W. Jiang

Measurements of vortex-transport entropy in epitaxial Nd1.85Ce0.15CuO4−σ films evidence for quasiparticle bound state quantization in the vortex core

Abstract We report measurements of the vortex-transport entropy in the high-temperature superconductor Nd 1.85 Ce 0.15 CuO 4− σ . The vortex transport entropy, determined from flux-flow Nernst effect and resistivity measurements, is about 100 times smaller than Makis theoretical prediction. Using a simple microscopic model, we show that the entropy decrease is a result of the large energy level spacing between quasiparticle bound states in the vortex core, providing strong evidence for the discreteness of these states.

Unusual properties of Nd1.85Ce0.15CuO4±δ with varying oxygen concentration

Abstract We have studied in detail the in-plane transport properties of Nd 1.85 Ce 0.15 CuO 4±δ (NCCO) films and crystals over a wide range of oxygen concentration. We find that the appearance of superconductivity strongly correlates with a positive magnetoresistance in the normal state as well as a positive component to the negative Hall coefficient. Together with our observation of an anomalously large discrepancy between the Hall angle obtained from the Hall effect and resistivity and that obtained from the Nernst and Seebeck effects, our data provide strong evidence for the existence of hole and electron carriers in this “electron-doped” superconductor.

In-plane transport properties of single-crystal Nd2−xCexCuO4

Abstract We report in-plane transport properties of high-quality Nd 2− x Ce x CuO 4 crystals prepared over a range of Ce doping x. The thermopower S and the negative Hall coefficient R H observed for superconducting and low- x compositions indicate that the dominant charge carriers in the CuO 2 planes are n-type. The negative and highly anisotropic magnetoresistance in low- x crystals is strong evidence for a weakly localized electronic state at low T .

Radiation damage effects in Nd2−xCexCuO4−y thin films

Abstract We report on the effect of 4 MeV alpha-irradiation on the transition temperature T c and critical current density j c of Nd 2− x Ce x CuO 4− y (NCCO) thin films. The same dependence of T c and j c on the defect energy deposition is found for NCCO as for other irradiated cuprates, and is independent of large differences in the maximum T c . The results strongly suggest that apical oxygen atom displacements do not contribute to the strong reduction of T c , and that the main mechanism for T c reduction is a depairing-like variation.

Preparation and properties of superconducting Bi2Ca3-xRxCu2O8+δ

Abstract Several materials of the general composition Bi 2 Ca 3- x R x Cu 2 O 8+ δ ( R = Pr , Nd , Sm , Eu Gd ) have been synthesized by a three-step process. Within a narrow range of composition ( x ∼0.5), the samples are almost single phase possesing a pseudo-tetragonal structure similar to Bi 2 Sr 2 CaCu 2 O 8 . Maximum onset temperature for bulk superconductivity is about 60 K for R = Pr , Nd and Sm as determined by DC magnetization experiments. T c decreases to about 30 K for R + Eu , Gd. The oxygen stoichiometry is demonstrated to play an important role in the superconducting properties. Thermogravimetric analysi and Hall effect measurements reveal that these compounds have smaller hole densities compared with Bi 2 Sr 2 CaCu 2 O 8 and that Pr ions might be in a mixed-valence state between 3+ and 4+ in the compound Bi 2 Ca 2.5 Pr 0.5 Cu 2 O 8+δ .

Optical response of superconducting Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ and YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films

The normal state and transition edge optical response of epitaxial thin films of n-type superconductor Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/ has been measured. In contrast to the optical response of p-type superconductors such as YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// the normal state optical response of these films were not proportional to the temperature derivative of the resistance. The normal state optical response of films with different transition temperature (and, therefore, different oxygen content) were also remarkably different from each other. We attribute the observation of anomalous optical response to the possible presence of photoconductivity in Nd/sub 1.85/Ce/sub 0.15/CuO/sub 4-y/. We also discuss the feasibility of fabricating bolometers based on superconducting p-n bilayers.<<ETX>>