Effect of electron irradiation on vortex dynamics inYBa2Cu3O7<

Abstract

We report on drastic change of vortex dynamics with increase of quenched disorder: for rather weak disorder we found a single vortex creep regime, which we attribute to a Bragg-glass phase, while for enhanced disorder we found an increase of both the depinning current and activation energy with magnetic field, which we attribute to entangled vortex phase. We also found that introduction of additional defects always increases the depinning current, but it increases activation energy only for elastic vortex creep, while it decreases activation energy for plastic vortex creep.PACS numbers: 74.60. Jg, 74.60.Ge, 74.60.Ec, 74.72.Bk The effect of random pinning on crystalline order and on dynamics of the flux-line-lattice (FLL) was a subject of numerous experimental and theoretical investigations. . The field H on was interpreted as a phase boundary between low field ordered and high field disordered vortex phases. These experimental results are supported by theoretical studies. It was shown that in presence of rather weak disorder the FLL retains a quasilong-range order resulting in the so-called Bragg glass phase [4]. However, with the increase of random pinning or magnetic field a transition to strongly disordered entangled vortex phase (glass phase) is predicted [5,6]. A sharp increase in magnetization below the fish-tail peak position H p was observed in N d 1.85 Ce 0.15 CuO 4−d [7] and non twinned YBa 2 Cu 3 O 7−δ [8] single crystals.Magnetic measurements showed that in optimally doped YBa 2 Cu 3 O 7−δ crystals no fishtail behavior is observed both in detwinned [9] and twinned [10] samples, while decrease of the oxygen content always induced non monotonous J m (H)-curves. Two distinctive peculiarities in the magnetization curves of oxygen deficient [10] and electron irradiated [11] crystals were observed: (1) the peaks H on and H p shift toward lower magnetic fields with increasing defect concentration, and (2) in magnetic fields H < H p the current J m increases, while in magnetic fields H > H p the current J m decreases with increasing defect concentration. It is believed [12,13] that the peak H p separates elastic vortex creep in low and plastic vortex creep, mediated by motion of the FLL dislocations, in high magnetic fields. Thus the introduction of additional defects leads to an increase of vortex pinning in the region of elastic creep and such behavior is expected. On the other hand, decrease of pinning force with increasing disorder observed in the region of plastic creep is non trivial, and reasons of such behavior are not known. The aim of this paper is to show the effect of point-like defects concentration on vortex dynamics and pinning parameters in YBa 2 Cu 3 O 7−δ single crystals.The investigated sample was YBa 2 Cu 3 O 7−δ single crystal with T c ≈ 93.5 K and ∆T c < 0.5 K. Twin planes (TP's) inside the measured part of the sample were aligned in one direction. The transport current was applied along the ab-plane and at an angle α = 45 • with respect to TP's. Measurements were performed in magnet...

Creep and depinning of vortices in a nontwinned YBa2Cu3O6.87 single crystal

“…The crossover indicates poorer adaptation of vortex lines to the pinning landscape. This leads to a decrease in the amplitude u t , and therefore to an increase in the energy [37] …”

Physicochemical methods of enhancing the performance of high-Tc superconductors

“…At present, irradiation is used as an effective means of controlling the pinning behavior of high-T c materials. A number of studies [34][35][36][37][38][39][40][41] focused on the interaction of the vortex lattice with radiationinduced defects and the phase states and phase transformations of the flux lattice.…”

Composition variation and electron irradiation effects on the fluctuation conductivity in Y1–zPrzBa2Cu3O7−δ single crystals

“…In this regard, the use of ionizing radiation has certain advantages [32]. For instance, irradiation of YBCO with fast electrons leads to a gradual increase of the electrical resistivity and a reduction of Tc without essential alteration of the oxygen stoichiometry [33]. As for the substitution of yttrium by praseodimium [34,35], it should be noted that Pr, in contrast to other RE elements, allows one to vary T c from the maximal value to zero while keeping the oxygen concentration at the optimal level [32][33][34][35][36].…”

“…For instance, irradiation of YBCO with fast electrons leads to a gradual increase of the electrical resistivity and a reduction of Tc without essential alteration of the oxygen stoichiometry [33]. As for the substitution of yttrium by praseodimium [34,35], it should be noted that Pr, in contrast to other RE elements, allows one to vary T c from the maximal value to zero while keeping the oxygen concentration at the optimal level [32][33][34][35][36]. In this way, both approaches allow one to vary the critical and electronic transport characteristics of RBa 2 Cu 3 O 7-d without affecting stability of the oxygen subsystem that is especially important from the viewpoint of their technological applications [14].…”