Spin dynamics in the Cu(2)-O planes of tetragonal and orthorhombic YBa2Cu3O7-delta as probed by 89Y NMR

The 89Y-nuclear relaxation rate is found to be almost similar in the orthorhombic and tetragonal modifications of YBa2Cu3O7-d. This result is seen as evidence for the unchanged spin dynamics in the Cu(2)-O planes in both compounds and as support for those theories that decouple charge and spin carriers

The conductivity and band structure of some synthetic semiconductors based on M(dmit)2 (M = Ni, Pd, Pt)

The conductivity of the following six new low-dimensional compounds is reported: (Me4N)(Ni(dmit)2), (Et4N)(Ni(dmit)2), (Pr4N)(Ni(dmit)2), (Bu4N)(Ni(dmit)2), (Bu4N)(Pt(dmit)2) and (Et4N)0.5(Pd(dmit)2). Semiconducting behaviour is found for all the compounds investigated, with activation energies between 0.1 and 0.5 eV. The crystal structures have been established by X-ray diffraction. Using these, the band structure has been determined. It is shown that the compounds investigated are semiconductors each having a correlation gap resulting from an effective electron-electron repulsion of 1.0 eV

Measurement of the complex dielectric constant down to helium temperatures. I. Reflection method from 1 MHz to 20 GHz using an open ended coaxial line

Metals in Catalysis, Biomimetics & Inorganic Material

Understanding the doping dependence of the conductivity of conjugated polymers: dominant role of the increasing density of states and growing delocalization

In variable-range-hopping theories for the dc conductivity, the extension of sites where the charges are located and the energy dependence of the density of states (DOS) are usually neglected. We show that these dependences are the dominant factors for understanding the strong doping dependence, and present an analytical theory for arbitrary DOS. We verify the theory with systematic data over a broad range of temperature and doping for FeCl3-doped poly(p-phenylene vinylene). By combining theory and data, we reconstruct the energy-dependent DOS and the extension of sites

Quantum tunnelling of magnetization in Mn12-ac studied by 55Mn NMR

We present an ultra-low temperature study (down to T = 20 mK) of the nuclear spin-lattice relaxation (SLR) in the 55Mn nuclei of the molecular magnet Mn12-ac. The nuclear spins act as local probes for the electronic spin fluctuations, due to thermal excitations and to tunnelling events. In the quantum regime (below T = 0.75 K), the nuclear SLR becomes temperature-independent and is driven by fluctuations of the cluster's electronic spin due to the quantum tunnelling of magnetization in the ground doublet. The quantitative analysis of the nuclear SLR shows that the presence of fast-tunnelling molecules, combined with nuclear intercluster spin diffusion, plays an important role in the relaxation process.Comment: RevTex, 5 pages, 3 eps figures; presented at the Internation Conference on Molecular Magnets (Valencia, 5 - 10 Oct. 2002); to be published in Polyhedro

Measurement of the complex dielectric constant down to helium temperatures. II. Quasi-optical technique from 0.03 to 1 THz

Metals in Catalysis, Biomimetics & Inorganic Material