S. P. Chockalingam

Fabrication of cerium-doped LaNiO3 thin films on LaAlO3 (100) substrate by pulsed laser deposition

In this study we report the fabrication of La 1−x Ce x NiO 3 (0≤x≤0.4) thin films on a LaAlO 3 (100) substrate by pulsed laser deposition where the cerium ions are believed to be in the Ce (IV) oxidation state. At low Ce concentrations, the films grow in the (100) direction with a pseudocubic structure and above x~0.3, they exhibit a change in the crystal symmetry. Core-level photoelectron spectroscopic studies of the thin films deposited have shown that the cerium exists in the +4 oxidation state. Correspondingly, the nickel exhibits mixed valency in these thin films. Conductivity of this highly metallic system progressively decreases as more and more Ce is doped. In the range 0.3 1−x Ce x NiO 3 thin films gives clear indications of significant electron-lattice interactions present for compositions close to the transition.

Frequent Josephson junction decoupling is the main origin of ac losses in the superconducting state

The origins of ac losses in the high

Equipartition of current in parallel conductors on cooling through the superconducting transition

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Experimental Evidence for Zero DC Resistance of Superconductors

superconductors are not addressed adequately in the literature. We found out that frequent Josephson junction (JJ) decoupling (both intergranular and interlayer) due to the flow of ac is one of the main origins of the ac losses in high

A new behaviour of ac losses in superconducting Bi2Sr2CaCu2O8 single crystals

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Studies on ac losses in Bi2SR2CaCu2O8 single crystals

superconductors. We have determined the ac losses in superconductors in the rf range by measuring the absolute value of nonresonant rf power absorbed by the samples. Our data show that under certain conditions when both the number density of JJs present in the sample and the JJ critical current cross a threshold value, ac losses in the superconducting state keep on increasing with decreasing temperature below

Magnetic field dependent direct rf power absorption studies in Bi_2 Sr_2 CaCu_2 O_8 single crystals

T_{c}

Josephson junction decoupling is the main origin of AC resistivity in the superconducting state

. The underlying mechanism is an interesting interplay of JJ coupling energy and the amplitude of rf voltage applied to the sample. The effects of an applied magnetic field, variation of rf, and temperature were studied in detail. To find out the exact relation among the JJ coupling energy, JJ number density, applied ac frequency, the amplitude of ac, and the ac losses in superconductors, we have studied samples with different crystalline properties, different grain sizes, pressurized at different pressures, and sintered under different physical and chemical conditions. These results have important implications for the understanding of the origin of ac losses and the characterization of superconducting samples. In this paper we also extend the capability of the ac loss studies in superconductors for the characterization of materials for device applications.

Angular dependence of direct rf power absorption studies in Bi2Sr2CaCu2O8 single crystals

Our experiments show that for two or more pieces of a wire, of different lengths in general, combined in parallel and connected to a dc source, the current ratio evolves towards unity as the combination is cooled to the superconducting transition temperature T c , and remains pinned at that value below it. This redistribution of the total current towards equipartition without external fine-tuning is a surprise. It can be physically understood in terms of a mechanism that involves the flux-flow resistance associated with the transport current in a wire of type-II superconducting material. It is a fact that the flux-flow resistance increases with the current that drives the current division towards equipartition.