1,136 research outputs found
Tight-binding study of high-pressure phase transitions in titanium: alpha to omega and beyond
We use a tight-binding total energy method, with parameters determined from a
fit to first-principles calculations, to examine the newly discovered gamma
phase of titanium. Our parameters were adjusted to accurately describe the
alpha Ti-omega Ti phase transition, which is misplaced by density functional
calculations. We find a transition from omega Ti to gamma Ti at 102 GPa, in
good agreement with the experimental value of 116 GPa. Our results suggest that
current density functional calculations will not reproduce the omega Ti-gamma
Ti phase transition, but will instead predict a transition from omega Ti to the
bcc beta Ti phase.Comment: 3 encapsulated Postscript figures, submitted to Phyical Review
Letter
Anomalous increase in nematic-isotropic transition temperature in dimer molecules induced by magnetic field
We have determined the nematic-isotropic transition temperature as a function of applied magnetic field in three different thermotropic liquid crystalline dimers. These molecules are comprised of two rigid calamitic moieties joined end to end by flexible spacers with odd numbers of methylene groups. They show an unprecedented magnetic field enhancement of nematic order in that the transition temperature is increased by up to 15K when subjected to 22T magnetic field. The increase is conjectured to be caused by a magnetic field-induced decrease of the average bend angle in the aliphatic spacers connecting the rigid mesogenic units of the dimers
Thermal optical non-linearity of nematic mesophase enhanced by gold nanoparticles – an experimental and numerical investigation
In this work the mechanisms leading to the enhancement of optical nonlinearity of nematic liquid crystalline material through localized heating by doping the liquid crystals (LCs) with gold nanoparticles (GNPs) are investigated. We present some experimental and theoretical results on the effect of voltage and nanoparticle concentration on the nonlinear response of GNP-LC suspensions. The optical nonlinearity of these systems is characterized by diffraction measurements and the second order nonlinear refractive index, n 2 , is used to compare systems with different configurations and operating conditions. A theoretical model based on heat diffusion that takes into account the intensity and finite size of the incident beam, the nanoparticle concentration dependent absorbance of GNP doped LC systems and the presence of bounding substrates is developed and validated. We use the model to discuss the possibilities of further enhancing the optical nonlinearity
Spin Hall effect in Sr2RuO4 and transition metals (Nb,Ta)
We study the intrinsic spin Hall conductivity (SHC) and the -orbital Hall
conductivity (OHC) in metallic -electron systems based on the multiorbital
tight-binding model. The obtained Hall conductivities are much larger than that
in -type semiconductors. The origin of these huge Hall effects is the
"effective Aharonov-Bohm phase" induced by the signs of inter-orbital hopping
integrals as well as atomic spin-orbit interaction. Huge SHC and OHC due to
this mecahnism is ubiquitous in multiorbital transition metals.Comment: 4 pages, 3 figures, Proceedings of SNS conference in Sendai, 200
Robust ab initio calculation of condensed matter: transparent convergence through semicardinal multiresolution analysis
We present the first wavelet-based all-electron density-functional
calculations to include gradient corrections and the first in a solid. Direct
comparison shows this approach to be unique in providing systematic
``transparent'' convergence, convergence with a priori prediction of errors, to
beyond chemical (millihartree) accuracy. The method is ideal for exploration of
materials under novel conditions where there is little experience with how
traditional methods perform and for the development and use of chemically
accurate density functionals, which demand reliable access to such precision.Comment: 4 pages, 3 figures, 4 tables. Submitted to Phys. Rev. Lett. (updated
to include GGA
Second harmonic light scattering induced by defects in the twist-bend nematic phase of liquid crystal dimers
The nematic twist-bend (NTB) phase, exhibited by certain thermotropic liquid crystalline (LC) dimers, represents a new orientationally ordered mesophase -- the first distinct nematic variant discovered in many years. The NTB phase is distinguished by a heliconical winding of the average molecular long axis (director) with a remarkably short (nanoscale) pitch and, in systems of achiral dimers, with an equal probability to form right- and left-handed domains. The NTB structure thus provides another fascinating example of spontaneous chiral symmetry breaking in nature. The order parameter driving the formation of the heliconical state has been theoretically conjectured to be a polarization field, deriving from the bent conformation of the dimers, that rotates helically with the same nanoscale pitch as the director field. It therefore presents a significant challenge for experimental detection. Here we report a second harmonic light scattering (SHLS) study on two achiral, NTB-forming LCs, which is sensitive to the polarization field due to micron-scale distortion of the helical structure associated with naturally-occurring textural defects. These defects are parabolic focal conics of smectic-like ``pseudo-layers", defined by planes of equivalent phase in a coarse-grained description of the NTB state. Our SHLS data are explained by a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a linear coupling between the two
Nematic Twist-Bend Phase with Nanoscale Modulation of Molecular Orientation
Peer reviewedPublisher PD
Probing a non-biaxial behavior of infinitely thin hard platelets
We give a criterion to test a non-biaxial behavior of infinitely thin hard
platelets of symmetry based upon the components of three order
parameter tensors. We investigated the nematic behavior of monodisperse
infinitely thin rectangular hard platelet systems by using the criterion.
Starting with a square platelet system, and we compared it with rectangular
platelet systems of various aspect ratios. For each system, we performed
equilibration runs by using isobaric Monte Carlo simulations. Each system did
not show a biaxial nematic behavior but a uniaxial nematic one, despite of the
shape anisotropy of those platelets. The relationship between effective
diameters by simulations and theoretical effective diameters of the above
systems was also determined.Comment: Submitted to JPS
Rapid decomposition of traditionally produced biochar in an Oxisol under savannah in Northeastern Brazil.
Soil amendment with biochar has been claimed as an option for carbon (C) sequestration in agricultural soils. Most studies on biochar/soil organic carbon (SOC) interactions were executed under laboratory conditions. Here we tested the stability of biochar produced in a traditional kiln and its effects on the stocks of native SOC under field conditions
Structural and superconducting properties of MgBBe
We prepared MgBBe (, 0.2, 0.3, 0.4, and 0.6) samples where
B is substituted with Be. MgB structure is maintained up to .
In-plane and inter-plane lattice constants were found to decrease and increase,
respectively. Superconducting transition temperature decreases with
. We found that the decrease is correlated with in-plane contraction
but is insensitive to carrier doping, which is consistent with other
substitution studies such as MgAlB and MgBC.
Implication of this work is discussed in terms of the 2D nature of -band.Comment: 3 pages,4 figures, to be published in Phys. Rev.
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