Possible competitive electron- and hole-like conduction in the revived Nd1.82Ce0.18CuOy superconductors

The paramagnetic Meissner effect in superconductors at 40 G and flux trapping

“…These features are not visible in the x = 0.145 sample, indicating its inferior quality. It is also clear from the figure that the T c decreases with increase in x beyond these compositions (see the phase diagram in[15] for comparison). The figure further reveals that the FC χ displays negative values (i.e.…”

“…We, therefore, believe that present explanation based on the local oxygen variation is equally applicable in other HTSCs wherein oxygen variation is always expected in real samples. It is clear from the above argument that for the samples with PME or at the threshold of exhibiting PME, the Meissner effect is expected to be partial as was observed in NCCO samples in particular and HTSCs in general [1][2][3]15]. Further, the PME observed at 40 G seemingly correlates with the presence of more prominent local oxygen variation compared to other HTSCs because of the reduction step required.…”

“…To test this, samples of nominal compositions x = 0.145, 0.150, 0.155 and 0.165 were synthesized by a standard solid state reaction method. The details of the preparation procedure are given elsewhere [15]. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements were made on approximately tapered parallelepiped pellets using a vibrating sample magnetometer (VSM, Oxford Instruments, model VSM 3001) in the temperature range 1.8-30 K. The tapered pellet effectively reduces the demagnetization factor and possible PME due to random shape [11,12,16].…”

X-ray absorption near edge structure study of -type revived superconducting compounds, (NACCO), A = Ca, Sr or Ba,

“…The electron doped T -type Ln 2−x Ce x CuO 4 (Ln = Nd, Pr, Sm, Eu) superconducting (SC) system has continued to be the subject of considerable interest [1][2][3][4][5][6][7][8][9][10][11][12][13] ever since its discovery by Tokura et al [1]. It is observed that in the reduced Nd 2−x Ce x CuO y (NCCO) compounds, superconductivity is exhibited in a narrow range of Ce concentration, 0.14 ≤ x < 0.18, and T c is completely suppressed at x = 0.18 [14]. Superconductivity which disappears in Ce excess Nd 1.82 Ce 0.18 CuO 4.09 has been revived [15] through substitution of the divalent alkalineearth (A = Ca, Sr or Ba) ion in appropriate concentration (0.06 ≤ z ≤ 0.18).…”

The interrelationship of Cu effective charge and superconductivity in the T´-type Gd1.85-xPrxCe0.15CuOysystem

“…In high temperature cuprate superconducting (SC) systems, the content of ordered lattice oxygen manifests the important role it plays in affecting the value of critical temperature (T c ) in a given compound [1][2][3][4][5][6][7]. It is now almost an accepted view that a critical level of carrier doping of Cu-O planes, via charge transfer, is essential, besides other factors, for a layered cuprate to exhibit superconductivity [8][9][10][11][12][13][14].…”