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.     

Development of new WC–Ni hardmetals for use in high pressure experiments

Ultrafine-grained (0.2–0.3?µm) WC–Ni hardmetals with a low Ni content (3–5?wt%) were developed using new production techniques based on adding an appropriate amount of VC and Cr₃C_2, combined with the strong mixing of raw materials. Their uniaxial compressibility was subsequently compared with that of existing WC–Ni and WC–Co hardmetals to assess their suitability for use as anvils in various high pressure experiments, particularly those associated with neutron or magnetic studies. The ultimate compressive strength of the newly developed hardmetals was over 7.7?GPa, which was higher by 1.2?GPa than that of the existing WC–Ni hardmetal ‘MF10’. When these hardmetals were used as anvils, a pressure of approximately 16?GPa was generated using a Paris-Edinburgh-type apparatus with φ8?mm culet, thereby proving that they can allow the physical properties of various materials to be measured at higher pressures than is possible with existing hardmetals.     

A simple opposed-anvil apparatus for high pressure and temperature experiments above 10 GPa

A new opposed-anvil high pressure and temperature apparatus was developed based on the Drickamer-type apparatus. Various improvements were made to increase the sample volume and to generate high pressure and temperature stably and easily. By optimizing components such as the anvil, heater, and gasket, large sample volumes of about 4?mm³ (～10³ times more than that previously obtained with our previous apparatus) were achieved, with compact and light apparatus (outer diameter ? 40?mm; height 31?mm; weight 300?g). Pressures and temperatures up to about 15?GPa and 1700?K can routinely and stably be achieved by using this assembly. In order to extend the pressure range further, sintered diamond was used as an anvil material. As a result, pressures and temperatures of around 38?GPa and 1400?K were achieved, although the sample volume was decreased to about 1.3×10^?1?mm³.     

Performance of ceramic anvils for high pressure neutron scattering

Three kinds of ceramics, zirconia-toughened alumina (ZTA), alumina-toughened zirconia (ATZ) and yttria-stabilized zirconia (YSZ), were tested as anvil materials, mainly for the purpose of neutron scattering study under high pressure. ZTA with non-toroidal anvil profile, having the same sample volume as conventionally used double toroidal anvils, sustained pressures up to 11.9?GPa. This is comparable to anvils made of tungsten carbide (TC) with Ni binder with the same dimensions. ATZ would also be an alternative material to TC with pressure performance comparable to ZTA, whereas YSZ is much weaker than the other two ceramics. The attenuation coefficient for YSZ is significantly smaller than that of TC and similar to ZTA and ATZ, the latter being estimated by attenuation calculations. Neutron diffraction on a sample of lead in YSZ anvils as well as quasi-elastic neutron scattering on liquid water in ZTA also demonstrate the outstanding neutron transparency of these ceramics. The gain factor in count rate is up to one order of magnitude.     

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.