Superconducting pi qubit with a ferromagnetic Josephson junction

Solid-state qubits have the potential for the large-scale integration and for the flexibility of layout for quantum computing. However, their short decoherence time due to the coupling to the environment remains an important problem to be overcome. We propose a new superconducting qubit which incorporates a spin-electronic device: the qubit consists of a superconducting ring with a ferromagnetic pi junction which has a metallic contact and a normal Josephson junction with an insulating barrier. Thus, a quantum coherent two-level state is formed without an external magnetic field. This feature and the simple structure of the qubit make it possible to reduce its size leading to a long decoherence time.     

Low energy electronic states and triplet pairing in layered cobaltate

The structure of the low-energy electronic states in layered cobaltates is considered starting from the Mott insulating limit. We argue that the coherent part of the wave functions and the Fermi-surface topology at low doping are strongly influenced by spin-orbit coupling of the correlated electrons on the t(2g) level. An effective t-J model based on mixed spin-orbital states is radically different from that for the cuprates, and supports unconventional, pseudospin-triplet pairing.     

Temperature dependence of the electronic structure of Sr14Cu24O41 studied by resonant inelastic X-ray scattering

We report a resonant inelastic X-ray scattering (RIXS) study of charge excitations in the two-leg ladder Sr₁₄Cu₂₄O₄₁. RIXS spectra at 1–5 eV are found to be dependent on temperature. An intraband excitation of the ladder, which appears as a continuum intensity below the Mott gap, decreases in intensity with temperature. Because the intraband excitation is related to the dynamics of doped holes in the ladder, its decrease of the intraband excitation is attributed to the reduction of the mobile holes in the ladder at low temperature.     

Effects of mechanical rotation on spin currents

We study the Pauli-Schr?dinger equation in a uniformly rotating frame of reference to describe a coupling of spins and mechanical rotations. The explicit form of the spin-orbit interaction (SOI) with the inertial effects due to the mechanical rotation is presented. We derive equations of motion for a wave packet of electrons in two-dimensional planes subject to the SOI. The solution is a superposition of two cyclotron motions with different frequencies and a circular spin current is created by the mechanical rotation. The magnitude of the spin current is linearly proportional to the lower cyclotron frequency.     

Unusually small electrical resistance of three-dimensional nanoporous gold in external magnetic fields

We report the electric conductivity of three-dimensional (3D) nanoporous gold at low temperatures and in strong magnetic fields. It was found that topologically disordered 3D nanoporosity leads to extremely low magnetoresistance and anomalous temperature dependence as the characteristic length of nanoporous gold is tuned to be approximately 14 nm. This study underscores the importance of 3D topology of a nanostructure on electronic transport properties and has implications in manipulating electron transport by tailoring 3D nanostructures.     

Permeability control of metal ions using temperature- and pH-sensitive gel membranes

Temperature- and pH-sensitive copolymer gels were synthesized by the simultaneously occurring radiation-induced polymerization and self-bridging of acryloyl- -proline methyl ester (A-ProOMe) with acrylic acid (AAc) in aqueous solutions. The gel swelling behavior and the metal permeation characteristic of its gel membrane were investigated with regard to very slight changes of temperature and pH. The pH threshold of the swelling of a copoly(A-ProOMe/AAc, 70/30 mol%) gel in the range of 5–30°C lay in the region between pH 4.0 and 5.0. The permeability results of metal ions showed that at 40°C the gel membrane blocks the permeation of lithium (Li) and cesium (Cs) ions at pH values lower than 4.75 and 4.60, respectively. The permselectivity (P_Li/Cs value) of the two metal ions at 30°C was also studied and, as a result, its value was obtained to be 1.33 at pH 4.65 and 30°C. This permeation study indicates that the selective metal separation of copoly(A-ProOMe/AAc) gel membranes can be controlled by changing temperature and pH values.     

Regioselective synthesis of bis(silyl enol ethers) and bis(conjugated enones) through electron transfer from Mg metal

Treatment of α,β-unsaturated ketones with Mg metal in the presence of trimethylsilyl choride (TMSCl) brought about facile and regioselective reductive dimerization to give the corresponding bis(silyl enol ethers), 1,6-bis(trimethylsilyloxy)-1,5-dienes. Similar Mg-promoted reductive dimerization of 1,3-cyclic diketones in the presence of TMSCl followed by acid-catalyzed hydrolysis led to selective formation of the corresponding 1,6-diketo-2,4-dienes in moderate to good yields.     

Exchange interaction in covalently bonded biradical-monoradical composite molecules

As a novel molecular designing for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of "single-component ferrimagnetics". When a pi-biradical with an S = 1 ground state and a pi-monoradical with S = (1)/(2) are united by sigma-bonds, the pi-conjugation between the biradical and the monoradical moieties should be truncated in the resultant triradical. This gives magnetic degrees of freedom for both S = 1 and (1)/(2) in the single molecule, serving as a building block for organic molecule-based ferrimagnets under favorable conditions (single-component ferrimagnetics). We have designed and synthesized a triradical, 3-(1'-oxyl-3'-oxido-4',4',5',5'-tetramethylimidazolin-2-yl)benzoic acid 2,4-bis(1' '-oxyl-3' '-oxido-4' ',4' ',5' ',5' '-tetramethylimidazolin-2-yl)phenyl ester (4), as a model compound for the novel approach to genuinely organic ferrimagnets. In the triradical 4, a m-phenylene-bis(nitronyl nitroxide) biradical with a triplet (S = 1) ground state is united with a phenyl nitronyl nitroxide monoradical (S = (1)/(2)) by an ester coupler. Solution-phase ESR spectra from 4 exhibited a complex hyperfine splitting due to (14)N and (1)H nuclei. The analysis of the hyperfine structure based on perturbation calculations has revealed that the exchange interaction within the biradical moiety is much larger than those between the biradical and the monoradical moieties and the magnetic degrees of freedom for both S = 1 and (1)/(2) are retained in 4. An X-ray crystal structure analysis showed that the triradical molecules are arranged in a one-dimensional molecular chain in the crystal. The magnetic susceptibility in a crystalline solid state is consistent with the crystal structure.