In order to enlighten the structure of vortex matter in irradiated layered Bi2Sr2CaCu2O8+δ single crystals, the interaction of Josephson vortices and pancake vortices in was investigated by means of the local ac-magnetic permeability measurements by using the miniature local coils, while vortex matter in pristine crystals was studied by in-plane resistivity measurements. The transition anomaly, separating the strong pinning phase and the weak pinning vortex phase was found by both techniques deep in the vortex solid phase solid near ab-plane, indicating crossover from the vortex chains + lattice phase to tilted vortex chains phase. While the columnar defects affect strongly the first-order vortex-lattice melting transition, the magnetic permeability anomaly, associated with the crossover from vortex chains + lattice phase to tilted lattice, is surprisingly still clear, deep in the vortex solid phase. However, the stronger columnar defects eventually affect the crossover anomaly that it disappears too.

The intrinsic Josephson junctions (IJJs) in the high-T-c superconductor Bi2Sr2CaCu2O8+delta (Bi2212) are shown to have great potential for the construction of an oscillator emitting in the terahertz-frequency f regime. However, earlier devices with Bi2212 substrates exhibit strong self-heating effects detrimental to their operation and limiting the maximum f to approximately 1 THz. Here we describe an efficient fabrication procedure for a stand-alone-mesa IJJ terahertz oscillator with considerably reduced self-heating effects, greatly expanding the tunability and maximum value of f, potentially even to 15 THz. Their typical current-voltage characteristics, radiation tunability and power, and some practical uses are also presented.

A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-Tc superconductor Bi2Sr2CaCu2O8+δ was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.

A reflection type of imaging system is shown at sub-terahertz frequencies generated from high-Tc superconducting intrinsic Josephson junction mesa structures fabricated by single crystalline Bi2Sr2CaCu2O8+δ to demonstrate how the sub-terahertz imaging technique using monochromatic radiation is powerful and unique for the variety of practical applications. Several examples are discussed in detail and are compared to other terahertz imaging systems.

In extremely anisotropic layered superconductors of Bi2Sr2CaCu2O8+delta the stacks of vortex pancakes (PV) and the Josephson vortex (JV) interpenetrate, and due to PV-JV mutual pinning energy, weakly interact and form various tilted and crossing lattice structures including vortex chains, stripes, mixed chain + lattice phases, etc. In order to study these phenomena, it is decisive to have excellent quality of samples and the ideal experimental techniques. The vortex phases in high-quality Bi2Sr2CaCu2O8+delta single crystals were studied by in-plane resistivity measurement and local ac magnetic permeability. The sharp crossover was shown by both techniques, deep in the vortex solid state separating the Abrikosov dominant 'strong pinning' phase from the Josephson dominant 'weak pinning' phase. Those two vortex states were recognized as the mixed chain + lattice vortex phase and chains (tilted) vortex phase, respectively. (C) 2012 Elsevier B. V. All rights reserved.

In order to investigate the interaction between Josephson vortices and pancake vortices in a layered Bi2Sr2CaCu2O8+δ superconductor, c-axis resistivity measurements were carried out on fabricated mesoscopic single crystals for two experimental geometries, when an applied high magnetic field of 14 T is perpendicular (Bex⊥L) and parallel (Bex∥L) to the width of sample. In the first case, the angular dependence of the resistance obtained near the ab-plane at T=30K exhibited hysteretic non-monotonic behavior with local maxima at θ=0.6° away from the ab-plane and dips and spikes at θ=0.2° marking a vortex lock-in transition. In the second geometry (Bex∥L), instead of a local maximum, peculiar resistance shoulders were observed. At higher temperatures, hysteresis is reduced, while the vortex lock-in transition becomes considerably broader indicating the interaction of pancake and Josephson vortices.

Vortex matter of the mesoscopic Bi2Sr2CaCu2O8+δ single crystal has been studied in high magnetic fields near its ab-plane by using the c-axis resistivity measurements. While the dependence Rc(H) increases gradually with the intensity of the magnetic field parallel to the ab-plane and exhibits the oscillations, in magnetic fields tilted slightly away from the ab-plane, the magnetic field dependence of the resistance showed a local maximum. The observed behavior can be attributed to the pancake-vortex pinning.

The c-axis resistivity measurements were performed in the vicinity of the ab-plane in order to investigate the interaction between Josephson vortices and pancake vortices in Bi2Sr2CaCu2O8+δ mesoscopic single crystals. It was found that the angular dependence of the c-axis resistivity drastically changes in high magnetic field regime. The vortex lock-in transition becomes considerably broad in high magnetic fields, while the angular dependence of resistance exhibits the sharp lock-in features in low magnetic field region.

Vortex matter of the layered superconductors in very high magnetic fields near the ab-plane was studied by using the c-axis resistivity measurements on the mesoscopic Bi2Sr2CaCu2O8+δ single crystals. While the angular dependence of resistance exhibits the sharp lock-in features in low magnetic field region, it was found that the vortex lock-in transition becomes considerably broad in high magnetic fields, showing anomalous shoulders at 0.3° away from the ab-plane. The appearance of the resistance shoulder is followed with the stronger current level dependence, indicating possible different phases due to interplay of Josephson vortices and pancake vortices near ab-plane.