1,915 research outputs found
Superconductivity from a long-range interaction: a crossover between the electron gas and the lattice model
We explore how the superconductivity arising from the on-site
electron-electron repulsion will change when the repulsion is changed to a
long-ranged, 1/r-like one by introducing an extended Hubbard model with the
repulsion extending to distant (12th) neighbors. With a simplified
fluctuation-exchange approximation, we have found for the square lattice that
(i) as the band filling becomes dilute enough, the charge susceptibility
becomes comparable with the spin susceptibility, where p and then s pairings
become dominant, in agreement with the result for the electron gas by Takada,
while (ii) the d-wave, which reflects the lattice structure, dominates well
away from the half filling. All these can be understood in terms of the spin
and charge structures along with the shape and size of the Fermi surface.Comment: 5 pages, 6 figure
Mechanisms of enhanced orbital dia- and paramagnetism: Application to the Rashba semiconductor BiTeI
We study the magnetic susceptibility of a layered semiconductor BiTeI with
giant Rashba spin splitting both theoretically and experimentally to explore
its orbital magnetism. Apart from the core contributions, a large
temperature-dependent diamagnetic susceptibility is observed when the Fermi
energy E_F is near the crossing point of the conduction bands, while the
susceptibility turns to be paramagnetic when E_F is away from it. These
features are consistent with first-principles calculations, which also predict
an enhanced orbital magnetic susceptibility with both positive and negative
signs as a function of E_F due to band (anti)crossings. Based on these
observations, we propose two mechanisms for an enhanced paramagnetic orbital
susceptibility.Comment: 4 figures; added reference
Multipole expansion for magnetic structures: A generation scheme for symmetry-adapted orthonormal basis set in crystallographic point group
We propose a systematic method to generate a complete orthonormal basis set
of multipole expansion for magnetic structures in arbitrary crystal structure.
The key idea is the introduction of a virtual atomic cluster of a target
crystal, on which we can clearly define the magnetic configurations
corresponding to symmetry-adapted multipole moments. The magnetic
configurations are then mapped onto the crystal so as to preserve the magnetic
point group of the multipole moments, leading to the magnetic structures
classified according to the irreducible representations of crystallographic
point group. We apply the present scheme to pyrhochlore and hexagonal ABO3
crystal structures, and demonstrate that the multipole expansion is useful to
investigate the macroscopic responses of antiferromagnets
Density-matrix renormalization group study of pairing when electron-electron and electron-phonon interactions coexist: effect of the electronic band structure
Density-matrix renormalization group is used to study the pairing when both
of electron-electron and electron-phonon interactions are strong in the
Holstein-Hubbard model at half-filling in a region intermediate between the
adiabatic (Migdal's) and antiadiabatic limits. We have found: (i) the pairing
correlation obtained for a one-dimensional system is nearly degenerate with the
CDW correlation in a region where the phonon-induced attraction is comparable
with the electron-electron repulsion, but (ii) pairing becomes dominant when we
destroy the electron-hole symmetry in a trestle lattice. This provides an
instance in which pairing can arise, in a lattice-structure dependent manner,
from coexisting electron-electron and electron-phonon interactions.Comment: 4 pages, 3 figures; to appear in Phys. Rev. Let
Enhanced entrainability of genetic oscillators by period mismatch
Biological oscillators coordinate individual cellular components so that they
function coherently and collectively. They are typically composed of multiple
feedback loops, and period mismatch is unavoidable in biological
implementations. We investigated the advantageous effect of this period
mismatch in terms of a synchronization response to external stimuli.
Specifically, we considered two fundamental models of genetic circuits: smooth-
and relaxation oscillators. Using phase reduction and Floquet multipliers, we
numerically analyzed their entrainability under different coupling strengths
and period ratios. We found that a period mismatch induces better entrainment
in both types of oscillator; the enhancement occurs in the vicinity of the
bifurcation on their limit cycles. In the smooth oscillator, the optimal period
ratio for the enhancement coincides with the experimentally observed ratio,
which suggests biological exploitation of the period mismatch. Although the
origin of multiple feedback loops is often explained as a passive mechanism to
ensure robustness against perturbation, we study the active benefits of the
period mismatch, which include increasing the efficiency of the genetic
oscillators. Our findings show a qualitatively different perspective for both
the inherent advantages of multiple loops and their essentiality.Comment: 28 pages, 13 figure
Application of the Spiritual Intelligence Self-Report Inventory (SISRI-24) Among Hong Kong University Students
The aim of this study was to examine the psychometric properties of the Chinese version of the Spiritual Intelligence Self-Report Inventory (SISRI-24). Two hundred thirteen undergraduate students in Hong Kong completed the Chinese SISRI-24, the Meaning of Life Questionnaire, the Metapersonal Self-Construal Scale, and the Satisfaction with Life Scale to allow examination of internal reliability and construct validity. Confirmatory factor analysis was also performed to examine whether the model of King and DeCicco (2009) fit our data. Our results indicated that the full scale of the Chinese SISRI-24 and its four subscales had acceptable internal reliability. The results also showed a positive relationship between spiritual intelligence and metapersonal self-construal. However, no significant relationship was reported between spiritual intelligence and life satisfaction. As such, construct validity was low to moderate. This study can be considered a foundation for understanding and measuring spiritual intelligence among undergraduate students in Hong Kong. Future research directions are suggested
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