Time-domain interferometry experiments using multi-line nuclear absorbers

Langmuir-Blodgett (LB) films of octadecanoyl hydroxamic acid (C18N) complexed with Fe^3?+? ions have been prepared at various subphase pH values. The LB films consisting of different number of layers were investigated by ⁵⁷Fe conversion electron M?ssbauer spectroscopy (CEM) at room temperature. The CEM detector contained a piece of α-iron, enriched with ⁵⁷Fe, using as an internal standard. The M?ssbauer pattern of the C18N/Fe LB films is a doublet with parameters δ = 0.35?mm/s and Δ = 0.74?mm/s. A gradual increase of the relative occurrence of the doublet compared to the sextet of the internal standard was observed with the increasing number of layers, indicating the nearly uniform distribution of Fe among the LB layers.     

A basis for S k (Γ 0(4)) and representations of integers as sums of squares

In this paper, we find a basis for the space S _k (?? ₀(4)) of cusp forms of even weight k for the congruence subgroup ?? ₀(4) in terms of Eisenstein series. As an application, we obtain formulas for r _4s (n), the number of ways to represent a nonnegative integer n as a sum of 4s integral squares.     

Circularly polarized lasing over wide wavelength range in spin-controlled (1 1 0) vertical-cavity surface-emitting laser

We investigated the emission wavelength dependence of the lasing polarization in a (1 1 0)-oriented vertical-cavity surface-emitting laser (VCSEL) with GaAs/AlGaAs quantum wells under optical spin injection at room temperature. Lasing was observed in the one circularly polarized mode over a wide wavelength range from 838 to 857 nm, in which a degree of circular polarization higher than 0.8 was maintained. The optical gain spectrum that contributed to the circularly polarized lasing is discussed based on the optical selection rules and the measured polarization-resolved photoluminescence spectra of the active layers.     

Dependence of the Schottky barrier on the work function at metal/SiON/SiC(0001) interfaces identified by first-principles calculations

We report investigations based on density functional theory that clarify the dependence of the Schottky barrier height (SBH) on the work function of metals at metal/SiON interfaces formed on the 6H-SiC(0001) surface. We have found that the density of atoms in the Al layer affects neither its work function nor the SBH formed when the layer contacts with the SiON surface. More importantly, the SBH for the B overlayer is lower compared with that for the Al layer, reflecting a difference in the work function of the layers. The present result clearly indicates that Fermi-level pinning does not occur for SiON on SiC(0001), which means that the SBH is controllable for metal/SiON/SiC systems by changing the work function of metals.     

Curie temperatures of CoPt ultrathin continuous films

The effects of layer thickness and thermal annealing on Curie temperature have been studied for CoPt ultrathin continuous layers in AlN/CoPt multilayer structures. It is found that there exists a critical thickness below which Curie temperature rapidly decreases due to the loss of spin-spin interactions in the vicinity of interface. After high temperature annealing, the in-plane lattice constant of CoPt film is increased and the exchange coupling parameter is decreased. Consequently, Curie temperatures decrease for some films with large thickness, compared with as-deposited state. Upon annealing at 600?^°C, CoPt undergoes ordering transformation, which also contributes to the degradation of the Curie temperature. However, when the CoPt film thickness is below 2?nm, the Curie temperature is increased after annealing. Especially for 1?nm thick film, the Curie temperature is strikingly increased from 173?^°C to 343?^°C after annealing at 600?^°C. This effect is attributed to the out-of-plane lattice deformation of CoPt thin layers in AlN/CoPt multilayer structures.     

Generation of a decoherence-free entangled state using a radio-frequency dressed state

We propose the generation of entangled states with trapped calcium ions using a combination of an rf dressed state and a spin-dependent force. By using this method, a decoherence-free entangled state of rf qubits can be directly generated, and ideally its fidelity is close to unity. We demonstrate an rf entangled state with a fidelity of 0.68±0.08, which has a coherence time of more than 200 ms by virtue of the fact that it is an eigenstate with energy gaps between adjacent levels. Using the same technique, we also produce a qutrit-qutrit entangled state with a fidelity of 0.77±0.09, which exceeds the threshold value for separability of 2/3.     

Formation of biomimetic hierarchical nanostructure in homopolymers and block copolymer ternary blend particles

In order to mimic hierarchical nanostructures in nature,particles of polymer blends consisting of poly(4-butyltriphenylamine) (PBTPA),poly(methyl methacrylate) ...     

Challenge of ultra high frequency limit of permeability for magnetic nanoparticle assembly with organic polymer—Application of superparamagnetism

Permeability and its upper limitation frequency of superparamagnetic nanoparticle type magneto-dielectric hybrid material were theoretically and experimentally investigated. The Landau-Lifschitz-Gilbert equation without any interaction between nanoparticles revealed that the blocking resonance frequency was able to exceed the ferromagnetic resonance frequency originating from the intrinsic magnetocrystalline anisotropy field by decreasing particle size, resulting in ultra fast switching of superparamagnetic moment in GHz range. In the case of Fe nanoparticles, the blocking resonance frequency can be increased to 130 GHz by reducing particle size to 1 nm. The experiment results for Fe₃O₄ and Fe nanoparticle assemblies supported the validity of our calculation results. Thus, superparamagnetic nanoparticle assembly could be promising material for high frequency use over 10 GHz range.     

Phase diagram of electron-hole systems: Interplay between exciton Mott transition and quantum pair condensation

Quasi-thermal-equilibrium states of electron-hole (e-h) systems in photoexcited insulators are studied from a theoretical viewpoint, stressing the exciton Bose-Einstein condensation (BEC), the e-h BCS-type pair-condensed state, and the exciton Mott transition between an insulating exciton/biexciton gas phase and a metallic e-h plasma phase. We determine the quasi-equilibrium phase diagram of the e-h system at zero and finite temperatures with applying the dynamical mean-field theory (DMFT) to the e-h Hubbard model with both repulsive and attractive on-site interactions. Effects of inter-site interactions on the exciton Mott transition are also clarified with applying the extended DMFT to the extended e-h Hubbard model.     

Highly enantioselective Diels–Alder reaction of Danishefsky-type diene and electron-deficient olefins catalyzed by an Yb(III)/chiral bis-urea complex

The synthesis and utility of the novel axially chiral bis-urea ligand BINUREA are described. A complex of this urea ligand with ytterbium triflate and DBU can be used in the catalytic enantioselective Diels–Alder reaction of Danishefsky-type diene and electron-deficient olefins to give the adducts in good to excellent yield and enantiomeric excess (ee).