Influence of electron irradiation on fluctuation conductivity and pseudogap in YBa2Cu3O7−δ single crystals

Abstract

The effect of electron irradiation with the energy of 2.5 MeV on the temperature dependences of the resistivity ρ( T) of an optimally doped YBa2Cu3O7−δ single crystal has been studied. The temperature dependences of both fluctuation conductivity σ′ ( T) and the pseudogap Δ*( T) on irradiation dose φ have been calculated within the local pair model. Here we show that with an increase in φ, the value of ρ(300 K) increases linearly, while Tc decreases linearly. Concurrently, the value of ρ(100 K) increases nonlinearly, demonstrating a feature for φ3 = 4.3⋅1018 e/cm2, which is also observed in the number of other dose-dependent parameters. Regardless of the irradiation dose, in the temperature range from Tc up to T01, σ′( T) obeys the classical fluctuation theories of Aslamazov-Larkin (3D-AL) and Maki-Thompson (2D-MT), demonstrating 3D-2D crossover with increasing temperature. The crossover temperature T0 makes it possible to determine the coherence length along the c axis, ξ c(0), which increases by ∼3 times under irradiation. Furthermore, the range of superconducting fluctuations above Tc also noticeably increases. At φ1 = 0, the dependence Δ*( T) typical for single crystals containing pronounced twin boundaries is observed with a maximum at Tpair ∼120 K and a distinct minimum at T =  T01. It was determined for the first time that at φ3 = 4.3⋅1018 e/cm2 the shape of Δ*( T) changes strongly and becomes the same as in optimally doped YBa2Cu3O7−δ single crystals with a very low pseudogap opening temperature T* and noticeably reduced Tpair, while at Tc(φ) there are no singularities. With an increase in the irradiation dose up to φ4 = 8.81018 e/cm2, the shape of Δ*( T) is restored and becomes the same as in well-structured YBa2Cu3O7−δ films and untwined single crystals. Moreover, in this case, Tpair and T* increase noticeably.