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

TL;DR

This study investigates how high-energy electron irradiation affects the resistivity, fluctuation conductivity, and pseudogap in YBa₂Cu₃O₇−δ single crystals, revealing complex changes in superconducting and pseudogap properties with irradiation dose.

Contribution

It provides new insights into the effects of electron irradiation on the fluctuation conductivity and pseudogap, identifying crossover points and unusual behaviors in YBCO crystals.

Findings

Irradiation causes a linear increase in resistivity and decreases T_c.

Crossover from Abrikosov–Gorkov to Emery–Kivelson behavior at a specific dose.

Pseudogap temperature and magnitude sharply increase at the crossover, then decrease with further irradiation.

Abstract

The effect of high-energy electron irradiation on the temperature dependences of the resistivity $\rho(T)$, fluctuation conductivity (FLC), and pseudogap (PG) $\Delta^{*}(T)$ of YBa$_2$Cu$_3$O$_7$--$\delta$ (YBCO) single crystals without twins was studied. Irradiation causes a linear increase in $\rho(T)$ and a decrease in the superconducting transition temperature $T_c$ with dose $\phi$. For small $\phi$, the reduction of $T_c$ follows the Abrikosov--Gorkov (AG) pair-breaking theory, while for large $\phi$ it is described by the Emery--Kivelson (EK) model, where quantum phase fluctuations dominate. At $\phi_3 = 2.5 \times 10^{19}$ e/cm$^2$, which corresponds to the AG--EK crossover, the spacing between CuO$_2$ planes $d_{01}$, the coherence length $\xi_c(0)$, 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 $\rho(\phi)$ or $T_c(\phi)$. At the same $\phi_3$, a sharp rise in the pseudogap opening temperature $T^{*}$ and in $\Delta^{*}$ indicates a possible reduction of the density of states. With further increase in $\phi$, both PG parameters and their energy scale decrease markedly, and $\Delta^{*}(T)$ acquires an unusual form. However, at $\phi_5 = 5.6 \times 10^{19}$ e/cm$^2$, the temperature dependences of FLC and PG again show behavior typical of well-structured YBCO, regardless of defect density.