M A Alam

Nesting Properties and Anisotropy of the Fermi Surface of LuNi{sub 2}B{sub 2}C

The rare-earth nickel borocarbides, with the generic formula RNi{sub 2}B {sub 2}C , have recently been shown to display a rich variety of phenomena. Most striking has been the competition between, and even coexistence of, antiferromagnetism and superconductivity. We have measured the Fermi surface (FS) of LuNi{sub 2}B {sub 2}C , and shown that it possesses nesting features capable of explaining some of the phenomena experimentally observed. In particular, it had previously been conjectured that a particular sheet of FS is responsible for the modulated magnetic structures manifest in some of the series. We report the first direct experimental observation of this sheet. (c) 1999 The American Physical Society.

Observation of a Strongly Nested Fermi Surface in the Shape-Memory Alloy Ni 0.62 Al 0.38

The Fermi surface topology of the shape-memory alloy Ni0.62Al0.38 has been determined using Compton scattering. A large area of this Fermi surface can be made to nest with other areas by translation through a vector of approximately 0.18[1,1,0](2pi/a), which corresponds to the wave vector associated with martensitic precursor phenomena such as phonon softening and diffuse streaking in electron diffraction patterns. This observation is compelling evidence that these phenomena are driven by the enhanced electron-lattice coupling due to the Fermi surface nesting.

Phase transitions of CO2 confined in nanometer pores as revealed by positronium annihilation

The results of a comprehensive positronium annihilation study of the phase behaviour of carbon dioxide in porous Vycor glass are presented. Isobaric measurements of the 3 gamma :2 gamma annihilation ratio show that on cooling, the gas-liquid phase boundary is raised by ~5 K while the liquid-solid transition is depressed by ~12 K relative to the bulk. The resulting phase diagram suggests the existence of a `triple point` of the confined fluid at a temperature ~10 K and a pressure ~2 bar below the bulk triple point.

A nanostructural investigation of glassy gelatin oligomers: molecular organization and interactions with low molecular weight diluents

The effects of low molecular weight diluents (namely water and glycerol) on the nanostructure and thermodynamic state of low water content gelatin matrices are explored systematically by combining positron annihilation lifetime spectroscopy (PALS) with calorimetric measurements. Bovine gelatin matrices with a variation in the glycerol content (0?10?wt.%) are equilibrated in a range of water activities (aw?=?0.11?0.68, T?=?298?K). Both water and glycerol reduce the glass transition temperature, Tg, and the temperature of dissociation of the ordered triple helical segments, Tm, while having no significant effect on the level of re-naturation of the gelatin matrices. Our PALS measurements show that over the concentration range studied, glycerol acts as a packing enhancer and in the glassy state it causes a nonlinear decrease in the average hole size, vh, of the gelatin matrices. Finally, we report complex changes in vh for the gelatin matrices as a function of the increasing level of hydration. At low water contents (Qw???0.01?0.10), water acts as a plasticizer, causing a systematic increase in vh. Conversely, for water contents higher than Qw???0.10, vh is found to decrease, as small clusters of water begin to form between the polypeptide chains.

Fermi surface nesting and charge-density wave formation in rare-earth tritellurides

The Fermi surface of rare-earth tritellurides

Fermi surface as the driving mechanism for helical antiferromagnetic ordering in Gd-Y alloys

(R{\mathrm{Te}}_{3})

Positron annihilation study of the Fermi surface of Ni2MnGa

is investigated in terms of the nesting-driven charge-density wave formation using positron annihilation and first-principles linear muffin-tin orbital calculations. Fermi surface nesting is revealed as a strong candidate for driving charge-density wave formation in these compounds. The nesting vector obtained from positron annihilation experiments on

Spin density in Gd studied by magnetic Compton scattering

{\mathrm{GdTe}}_{3}

Effect of crystallization and of water uptake on the free-volume hole size in polyamides 6 and 66

is determined to be

A nano-scale free volume perspective on the glass transition of supercooled water in confinement

\mathbf{q}=(0.28\ifmmode\pm\else\textpm\fi{}0.02,0,0){\mathbf{a}}^{*}