Heat Treatment Effects on the Superconductivity and Crystal Structure of Nd_1.85Ce_0.15CuO₄Studied Using a Single Crystal

Microscopic annealing process and its impact on superconductivity in T′-structure electron-doped copper oxides

“…Experimentally, it was found that about 1%~2% of the impurity phase, absent in the as-grown materials, appears with superconducting phase after the oxygen reduction process [18][19][20][21] . Although not explicitly demonstrated, the R 2 O 3 impurity phase may disappear again when annealed samples are oxygenated to eliminate superconductivity 15,21 . Therefore, superconductivity in electron-doped materials might be intimately related to the appearance of the impurity phase.…”

“…), electron-doping alone is insufficient, and annealing the as-grown sample in a low oxygen environment to remove a tiny amount of oxygen is necessary to induce superconductivity 2,3 . Previous work [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] suggests that oxygen reduction may influence mobile carrier concentrations 7 , decrease disorder/impurity scattering 8,10,11,23 , or suppress the long-range AF order 16,17,22 . However, the microscopic process of oxygen reduction, its effect on the large electron-hole phase diagram asymmetry and mechanism of superconductivity 2,3 are still unknown.…”

“…5%) entirely suppress AF order and superconductivity appears over a wide range of hole concentrations (from 6% to 30%). In the case of T' structured electron-doped superconductors, doping alone by substituting the trivalent ions R 3+ in R 2 CuO 4 with tetravalent Ce 4+ is insufficient to induce superconductivity and the as-grown materials such as Nd 2-x Ce x CuO 4±δ (NCCO), Pr 2-x Ce x CuO 4±δ (PCCO), and Pr 0.88 LaCe 0.12 CuO 4 (PLCCO) are semiconducting with static long-range AF order [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] .In these materials, superconductivity (maximum T c ~25 K) is achieved only when the samples within a relatively narrow dopant range (0.1≤x≤0.18) are annealed in a reducing atmosphere . The reduction process suppresses the AF order most severely at higher Ce-doping levels above x≥0.1 (ref.…”

“…31) have recently determined the Fermi surface topology and the superconducting gap function in electron-doped materials. However, the quality of the sample surfaces studied has not been conclusively established, and one must now consider the possible effect of an exposed NSC R 2 O 3 surface in future ARPES and scanning tunneling microscopy experiments.Furthermore, it should also be possible to grow higher-quality single-crystal T' structured copper oxides by adding excess Cu in the starting materials to eliminate Cu deficiencies and subsequent R 2 O 3 contamination.Because of the availability of single crystals of the T' structured copper oxides, the vast majority of transport, structural, magnetic, and electronic-property measurements of electron-doped superconductors have been obtained from these materials [9][10][11][12][13][14][15][16][17][18][19][20][21][22]25,[27][28][29][30][31] . For other electron-doped high-T c superconductors with different crystal structure types, such as the infinite-layer Sr 1-x La x CuO 2 family 32-34 , the microscopic process of inducing superconductivity is still unclear 33,34 .…”

Square Vortex Lattice at Anomalously Low Magnetic Fields in Electron-DopedNd1.85Ce0.15CGilardi1, Mesot2, Brown3 et al. 2004Phys. Rev. Lett.

“…Crystals of NCCO were grown in a mirror furnace and annealed as described in ref. [27] to give an onset T c ≈ 25 K (∆T c ≈ 3 K, 10%-90% criterion). Samples with two shapes were investigated in applied magnetic fields up to 0.4 T. In high fields, a cylinder of 5 mm diameter, consisting of two nearly aligned crystals, was mounted in a cryostat with the magnetic field direction bisecting the two c-directions and at 7 • to each of them.…”