Bohmian trajectories for photons

The first examples of Bohmian trajectories for photons have been worked out for simple situations, using the Kemmer–Duffin–Harish-Chandra formalism.     

Infra red quantum dot photolithography

CdS quantum dots were fabricated photolithographically on the surface and in the bulk of silica hydrogels, as well as on the surface of planar substrates. Silica hydrogels were prepared with a standard base-catalyzed route, and the solvent was exchanged with a cold aqueous solution of Cd(NO₃)₂, NH₄OH, thiourea, and a capping agent, e.g., 2-mercaptoethanol. The samples were then exposed to a focused infrared beam produced by a continuous-wave Nd:YAG laser. The precursors reacted upon heating, and CdS nanoparticles formed in the illuminated regions. Use of capping agents allowed to control the mean particle size, while focusing of the beam inside hydrogel monoliths generated nanoparticles in their bulk, but not at the surface. Planar substrates were patterned by illuminating a precursor solution spin-coated on the substrates. The average size of the CdS nanoparticles could be varied between about 1.5 and 4.5 nm by varying the type and the concentration of the capping agents.     

3-[4-Bromo-α(<Emphasis Type="Italic">R</Emphasis>*)-methoxybenzyl]-6-chloro-3(<Emphasis Type="Italic">S</Emphasis>*),4(<Emphasis Type="Italic">S</Emphasis>*)-dihydroxychroman: X-ray and DFT Studies

Sodium borohydride reduction of E-3-benzylidenechromanone epoxides in dry methanol has afforded 3(S*), 4(S*)-dihydroxy-3-[α(R*)-methoxybenzyl]chromans as an interesting class of products, the structures of which have been assigned mainly from spectral data and consideration of the mechanistic aspects. X-ray diffraction study of one of them, 3-[4-bromo-α(R*)-methoxybenzyl]-6-chloro-3(S*),4(S*)- dihydroxychroman, is performed. The title compound crystallizes in the monoclinic sp. gr. P2₁/n, with a = 13.336(6) Å, b = 10.866(5) Å, c = 27.166(11) Å, β = 95.193(6)°, V = 3920(3) ų, and Z = 8. Supramolecular construction of the compound involves O–H···O intermolecular hydrogen bonds as well as three other types of non-covalent interactions which are responsible for crystal packing. Density functional theory was applied for geometry optimization, molecular orbital calculations, and prediction of UV spectral features. The geometric parameters (bond lengths, bond angles, and dihedral angles) for the representative compound obtained from density functional theory with B3LY6-31G basis set were in good agreement with experimental values.     

Metallic nonsuperconducting phase and D-wave superconductivity in Zn-substituted La1.85Sr0.15CuO4

Measurements of the resistivity, magnetoresistance, and penetration depth were made on films of La1.85Sr0.15CuO4, with up to 12 at. % of Zn substituted for the Cu. The results show that the quadratic temperature dependence of the inverse square of the penetration depth, indicative of d-wave superconductivity, is not affected by doping. The suppression of superconductivity leads to a metallic nonsuperconducting phase, as expected for a pairing mechanism related to spin fluctuations. The metal-insulator transition occurs in the vicinity of k(F)l approximately 1, and appears to be disorder driven, with the carrier concentration unaffected by doping.     

The large N limit of the O(N) Heisenberg spin system in two dimensions

The large N limit of the O(N) Heisenberg spin system in two dimensions (a lattice version of the non-linear σ-model) is analysed by the collective field technique. A compact expression for the mass gap and the β-function is obtained for arbitrary but fixed gN. The strong and weak coupling limits of this expression correctly reproduce the known results.     

Propagation of high power helicons in n-indium antimonide crystal

The propagation of high power helicon in n-InSb has been analysed taking into account the heating of the carriers by the electric field of the wave. The momentum and energy transfer of the electrons have been taken to be due to acoustic phonons and polar optical phonons scattering at 77°K respectively. The sample is assumed to be finite and the wave is incident on the semiconductor-free space interface. Calculations have been made for phase constant, attenuation constant, reflection coefficient and the electron temperature as function of the magnetic field and the wave amplitude. The theoretical results are found to be in qualitative agreement with the experimental observations of Laurinavichyus and Pozhela[14].     

Parametric excitation of acoustohelicon waves in a piezoelectric semiconductor

The parametric excitation of acoustohelicon waves has been studied in a piezoelectric semiconductor in the presence of a strong high frequency oscillatory electric field. The threshold electric field amplitude and the growth rate of the unstable mode have been obtained analytically and for n-InSb at 77 K the unstable mode is found to be propagating with a growth rate ～10³ s^?1 when the crystal is irradiated with a 10.6 μm CO₂ laser.     

Thermal conductivity of geometrically frustrated, ferroelectric YMnO3: extraordinary spin-phonon interactions

The thermal conductivity of the magnetically frustrated, ferroelectric YMnO3 exhibits an isotropic suppression in the cooperative paramagnetic state, followed by a sudden increase upon magnetic ordering. This unprecedented behavior without an associated static structural distortion probably originates from the strong dynamic coupling between acoustic phonons and low-energy spin fluctuations in geometrically frustrated magnets. The replacement of magnetic Ho for Y at the ferroelectrically active site results in an even larger effect, suggestive of the strong influence of multiferroicity.