Quantum spin dynamics

Abstract:

We report high-field magnetotransport measurements on β″-(BEDT-TTF)4[(H3O)M(C2O4)3]Y, where M = Ga, Cr, and Fe and Y = C5H5N. We observe similar Shubnikov-de Haas oscillations in all compounds, attributable to four quasi-two-dimensional Fermi-surface pockets, the largest of which corresponds to a cross-sectional area 8.5% of the Brillouin zone. The cross-sectional areas of the pockets are in agreement with the expectations for a compensated semimetal, and the corresponding effective masses are me, rather small compared to those of other BEDT-TTF salts. Apart from the case of the smallest Fermi-surface pocket, varying the M ion seems to have little effect on the overall Fermi-surface topology or on the effective masses. Despite the fact that all samples show quantum oscillations at low temperatures, indicative of Fermi liquid behavior, the sample and temperature dependence of the interlayer resistivity suggest that these systems are intrinsically inhomogeneous. It is thought that intrinsic tendency to disorder in the anions and/or the ethylene groups of the BEDT-TTF molecules leads to the coexistence of insulating and metallic states at low temperatures. A notional phase diagram is given for the general family of β″-(BEDT-TTF)4[(H3O)M(C2O4)3]Y salts. © 2004 The American Physical Society.

Abstract:

A clear understanding of the interactions between the building blocks of self-assembled molecular materials is essential for rational design of functional nanostructures. Intermolecular interactions have been investigated for three different classes of fullerenes in single-walled carbon nanotubes (SWNTs); van der Waals molecule - molecule and molecule - SWNT interactions control the geometry of the molecular arrays inside nanotubes; electrostatic intermolecular forces influence the alignment of polar endohedral fullerenes M@C82; and hydrogen bonding between functionalised fullerenes has a significant effect on the selectivity of insertion of functionalised fullerenes into SWNTs.

Abstract:

Exohedrally functionalised fullerenes have been inserted in single-walled carbon nanotubes (SWNTs) with the aid of supercritical carbon dioxide to form peapods; C61(COOEt)2 are encapsulated in SWNTs in high yield, whereas C61(COOH)2 aggregate via hydrogen bonding to form a supramolecular complex, which sterically hinders encapsulation and causes it to adhere to the exterior surface of the SWNTs. © 2004 The Royal Society of Chemistry.

Abstract:

We describe the Polarization Synchrotron, an experimental implementation of a superluminal (faster than light in vacuo) polarization current distribution that both oscillates and undergoes centripetal acceleration. The prototype machine produces tightly-beamed monochromatic radiation in the 100s of MHz range. The technique should also have applications as a broad-band GHz-THz source.