S. Sarangi

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

T_{c}

Non-resonant microwave absorption studies of superconducting MgB2 and MgB2 + MgO

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

Anomalous spin dynamics in the charge-ordered two-electron doped manganiteCa0.9Ce0.1MnO3: Possibility of a spin-liquid phase

T_{c}

Charge ordering and antiferromagnetic transitions in NdxCa1−xMnO3(x=0.2,0.3) manganites

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

Experimental Evidence for Zero DC Resistance of Superconductors

T_{c}

A new behaviour of ac losses in superconducting Bi2Sr2CaCu2O8 single crystals

. 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.

Non-resonant microwave absorption studies on MgB2 thin film

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.

Studies on ac losses in Bi2SR2CaCu2O8 single crystals

Non-resonant microwave absorption (NRMA) studies of superconducting MgB2 and a sample containing ∼10% by weight of MgO in MgB2 are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB2 sample. A linear temperature dependence of the lower critical field Hc1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB2 + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links. The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB2 sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong pinning of flux lines. This hysteresis saturates a few degrees below Tc while in the MgB2 + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning.