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The growth of the high-T c cuprate Bi 2 Sr 2 CaCu 2 O 8 + δ (BSCCO-2212) superconductor is always challenging due to the contamination from alumina crucible or the intergrowth of other phases such as Bi 2 Sr 2 CuO 6 + δ (Bi-2201). In this work, we report the synthesis of single crystals of BSCCO-2212 with the highest reported superconducting transition temperature, T c , of 96.6 K, achieved using an improved self-flux technique. The as-grown crystals were characterized by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and powder x-ray diffraction (p-XRD) measurements. PXRD on single crystals reveals the absence of contamination from the alumina crucible as well as the absence of the intergrowth of Bi-2201 phase. PXRD on crushed single crystals reveals minimal intergrowth of Bi-2201 and Bi-2223 phases. The physical properties were investigated by carrying out temperature-dependent magnetization and resistance measurements. Magnetization measurements revealed the T c of three single crystals of BSCCO-2212 to be 93 K, 94 K, and 96.6 K, higher than the previously reported values in the range from ∼ 90 to 93 K [1-2, 3, 4–5]. Such a high T c and the absence of an intergrowth phase indicates a good quality of the grown crystals that can be utilized for fundamental as well as basic research. [ABSTRACT FROM AUTHOR]

This work reports magnetic field direction dependent second magnetisation peak (SMP) anomaly in single crystals of oxygenated for ab. Detailed investigations on crystal A revealed the direction dependence of SMP anomaly at temperatures below 25 K, above which the direction dependence vanishes. The state of spatial order of the vortex lattice was found to be correlated to the vortex lattice symmetry that underwent a change at certain fields and was captured via single flux jumps observed in the third and fifth quadrant of magnetisation hysteresis loops. Bean's critical state profiles drawn to explain the flux jumps required the presence of clusters of in the basal plane of with closely lying binding energies. Large full width at half maximum observed in Cu, O, Y and Ba photoelectron spectra confirmed the validity of the proposed cluster model. A vortex phase diagram incorporating all features in the magnetisation hysteresis loops has been made for oxygenated for || ab depicting various phases. [ABSTRACT FROM AUTHOR]

We report a systematic investigation of the differences in charge transport mechanism in ultra-thin nano-island like films of palladium with thickness varying between 5 nm and 3 nm. The thicker films were found to be metallic in a large temperature range with a dominant Bloch–Grüneisen mechanism of charge transport arising due to electron-acoustic phonon scattering. These films were also found to exhibit an additional electron–magnon scattering. At temperatures below 20 K, the two films displayed a metal-insulator transition which was explained using Al'tshuler's model of increased scattering in disordered conductors. The thinner films were insulating and were found to exhibit Mott's variable range hopping mechanism of charge transport. The thinnest film showed a linear decrease of resistance with an increase in temperature in the entire temperature range. The island-like thin films were found to display very different response to hydrogenation at room temperature where the metallic films were found to display a decrease of resistance while the insulating films were found to have an increase of resistance. The decrease of resistance was ascribed to a hydrogen induced lattice expansion in the thin films that were at the percolation threshold while the resistance increase to an increase in work function of the films due to an increased adsorption of the hydrogen atoms at the surface sites of palladium. [ABSTRACT FROM AUTHOR]

Single crystal x-ray diffraction measurements on both as-grown as well as oxygenated single crystals of an aluminium doped high temperature superconductor YBa2Cu3−xAlxO6+δ revealed the crystal structure to be orthorhombic with space group Pmmm, in contrast to, tetragonal crystal structures corresponding to space group P4/mmm, previously reported for as-grown YBa2Cu3−xAlxO6+δ, and conflicting structures on oxygenated YBa2Cu3−xAlxO6+δ. The orthorhombic crystal structure was confirmed by powder x-ray diffraction that showed the presence of two peaks corresponding to (020) and (200) reflections associated with orthorhombic structures of space group Pmmm, instead of a single (200) reflection corresponding to tetragonal crystal structures with space group P4/mmm. All the as-grown crystals were found to be superconducting. An oxygen-vacancy cluster distribution model is proposed to explain the differences in the obtained magnetisation hysteresis loop and the broad superconducting transition temperature. The model proposes the existence of two oxygen deficient clusters of (Al-..-Cu-O-Cu)n and (Cu-O-Cu-..)n juxtaposed with each other whose number and size vary as the as-grown single crystals of YBa2Cu3−xAlxO6+δ are subjected to oxygenation. X-ray photoelectron spectroscopy measurements showed the existence of two distinct peaks in each of the spectrum of O, Cu, Y and Ba in YBa2Cu3−xAlxO6+δ crystals corresponding to the two different types of clusters. The relative intensities of each XPS peak was found to decrease in the oxygenated crystals as compared to the as-grown ones confirming the change in the number and size of clusters in the as-grown crystals after oxygenation. [ABSTRACT FROM AUTHOR]

We report low-temperature magnetization measurements on a copper-containing coordination polymer [Cu( μ-C2O4)(4-aminopyridine)2(H2O)] n. According to these measurements and previous results (Prokofiev et al. in Cryst. Res. Technol. 42, 394, ), the material is a very good realization of an S=1/2 antiferromagnetic Heisenberg chain with a small saturation field B s=4.2 T, which marks the endpoint of a quantum-critical line in the B– T plane. Measurements of the magnetocaloric effect at low temperatures T=0.47 K across the saturation field yields a very large magnetothermal response with a characteristic sign change close to the quantum-critical point. The data are in good agreement with the quantum-critical behavior calculated on the basis of exact diagonalization and quantum Monte Carlo simulations. [ABSTRACT FROM AUTHOR]