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This work presents a simple and quick method to define unambiguously the orientation of the a and b crystallographic axes in an untwinned domain of single crystals. The method is based on the analysis of the light reflected on such a domain, for normally incident light selected in the red spectral range. Micro-Raman scattering measurements, which are another way to attribute the crystalline axes, have been investigated to confirm the orientation of the a and b axes by polarization microscopy.

A new technique to probe a single nanometer-scale magnetic particle by measuring the tunneling current through point-contact electrodes is described. The tunnel junctions are formed by a bulk cobalt bottom electrode, a monolayer of ultrasmall Co clusters sandwiched between two Al2O3 barriers and a point-contact top electrode, defined by e-beam lithography and permitting to study the quantum transport through an isolated cluster. We report on single electron charging effects such as Coulomb blockade and Coulomb staircase which are undoubtedly consistent with the tunneling through a single Co cluster. One of our devices exhibits a Coulomb gap of 380 mV which is, to our knowledge, one of the largest values ever reported in metallic granular systems.

This work presents a simple and quick method to define unambiguously the orientation of the a and b crystallographic axes in an untwinned domain of YBa 2 Cu 3 O 7-δ (δ→0) single crystals. The method is based on the analysis of the light reflected on such a domain, for a normal incident light selected in the red spectral range.