Impact of oxygen annealing on the heat capacity and magnetic resonance of superconducting ${\text{Pr}}_{0.88}{\text{LaCe}}_{0.12}{\text{CuO}}_{4-\delta }$

We use thermodynamic and neutron-scattering measurements to study the effect of oxygen annealing on the superconductivity and magnetism in ${\text{Pr}}_{0.88}{\text{LaCe}}_{0.12}{\text{CuO}}_{4-\delta }$. Although the transition temperature $T_c$ measured by susceptibility and superconducting coherence length increases smoothly with gradual oxygen removal from the annealing process, bulk superconductivity, marked by a specific-heat anomaly at $T_c$ and the presence of a neutron magnetic resonance, only appears abruptly when $T_c$ is close to the largest value. These results suggest that the effect of oxygen annealing must first be determined in order to establish a Ce doping dependence of antiferromagnetism and superconductivity phase diagram for electron-doped copper oxides.

Figure 1

(Color online) (a) $T_c$ (90%) vs $\Delta$ for the same sample annealed at various temperatures in vacuum. $T_c$ (90%) is defined as the temperature where the susceptibility loses 90% of its value at 2 K. The inset shows the schematic Ce content dependence of $T_N$ and $T_c$. (b) Magnetic susceptibility of PLCCO samples with $\delta =0.034$, 0.038, 0.042, 0.047, 0.053, 0.066, 0.092 from left to right of the figure. (c) and (d) are the $\left[0.5,0.5,L\right]$ and $\left[H,H,2.2\right]$ scans through the impurity phase ${\text{R}}_2{\text{O}}_3$ peak position. The scattering intensity is normalized to a measured phonon at $Q=\left(-0.1,-0.1,6\right)$ and $T=80\text{K}$ (Ref. 26).

Figure 2

(Color online) (a) The subtracted electronic specific heat for four different samples with field $H\parallel c$. A small linear background ($<0.35\text{mJ}/{\text{K}}^2$ mole at 30 K) is also subtracted for all the samples. (b) The entropy difference between the superconducting and normal states of three different $T_c$ PLCCO. (c) The temperature dependence of $U_c$ for three different samples. (d) Temperature dependence of$C/T$. (e) $C/T$ vs $T^2$ measured on ${\text{He}}^3$ probe. (f) The residual electronic specific heat $C={\gamma }_{0}T$ at 0 K and the superconducting electronic specific heat $C={\gamma }_{\text{SC}}T$ at 0 K.

Figure 3

(Color online) Magnetic-field dependence of the superconducting heat capacity anomalies for (a) $T_c=27\text{K}$ and (b) 22 K PLCCO samples. (c) A comparison of the upper critical field $H_{c2}$ determined by specific-heat measurements for various $T_c$ PLCCO samples. $C\left(T\right)$ for $T_c=24\text{K}$ sample has already been published elsewhere (Ref. 26). For comparison, the $H_{c2}$ of the $T_c=24\text{K}$ sample obtained from resistivity is also shown. The solid linear lines are guides for the eyes.

Figure 4

(Color online) Constant $Q$ scans at $Q=\left(0.5,0.5,0\right)$ at $T=6\text{K}$ and 30 K for (a) $T_c=27\text{K}$ and (b) $T_c=21\text{K}$ PLCCO. The small peak at $\hslash \omega =6\text{meV}$ is the Pr crystal field from the “impurity” ${\text{R}}_2{\text{O}}_3$ phase which is not present in the as-grown PLCCO (Ref. 19). The corresponding differences between 6 K and 30 K are shown in (c) and (d), indicating resonance peaks. (e) and (f) show constant energy scans through $\left[H,H,0\right]$ at 6 K and 30 K near the resonance energies for these two samples.