Temperature-dependent London penetration depth, $\lambda \left(T\right)$, of a high quality optimally doped ${\text{YBa}}_2{\text{Cu}}_3{\text{O}}_{7-\delta }$ single crystal was measured using a tunnel-diode resonator. Controlled artificial disorder was induced at a low temperature of 20 K by 2.5 MeV electron irradiation with the accumulation of large doses of $3.8\times {10}^{19}$ and $5.3\times {10}^{19}$ electrons per ${\text{cm}}^2$. The irradiation caused significant suppression of the superconductor's critical temperature, $T_c$, from 94.6 to 90.0 K and then to 78.7 K, respectively. The low-temperature behavior of $\lambda \left(T\right)$ evolves from a $T\mathrm{linear}$ in pristine state to a $T^2$behavior after the irradiation, expected for a line-nodal $d$-wave superconductor. However, the original theory that explained such behavior had assumed a unitary limit of the scattering potential, whereas usually in normal metals and semiconductors, Born scattering is sufficient to describe the experiment. To estimate the scattering potential strength, we calculated the normalized superfluid density, ${\rho }_s(t=T/T_c)={\lambda }^2\left(0\right)/{\lambda }^2\left(t\right)$, varying the amount and the strength of nonmagnetic scattering using a self-consistent $t$-matrix theory. Fitting the obtained curves to a power law, ${\rho }_s=1-R{t}^n$, and to a polynomial, ${\rho }_s=1-At-B{t}^2$, and comparing the coefficients $n$ in one set and $A$ and $B$ in another with the experimental values, we estimate the phase shift to be around 70 and ${65}^{\circ }$, respectively. We correlate this result with the evolution of the density of states with nonmagnetic disorder.

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• Irradiation effects
• Penetration depth
• Superconductivity
• Cuprates
• High-temperature superconductors
• Superconductors