Search

We study a local antisymmetric spin-orbit (ASO) coupling effect on a triangular-triple-quantum-dot (TTQD) system as a theoretical proposal for a new application of the Kondo physics to nanoscale devices. The electric polarization induced by the Kondo effect is strongly correlated with the spin configurations and molecular orbital degrees of freedom in the TTQD. In particular, an abrupt sign reversal of the emergent electric polarization is associated with a quantum critical point in a magnetic field, which can also be controlled by the ASO coupling that changes the mixing weight of different orbital components in the TTQD ground state.

We designed a reflectometer for grazing-incidence X-ray measurements with a rotational feedthrough consisting of three welded bellows and a circle-type goniometer. This apparatus does not require differential pumping and is suitable for ultra-high-vacuum applications. With this reflectometer, we successfully performed high-precision synchrotron radiation X-ray reflectivity measurements on a thin iron-film under an ultra-high-vacuum condition.

A micro-beam NRA system, by means of a resonant nuclear reaction 1H(15N, αγ)12C, has been developed for the purpose of the 3D mapping of the hydrogen distribution in solids. To obtain the tens μm size of the beam spot, the combination of the newly proposed tapered glass capillary and a conventional quadrupole magnetic lens is employed. An Y patterned film on a substrate is prepared as an application of the developed system. The 6 MeV 15N beam focused by glass capillaries down to 50 μm successfully shows the hydrogen distribution. The in-plane NRA profile implies that the beam emitted from the glass capillary outlet is parallel, although the original beam has a considerable divergence. The NRA measurements in the 103 Pa N2 atmosphere due to the low gas conductance of the glass capillary is also demonstrated.

Hydrogen adsorbed on the Pt(1 1 1)–Sn surface alloys was investigated by nuclear reaction analysis (NRA) using 1H(15N,αγ)12C. The γ-ray intensity profile as a function of the incident ion energy is analyzed on the basis of the Doppler broadening. From the widths of the resonance profiles, the zero-point vibrational energies in the vertical and in-plane directions are estimated to be 78.2 ± 3.7 and 53.6 ± 5.8 meV on Pt(1 1 1)2 × 2–Sn, respectively, and 72.5 ± 3.7 and 58.5 ± 6.7 meV on Pt(1 1 1)√3 × √3–Sn, respectively. The adsorption state and vibrational property of H on the surface alloys are discussed.

Ultra-thin films of Cr2O3(0 0 0 1) grown on Cr(1 1 0) were investigated by reflection absorption infrared spectroscopy (RAIRS). An absorption band at 720 cm−1 is assigned to a longitudinal optical phonon of Cr2O3. With increasing O2 exposure, this absorption band shifts to higher frequency, which is qualitatively explained by a simple spring model. After successive oxidation with 18O2 and 16O2, two absorption bands corresponding to Cr 2 18 O 3 and Cr 2 16 O 3 were distinctly observed suggesting that oxygen diffusion hardly occurs during the oxide growth. Temperature dependence of the RAIRS spectrum taken from the Cr2O3 film revealed that the absorption band position shifts to lower frequency along with broadening of the band width. Anharmonic coupling with low-frequency phonons and effects of the antiferromagnetic to paramagnetic phase transition are discussed.

We measured the flux flow resistivity ρ f associated with a purely viscous motion of the vortices in high-quality MgB 2 by the microwave surface impedance. The flux flow resistivity exhibits unusual field dependence with strong enhancement at low fields, which is markedly different from that in conventional s-wave superconductors. A crossover field which separates two distinct flux flow regime with different slope of ρ f was observed in H ∥ ab -plane. The unusual H -dependence indicates that two very differently sized superconducting gaps in MgB 2 manifest themselves clearly in the vortex dynamics and nearly equally contribute to the energy dissipation.

We report experimental results on the interaction of hydrogen with monolayer thin Ag and Au films grown on a Pt(1 1 1) substrate, measured with thermal desorption spectroscopy (TDS) and nuclear reaction analysis (NRA). We found that H2 dissociative adsorption is activated on both thin film surfaces. Atomic hydrogen was found to adsorb on the Ag and Au films on Pt(1 1 1) with main desorption temperatures of 160 and 120 K, respectively. The monolayer thin Ag and Au films on Pt(1 1 1) are chemically similar to the (1 1 1) surfaces of bulk Ag and Au, respectively.

The adsorption structure of NO on the Pt(1 1 1) surface at low temperature (90–130 K) was studied by dynamical analysis of low-energy electron diffraction and reflection absorption infrared spectroscopy. Three different 2×2 patterns were identified and their experimental intensity vs. voltage curves ( I – V curves) were compared with dynamically calculated I – V curves for the models including the tilted (bent) NO geometry. The differences of I – V curves can be recognized by virtue of the wider incident electron energy range than the previous dynamical analysis. The most promising interpretation is that NO occupies three sites sequentially depending on the NO coverage. In this interpretation, NO first adsorbs at the threefold fcc hollow site, next at the atop site and last at the threefold hcp hollow site. The NO saturation coverage is 0.75 ML ( 1 ML =1.5×10 −15 molecules/cm 2 ). The NO species at the atop site is tilted and those at both hollow sites are upright. Our new model agrees well with the recent density functional theory calculation and explains the experimental results better than the previous model, in which NO transits from the bridge site to the atop site with increasing coverage.

The adsorption and photoreaction of NO on Ag films deposited on Pt(1 1 1) were investigated at 90 K by reflection-absorption infrared spectroscopy (RAIRS). Similar to Ag(1 1 1), NO molecules were found to be converted into (NO) 2 and N 2 O on the Ag films. At an Ag thickness of 1 ML, however, a new adsorption state that reveals a RAIRS band at 1848 cm −1 is present on the surface. The (NO) 2 dimer species was found to react into N 2 O, while the reaction of the new species was substantially suppressed. Upon photon irradiation with a wavelength of 193 nm, the three adsorption species on Ag(1 ML)/Pt(1 1 1) were depleted from the surface. The origin of the newly found species and the photoreaction mechanism are discussed.

The adsorption and initial absorption of hydrogen (H2) by Pd(1 0 0) at T=100–160 K are investigated by thermal desorption spectroscopy (TDS) and nuclear reaction analysis, which enables a depth-resolved determination of the hydrogen concentration at and below the Pd surface. Under 3×10−8 mbar H2 and T 130 K H-migration from such a near-surface hydride phase to the deeper bulk of the metal occurs and a solution of H in Pd is formed by means of facile diffusion. This bulk dissolved hydrogen emerges as a broad structure in TDS at T=200–260 K exhibiting a tailing at high temperatures characteristic of diffusion-controlled desorption kinetics.

We investigate exciton-mediated triplet superconductivity in a T h system PrOs4Sb12 and discuss a twofold symmetry of the gap function corresponding to the lower magnetic field phase.

Cu 3 ( CO 3 ) 2 ( OH ) 2 is a new compound consisting of diamond shaped spin chains. Magnetization measurements revealed a plateau at 1 3 of the saturated moment. This feature together with the magnetic excitations observed by high-field electron spin resonance (ESR) measurements can be understood as a model of coupled spin dimer and monomer system. We present a theory for the magnetic excitations of this system based on an extended bond-operator theory, and discuss the field dependence of the observed excitation modes by the ESR measurements.

The magnon dispersion in the field-induced and pressure-induced antiferromagnetically (AF) ordered phase in TlCuCl 3 are studied. In the pressure-induced AF phase, there are two transverse phase (Goldstone) modes and one gapped longitudinal amplitude mode. A magnetic field lifts the degeneracy, and it gives rise to three separated magnon branches in the field-induced AF phase, where the lowest lying mode corresponds to a Goldstone mode. A model consisting of three distinct dimer sublattices is proposed to account for the plateaus which appear in magnetization curves of NH 4 CuCl 3 .

The local density of states of quasi-particles, N(E,r), around columnar defects generated by bombardment of high-energy heavy ions parallel to the c-axis in Bi2Sr2CaCu2Ox (Bi-2212) and 2H-NbSe2 has been studied by scannning tunneling spectroscopy at 4.2 K and compared. The regions of columnar defects have been found to be insulating and circular superconductor–insulator boundaries have been studied. In Bi-2212 the N(E,r) has exhibited the increase at E=0 meV and the decrease at E∼35 meV at [1 1 0] and [ 1 1 0] directions in CuO2 square network and seems to show the pattern with four-fold symmetry, while in 2H -NbSe2 such things have not been observed. This is new evidence of the presence of dx2–y2 component in the order parameter of Bi-2212.

The chiral optical absorption by a single vortex in a p_x \pm i p_y-wave superconductor is studied theoretically. The p_x \pm i p_y-wave state was recently suggested as the symmetry of the order parameter of Sr_2 Ru O_4 superconductor. Due to the violation of time reversal symmetry, there are two types of vortices whose winding orientation is the same or opposite to the angular momentum of the Cooper pair. In a real material domains with p_x \pm i p_y-wave states are expected. However, optical absorption of circular polarized light depends only on the winding of the vortex and has a low energy absorption peak which results in dichroism. Dichroism occurs if superconductivity is realized on a single Fermi surface sheet. However, in the case of several Fermi surface sheets dichroism may disappear, if the both types of carriers are present, electron-like and hole-like. Therefore chiral optical absorption is a possible experiment to detect the orbital dependent superconductivity which was suggested as the superconducting state of Sr_2 Ru O_4.

The microscopic mechanism of circular currents induced in the vicinity of a non-magnetic impurity is analyzed for the (time-reversal symmetry breaking) chiral superconducting state d ( k )= z (k x ± i k y ) which is very likely realized in Sr2RuO4. From the analytic, not self-consistent solution of the Bogolyubov–de Gennes equations we find two types of quasiparticle states, a bound state and the continuum state. Through impurity scattering the condensate transfers angular momentum to the quasiparticle states which generate a circular current.