm{T}$, the MT term is completely suppressed, and above $T_0$ $σ'(T)$ is unexpectedly described by the fluctuation contribution of 2D AL, suggesting the formation of a two-dimensional vortex lattice in the film under the action of a magnetic field. At the same time, $ΔT_{\mathrm{fl}}$ sharply increases by a factor of about 7, and $ξ_c(0)$ demonstrates a very unusual dependence on $T_c$ when $B$ increases above $3\,\mathrm{T}$. Our results demonstrate the possibility of the formation of a vortex state in YBCO and its evolution with increasing $B$.

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↗

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↗