Observation of local atomic displacements intrinsic to the double zigzag chain structure of 1T-MTe2 (M = V, Nb, Ta)

We describe the existence of local distortion discovered in the synchrotron x-ray single-crystal structure analysis of layered ditelluride 1T-MTe2 (M = V, Nb, Ta). In 1T-TaTe2, the double zigzag chain structure of Ta is deformed at about 170 K, and heptamer molecules are formed periodically at low temperatures. We found that some of the Ta atoms that compose the double zigzag chain structure appearing at high temperatures are locally displaced, resulting in local dimerization. This tendency weakens when Ta is replaced by V or Nb. Our results indicate that the local distortion persistently survives in these ditellurides, where the electronic degrees of freedom, including orbitals, are weakened. We further discuss the origin of local distortion in these ditellurides, which is different from many usual material systems where molecular formation occurs at low temperatures.Comment: 11 pages, 4 figures, 18 tables, To be published in Phys. Rev.

Gradation effects in sediment transport

To determine the effects of grain size and density gradation in oscillatory sheet-flow, experiments are conducted in an oscillating water tunnel. A formal derivation of a schematised transport model shows that the transport rates per sediment fraction can be determined with and without the assumption of an active layer. A technique that measures sediment composition from natural occurring radionuclides is used to determine the transport rates without that assumption of an active layer. The measurements on total sediment transport rates and suspended sediment concentrations show that effects of gradation are present. The effects of size gradation are mainly in the increased transport rates of the coarse fraction with respect to the uniform coarse material and the availability at the bed under similar conditions. The experiments on density graded sediments indicate that total mass-transport rates are larger than the mass-transport rates of quartz material, whilst the transport rates of the quartz fraction show that this fraction is not hindered by the availability at the bed. (C) 2002 Elsevier Science B.V. All rights reserved

Gradation effects in sediment transport

To determine the effects of grain size and density gradation in oscillatory sheet-flow, experiments are conducted in an oscillating water tunnel. A formal derivation of a schematised transport model shows that the transport rates per sediment fraction can be determined with and without the assumption of an active layer. A technique that measures sediment composition from natural occurring radionuclides is used to determine the transport rates without that assumption of an active layer. The measurements on total sediment transport rates and suspended sediment concentrations show that effects of gradation are present. The effects of size gradation are mainly in the increased transport rates of the coarse fraction with respect to the uniform coarse material and the availability at the bed under similar conditions. The experiments on density graded sediments indicate that total mass-transport rates are larger than the mass-transport rates of quartz material, whilst the transport rates of the quartz fraction show that this fraction is not hindered by the availability at the bed. (C) 2002 Elsevier Science B.V. All rights reserved

Thermal Conductivity of the Quantum Spin Liquid Candidate EtMe_{3}Sb[Pd(dmit)_{2}]_{2}: No Evidence of Mobile Gapless Excitations

The thermal conductivity κ of the quasi-2D organic spin-liquid candidate EtMe_{3}Sb[Pd(dmit)_{2}]_{2} (dmit-131) was measured at low temperatures, down to 0.07 K. We observe a vanishingly small residual linear term κ_{0}/T, in κ/T vs T as T→0. This shows that the low-energy excitations responsible for the sizable residual linear term γ in the specific heat C, seen in C/T vs T as T→0, are localized. We conclude that there are no mobile gapless excitations in this spin-liquid candidate, in contrast with a prior study of dmit-131 that reported a large κ_{0}/T value [Yamashita et al., Science 328, 1246 (2010)SCIEAS0036-807510.1126/science.1188200]. Our study shows that dmit-131 is in fact similar to κ-(BEDT-TTF)_{2}Cu_{2}(CN)_{3}, another quasi-2D organic spin-liquid candidate where a vanishingly small κ_{0}/T and a sizable γ are seen. We attribute heat conduction in these organic insulators without magnetic order to phonons undergoing strong spin-phonon scattering, as observed in several other spin-liquid materials