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We use near-field scanning optical microscopy (NSOM) operating in collection mode to map the optical field distribution of continuous wave infrared light propagating along an air-bridged W3 silicon photonic crystal (PC) slab multimode waveguide in a subwavelength resolution. The detected near-field optical intensity distribution patterns show very different longitudinal propagation features and transverse field profiles at different wavelength ranges. We have analyzed the dispersion of the guided modes in the PC waveguide and the corresponding eigenfield profile for each guided mode by means of the three-dimensional plane-wave expansion simulations. It is found that the experimentally observed complex while interesting near-field pattern features can be well explained by the field profiles of the multiple waveguide modes and their superposition at different excitation wavelengths. The detection and analysis of this multimode PC slab waveguide via NSOM could help us to understand complex wave propagation behavior and to further design novel PC devices.

A high quality superconducting Li0.68NbO2 polycrystalline sample was prepared by deintercalation of Li ions from Li0.93NbO2. The field-dependent resistivity and specific heat were measured down to 0.5 K. The temperature dependence of the upper critical field is determined. A notable specific-heat jump is observed at the superconducting transition temperature T-c similar to 5.0 K at zero field. Below T-c, the electronic specific heat shows a thermal activated behavior and agrees well with the theoretical result for the BCS s-wave superconductor. It indicates that the superconducting pairing in Li0.68NbO2 has s-wave symmetry.

The out-of-plane resistivity (rho(c)) and magnetoresistivity (MR) are studied in antiferromangetic (AF) Nd2-xCexCuO4 single crystals, which have three types of noncollinear antiferromangetic spin structures. The apparent signatures are observed in rho(c)(T) measured at the zero-field and 14 T at the spin structure transitions, giving a definite evidence for the itinerant electrons directly coupled to the localized spins. One of the striking features is an anisotropy of the MR with a fourfold symmetry upon rotating the external field (B) within ab plane in the different phases, while twofold symmetry at spin reorientation transition temperatures. The intriguing thermal hysteresis in rho(c)(T,B) and magnetic hysteresis in MR are observed at spin reorientation transition temperatures.

In-plane (rho(ab)) and c-axis (rho(c)) resistivities and magnetoresistivity of NaxCoO2 with x=0.7, 0.5, and 0.3 and superconducting Na(0.3)CoO(2)center dot 1.3H(2)O single crystals were studied. A dimensional crossover from 2 to 3 occurs with decreasing Na concentration from 0.7 to 0.3. A striking feature is that intercalation of water leads to a reentrance of two dimensions (2D) in superconducting crystal. It suggests that the 2D plays an important role in superconductivity as the case of cuprates. The anisotropic magnetoresistivity with a d-wave-like symmetry at 2 K gives evidence for the existence of a special spin ordering like the stripes below 20 K in Na0.5CoO2.