Quantum spin dynamics

Abstract:

We have studied the interlayer resistivity of the prototypical quasi-two-dimensional organic superconductor κ- (BEDT-TTF)2 Cu (NCS)2 as a function of temperature, current, and magnetic field, within the superconducting state. We find a region of nonzero resistivity whose properties are strongly dependent on magnetic field and current density. There is a crossover to non-Ohmic conduction below a temperature that coincides with the two-dimensional vortex solid-vortex liquid transition. We interpret the behavior in terms of a model of current- and thermally driven phase slips caused by the diffusive motion of the pancake vortices which are weakly coupled in adjacent layers, giving rise to a finite interlayer resistance. © 2007 The American Physical Society.

Abstract:

The interlayer magnetoresistance rho(zz) of the organic metal kappa-(BEDT-TTF)(2)Cu(NCS)(2) is studied in fields of up to 45 T and at temperatures T from 0.5 to 30 K. The peak in rho(zz) seen in in-plane fields, a definitive signature of interlayer coherence, remains to Ts exceeding the Anderson criterion for incoherent transport by a factor approximately 30. Angle-dependent magnetoresistance oscillations are modeled using an approach based on field-induced quasiparticle paths on a 3D Fermi surface, to yield the T dependence of the scattering rate tau(-1). The results suggest that tau(-1) does not vary strongly over the Fermi surface, and that it has a T(2) dependence due to electron-electron scattering.

Abstract:

A range of fullerenes (C60) functionalized with long alkyl chains have been synthesized and inserted into single-walled carbon nanotubes. The impact of the alkyl chain length and of the type of linker between the addend and the fullerene cage on the geometry of molecular arrays in nanotube has been studied by high-resolution transmission electron microscopy. In the presence of functional groups the mean interfullerene separations are significantly increased by 2-8 nm depending on the length of the alkyl chain, but the periodicity of the fullerene arrays is disrupted due to the conformational flexibility of the alkyl groups.

Abstract:

Trimetallic nitride template fullerenes have been deposited onto a variety of substrates in order to elucidate the substrate-fullerene interactions. We have investigated self-assembled island formation and molecular detail of Er3N@C-80 and SC3N@C-80 on Ag/Si(111), Au(111)/mica, Si(111), and Si(001) using variable temperature scanning tunnelling microscopy (STM). At room temperature, the fullerenes self-assemble into monolayer-high hexagonal close-packed islands on Ag-passivated Si(I 1 1) whereas annealing at elevated temperatures (250-300 degrees C) is necessary for the self-assembly of close-packed islands on An(111). Intra-molecular resolution of the fullerenes has been achieved at liquid nitrogen temperature on Ag/Si(111) and already at room temperature on Si(001), when the rotation of the fullerenes is frozen. Whereas the bonding between the fullerenes and Si surfaces is mainly covalent, it appears to be mainly vander-Waals on the other surfaces. (C) 2006 Elsevier B.V. All rights reserved.

Abstract:

Trimetallic nitride template fullerenes have been deposited onto a variety of substrates in order to elucidate the substrate-fullerene interactions. We have investigated self-assembled island formation and molecular detail of Er3N@C80 and Sc3N@C80 on Ag/Si(1 1 1), Au(1 1 1)/mica, Si(1 1 1), and Si(0 0 1) using variable temperature scanning tunnelling microscopy (STM). At room temperature, the fullerenes self-assemble into monolayer-high hexagonal close-packed islands on Ag-passivated Si(1 1 1) whereas annealing at elevated temperatures (250-300 °C) is necessary for the self-assembly of close-packed islands on Au(1 1 1). Intra-molecular resolution of the fullerenes has been achieved at liquid nitrogen temperature on Ag/Si(1 1 1) and already at room temperature on Si(0 0 1), when the rotation of the fullerenes is frozen. Whereas the bonding between the fullerenes and Si surfaces is mainly covalent, it appears to be mainly van-der-Waals on the other surfaces. © 2006 Elsevier B.V. All rights reserved.