Magnetically controlled convection in a diamagnetic fluid

We present visualization and measurement of the convection of water under a high magnetic field applied vertically to the fluid. The convection was either suppressed or enhanced depending on the direction of the magnetic force. The magnetic field effect was evaluated quantitatively by measuring the onset of convection, and discussed in terms of the Rayleigh number which includes the magnetic term. The results clearly show that the convection in a diamagnetic fluid such as water can be controlled using a common 10 T class magnet.     

Thermal annealing of a-Si/Au superlattice thin films

The superlattice films, which consist of amorphous silicon (a-Si) and amorphous gold (Au), were prepared by ultra-high vacuum evaporation system. The first layer was grown a-Si with a thickness of 4.2 nm and the second layer was grown Au with a thickness of 0.8 nm. Thermal annealing was performed at 473, 673, and 873 K, respectively. The structural properties of the films were investigated using transmission electron microscope (TEM), X-ray diffraction (XRD), and Raman scattering spectroscopy. The electrical property was assessed by the temperature dependence of electrical conductivity. A crystallization of Si and a forming of Au nanoparticles were observed in all of the annealing films. The crystalline volume fraction reached 70% by annealing time for 15 min. An average diameter of the Au nanoparticles embedded in Si matrix also increased with increasing the annealing temperature. At annealing temperature above 873 K, Au atoms migrated toward the film surface. It was observed that the electrical conductivity changed in several temperatures.     

Quasiparticle picture of quarks near chiral phase transition

We study how the quasiparticle picture of the quark can be modified near but above the critical temperature (T _c) of the chiral phase transition; we incorporate into the quark self-energy the effects of the precursory soft modes of the phase transition, i.e. ‘para-σ(π) meson’. It is found that the quark spectrum has a three-peak structure near T _c: We show that the additional new spectra originate from the mixing between a quark (antiquark) and an antiquark-hole (quark-hole) caused by a “resonant scattering” of the quasi-fermions with the thermally-excited soft modes.     

Enhancement of three-dimensional electron standing waves at the metal–insulator transition in 1T-TaS2

STM images of subsurface impurities were found to change abruptly at the metal–insulator transition temperature in 1T-TaS₂. In the metallic phase the impurities were imaged as less-conducting regions with diameters less than a few nanometers; in the insulating phase, however, characteristic ring-shape structures were observed, which typically showed 1 nm in corrugation amplitude and several tens of nanometers in diameter. Based on a recent theoretical investigation, this phenomenon can be interpreted as a long-range standing wave formation caused by a significant increase of the effective wavelengths of the electronic low energy excitations associated with the metal–insulator transition.     

Morphology and orientational disorder of C70 single crystals

C₇₀ single crystals, free from solvent contamination, were grown via vapor phase transport technique. The (0001) face of the C₇₀ crystal was imaged with Atomic Force Microscopy (AFM) under ambient atmosphere. Low-resolution images of a freshly prepared crystal revealed well-ordered faceted regions with multiple terraces extending over a region of several hundred square nanometers. The terraced structure in the images indicates that the crystals formed as a layer growth. In the high-resolution images, C₇₀ molecules were resolved in a hexagonal close packed (hcp) structure with an average center-to-center distance of 10.5±0.5 Å. After one month's exposure to the ambient atmosphere, the molecules rearranged into a mixed structure consisting of hcp and face centered cubic (fcc) regions.     

NMR relaxation of 7Li in concentrated lithium-ammonia solutions

The Knight shift and the spin-lattice relaxation time of ⁷Li in lithium-ammonia solutions have been measured at -57°C over the concentration range X_Li = 0.01–0.20 (X_Li: mole fraction of Li). The Knight shift increases with increasing metal concentration, while the relaxation rate, 1/T₁, shows a broad minimum around X_Li = 0.07.     

Charge ordering and spin frustration in AlV2-x CrxO4

The relationship between charge and spin degrees of freedom in a geometrically frustrated system, AlV2-xCrxO4 spinel, is investigated. Upon Cr doping, the charge-ordered phase of AlV2O4 is rapidly suppressed and a charge-disordered phase grows up instead. It is found that the magnetic ground state is a spin-glass state dominated by geometrical frustration for both phases, but larger spin entropy remains down to low temperatures in the charge-ordered phase, possibly owing to its two-dimensional character.