Intermediate scattering potential strength in electron-irradiated $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-\delta}$ from London penetration depth measurements

TL;DR

This study measures how electron irradiation-induced disorder affects the London penetration depth in YBa2Cu3O7−δ, revealing a transition from linear to quadratic temperature dependence and estimating the scattering potential strength using a self-consistent t-matrix approach.

Contribution

It provides the first estimate of the scattering potential strength in electron-irradiated YBa2Cu3O7−δ using a self-consistent t-matrix theory and correlates it with changes in the density of states.

Findings

Superconducting critical temperature decreases with irradiation.

Low-temperature λ(T) shifts from T-linear to T^2 behavior after irradiation.

Estimated scattering phase shift is around 65-70 degrees.

Abstract

Temperature-dependent London penetration depth, $\lambda(T)$, of a high quality optimally-doped $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-\delta}$ single crystal was measured using tunnel-diode resonator. Controlled artificial disorder was induced at low-temperature of 20~K by 2.5 MeV electron irradiation at accumulating large doses of $3.8\times10^{19}$ and $5.3\times10^{19}$ electrons per $\textrm{cm}^{2}$. The irradiation caused significant suppression of the superconductor's critical temperature, $T_{c}$, from 94.6 K to 90.0 K, and then to 78.7 K, respectively. The low-temperature behavior of $\lambda\left(T\right)$ evolves from a $T-$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, $\rho_{s}\left(t=T/T_{c}\right)=\lambda^{2}\left(0\right)/\lambda^{2}\left(t\right)$, varying the amount and the strength of non-magnetic scattering using a self-consistent $t-$matrix theory. Fitting the obtained curves to a power-law, $\rho_{s}=1-Rt^{n}$, and to a polynomial, $\rho_{s}=1-At-Bt^{2}$, 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$^{\circ}$ and 65$^{\circ}$, respectively. We correlate this result with the evolution of the density of states with non-magnetic disorder.