Annealing effect on the electron-doped superconductor ${\text{Pr}}_{0.88}{\text{LaCe}}_{0.12}{\text{CuO}}_{4\pm \delta }$

Using high-vacuum annealing treatment, the superconducting transition temperature $T_c$ of the electron-doped ${\text{Pr}}_{0.88}{\text{LaCe}}_{0.12}{\text{CuO}}_{4\pm \delta }$ single crystals was successfully driven to a regime in which the $T_c$ value continuously decreases with oxygen removal. This regime of oxygen-reduction process is hard to be understood according to the previous knowledge of this material. In addition, a remarkable relaxation of $T_c$ over time was observed at room temperature, indicating that the variation in $T_c$ is closely related to the rearrangement of oxygen in the sample. In combination with previous studies, it can be concluded that, in the whole process of oxygen reduction applied on ${\text{Pr}}_{0.88}{\text{LaCe}}_{0.12}{\text{CuO}}_{4\pm \delta }$, although the strength of antiferromagnetic (fluctuation) correlations does play a role, $T_c$ is dominated by the disorder effect of ${\text{CuO}}_2$ plane either on copper sites or oxygen sites, which leads to a strong depairing effect.

Figure 1

(Color online) Crystal structure of $R{E}_{2-x}{\text{Ce}}_x{\text{CuO}}_{4\pm \delta }$. Three oxygen are denoted: O(1) in the ${\text{CuO}}_2$ plane, O(2) in the REO layer ($RE=\text{Pr},\text{La}$ in this paper), and a tiny amount of O(3) in the apical site.

Figure 2

(Color online) $T_c$ evolution (indicated by ac susceptibility) with oxygen reduction in annealing processes, the increasing indexes indicate a decreasing of oxygen content. [(a) and (b)] UA regime: $T_c$ increases with oxygen removal at different annealing temperatures (Table ). (c) A continuous oxygen-reduction process from UA or $T_c$-increasing regime to OA or $T_c$-decreasing regime. (d) OA regime: $T_c$ decreases with oxygen removal. The dashed lines in (c) and (d) denote the highest $T_c$ got on the corresponding samples.

Figure 3

(Color online) $T_c$ versus oxygen reduction. The solid arrow lines indicate the direction of annealing process and the dot arrows indicate the direction of relaxing process. The horizontal axis data is in an arbitrary unit since the real oxygen content is hard to be obtained.

Figure 4

(Color online) (a) Superconducting transitions of the same sample measured at two different times with an interval of almost ten months. [(b) and (c)] $T_c$ relaxations at OA and UA regimes, respectively. (d) Oxygenated process in atmosphere.

Figure 5

(Color online) $T_c$ relaxations in OA regime. Samples S1 and S2 were cut from the same sample and stored in vacuum and atmosphere, respectively. The curves are normalized for comparing.

Figure 6

(Color online) Change in resistivity $\rho$ accompanied by the $T_c$ relaxation in the OA regime. (a) Temperature dependence of resistivity at various fields before and after relaxation. (b) The normalized resistivity by the value of 100 K, the inset shows the data of 9 T.

Figure 7

(Color online) Change in Temperature dependence of Hall coefficient $R_H$ accompanied by the $T_c$ relaxation in the OA regime. The insets show the field dependence of Hall resistivity ${\rho }_{xy}$ at various temperatures before and after relaxation, respectively.