Relationship between single-particle excitation and spin excitation at the Mott Transition

An intuitive interpretation of the relationship between the dispersion relation of the single-particle excitation in a metal and that of the spin excitation in a Mott insulator is presented, based on the results for the one- and two-dimensional Hubbard models obtained by using the Bethe ansatz, dynamical density-matrix renormalization group method, and cluster perturbation theory. The dispersion relation of the spin excitation in the Mott insulator is naturally constructed from that of the single-particle excitation in the zero-doping limit in both one- and two-dimensional Hubbard models, which allows us to interpret the doping-induced states as the states that lose charge character toward the Mott transition. The characteristic feature of the Mott transition is contrasted with the feature of a Fermi liquid and that of the transition between a band insulator and a metal.Comment: 6 pages, 2 figures, to appear in JPS Conf. Pro

Several different gas-liquid contactors utilizing centrifugal force

Gas-liquid contactors utilizing centrifugal forc

Mesoscopic conductance fluctuations in a coupled quantum dot system

We study the transport properties of an Aharonov-Bohm ring containing two quantum dots. One of the dots has well-separated resonant levels, while the other is chaotic and is treated by random matrix theory. We find that the conductance through the ring is significantly affected by mesoscopic fluctuations. The Breit-Wigner resonant peak is changed to an antiresonance by increasing the ratio of the level broadening to the mean level spacing of the random dot. The asymmetric Fano form turns into a symmetric one and the resonant peak can be controlled by magnetic flux. The conductance distribution function clearly shows the influence of strong fluctuations.Comment: 4 pages, 4 figures; revised for publicatio

The possible role of stellar mergers for the formation of multiple stellar populations in globular clusters

Many possible scenarios for the formation of multiple stellar populations (MSP) in globular clusters (GCs) have been discussed so far, including the involvement of asymptotic giant branch stars, fast rotating main sequence stars, very massive main sequence stars and mass-transferring massive binaries based on stellar evolution modelling. But self-consistent, dynamical simulations of very young GCs are usually not considered. In this work, we perform direct $N$-body modelling such systems with total masses up to $3.2\times10^5$ M$_\odot$, taking into account the observationally constrained primordial binary properties, and discuss the stellar-mergers driven both by binary stellar evolution and dynamical evolution of GCs. The occurrence of stellar mergers is enhanced significantly in binary-rich clusters such that stars forming from the gas polluted by mergers-driven ejection/winds would appears as MSPs. We thus emphasize that stellar mergers can be an important process that connects MSP formation with star cluster dynamics, and that multiple MSP formation channels can naturally work together. The scenario studied here, also in view of a possible top-heavy IMF, may be particularly relevant for explaining the high mass fraction of MSPs (the mass budget problem) and the absence of MSPs in young and low-mass star clusters

An ab initio study of 3s core-level x-ray photoemission spectra in transition metals

We calculate the $3s$- and $4s$-core-level x-ray photoemission spectroscopy (XPS) spectra in the ferromagnetic and nonmagnetic transition metals by developing an \emph{ab initio} method. We obtain the spectra exhibiting the characteristic shapes as a function of binding energy in good agreement with experimental observations. The spectral shapes are strikingly different between the majority spin channel and the minority spin channel for ferromagnetic metals Ni, Co, and Fe, that is, large intensities appear in the higher binding energy side of the main peak (satellite) in the majority spin channel. Such satellite or shoulder intensities are also obtained for nonmagnetic metals V and Ru. These behaviors are elucidated in terms of the change of the one-electron states induced by the core-hole potential.Comment: 11 pages, 12 figures, to appear in Phys. Rev.

Trans-Magnetosonic Accretion in a Black Hole Magnetosphere

We present the critical conditions for hot trans-fast magnetohydrodynamical (MHD) flows in a stationary and axisymmetric black-hole magnetosphere. To accrete onto the black hole, the MHD flow injected from a plasma source with low velocity must pass through the fast magnetosonic point after passing through the ``inner'' or ``outer'' Alfven point. We find that a trans-fast MHD accretion solution related to the inner Alfven point is invalid when the hydrodynamical effects on the MHD flow dominate at the magnetosonic point, while the other accretion solution related to the outer Alfven point is invalid when the total angular momentum of the MHD flow is seriously large. When both regimes of the accretion solutions are valid in the black hole magnetosphere, we can expect the transition between the two regimes. The variety of these solutions would be important in many highly energetic astrophysical situations.Comment: 27 pages, 12 figures, accepted to Ap

The effect of supersymmetry breaking in the Mass Varying Neutrinos

We discuss the effect of the supersymmetry breaking on the Mass Varying Neutrinos(MaVaNs) scenario. Especially, the effect mediated by the gravitational interaction between the hidden sector and the dark energy sector is studied. A model including a chiral superfield in the dark sector and the right handed neutrino superfield is proposed. Evolutions of the neutrino mass and the equation of state parameter are presented in the model. It is remarked that only the mass of a sterile neutrino is variable in the case of the vanishing mixing between the left-handed and a sterile neutrino on cosmological time scale. The finite mixing makes the mass of the left-handed neutrino variable.Comment: 6 pages, 7 figures, RevTeX4, references added, discussions and figures revise

Biquadratic antisymmetric exchange and the magnetic phase diagram of magnetoelectric CuFeO2_2

Biquadratic {\it antisymmetric} exchange terms of the form $- [C_{ij} e^{\alpha}_{ij}({\bf s}_i\times{\bf s}_j)_z]^2$, where ${\bf e}_{ij}$ is the unit vector connecting sites $i$ and $j$ and $\alpha = x,y$, due partially to magnetoelectric coupling effects, are shown to be responsible for the spin-flop helical phase in CuFeO$_2$ at low magnetic field and temperature. Usual biquadratic {\it symmetric} exchange, likely due to magnetoelastic coupling, is found to support the stability of axial magnetic states at higher fields in this nearly-Heisenberg like stacked triangular antiferromagnet. A model Hamiltonian which also includes substantial interplane and higher-neighbor intraplane exchange interactions, reproduces the unique series of observed commensurate and incommensurate periodicity phases with increasing applied magnetic field in this highly frustrated system. The magnetic field-temperature phase diagram is discussed in terms of a Landau-type free energy.Comment: 7 pages, 9 figure

Theory of resonant inelastic x-ray scattering at the K edge in La2_2CuO4_4 - Multiple scattering effects -

We develop a theory of resonant inelastic x-ray scattering (RIXS) at the $K$ edge in La$_2$CuO$_4$ on the basis of the Keldysh Green's function formalism. In our previous analysis (Phys. Rev. B 71, 035110 (2005)), the scattering by the core-hole potential was treated within the Born approximation, and a crude-model density of states was used for the $4p$ band. We improve the analysis by taking account of the multiple scattering in Cu3d-O$2p$ bands and by using a realistic $4p$ DOS obtained from a band calculation. The multiple scattering effect is evaluated with the use of the time representation developed by Nozi\`eres and De Dominicis. It is found that the multiple scattering effect makes the $K$-edge peak in the absorption coefficient shift to the lower energy region as a function of photon energy, that is, the photon energy required to excite the $1s$ electron to the $K$-edge peak reduces. It is also found that the multiple-scattering effect does not change the two-peak structure in the RIXS spectra but modifies slightly the shape as a function of energy loss. These findings suggests that the multiple scattering effect could mainly be included into a renormalization of the core-level energy and partly justify the Born approximation, leading to a future application to the RIXS in three-dimensional systems.Comment: revised version with extended discussion, 24 pages, 12 figures, accepted for PR