1,301 research outputs found
Spectrum of Proton-Induced Mutagenesis of Escherichia coli crp Gene.
開始ページ、終了ページ: 冊子体のページ付
Spin Fluctuation Induced Superconductivity Controlled by Orbital Fluctuation
A microscopic Hamiltonian reflecting the correct symmetry of -orbitals is
proposed to discuss superconductivity in heavy fermion systems. In the
orbitally degenerate region in which not only spin fluctuations but also
orbital fluctuations develop considerably, cancellation between spin and
orbital fluctuations destabilizes -wave superconductivity.
Entering the non-degenerate region by increasing the crystalline electric
field, -wave superconductivity mediated by antiferromagnetic
spin fluctuations emerges out of the suppression of orbital fluctuations. We
argue that the present scenario can be applied to recently discovered
superconductors CeTIn (T=Ir, Rh, and Co).Comment: 4 pages, 3 figure
Electronic states and pairing symmetry in the two-dimensional 16 band d-p model for iron-based superconductor
The electronic states of the FeAs plane in iron-based superconductors are
investigated on the basis of the two-dimensional 16-band d-p model, where the
tight-binding parameters are determined so as to fit the band structure
obtained by the density functional calculation for LaFeAsO. The model includes
the Coulomb interaction on a Fe site: the intra- and inter-orbital direct terms
U and U', the exchange coupling J and the pair-transfer J'. Within the random
phase approximation (RPA), we discuss the pairing symmetry of possible
superconducting states including s-wave and d-wave pairing on the U'-J plane.Comment: 2 pages, 4 figures; Proceedings of the Int. Symposium on
Fe-Oxipnictide Superconductors (Tokyo, 28-29th June 2008
Strong-coupling theory of superconductivity in a degenerate Hubbard model
In order to discuss superconductivity in orbital degenerate systems, a
microscopic Hamiltonian is introduced. Based on the degenerate model, a
strong-coupling theory of superconductivity is developed within the fluctuation
exchange (FLEX) approximation where spin and orbital fluctuations, spectra of
electron, and superconducting gap function are self-consistently determined.
Applying the FLEX approximation to the orbital degenerate model, it is shown
that the -wave superconducting phase is induced by increasing the
orbital splitting energy which leads to the development and suppression of the
spin and orbital fluctuations, respectively. It is proposed that the orbital
splitting energy is a controlling parameter changing from the paramagnetic to
the antiferromagnetic phase with the -wave superconducting phase
in between.Comment: 4 figures, submitted to PR
Multipole correlations in low-dimensional f-electron systems
By using a density matrix renormalization group method, we investigate the
ground-state properties of a one-dimensional three-orbital Hubbard model on the
basis of a j-j coupling scheme. For , where is a parameter
to control cubic crystalline electric field effect, one orbital is itinerant,
while other two are localized. Due to the competition between itinerant and
localized natures, we obtain orbital ordering pattern which is sensitive to
, leading to a characteristic change of quadrupole state
into an incommensurate structure. At , all the three orbitals are
degenerate, but we observe a peak at in quadrupole
correlation, indicating a ferro-orbital state, and the peak at in
dipole correlation, suggesting an antiferromagnetic state. We
also discuss the effect of octupole on magnetic anisotropy.Comment: 4 pages, 3 figures, Proceedings of ASR-WYP-2005 (September 27-29,
2005, Tokai
Spin fluctuations probed by NMR in paramagnetic spinel LiVO: a self-consistent renormalization theory
Low frequency spin fluctuation dynamics in paramagnetic spinel LiVO,
a rare 3-electron heavy fermion system, is investigated. A parametrized
self-consistent renormalization (SCR) theory of the dominant AFM spin
fluctuations is developed and applied to describe temperature and pressure
dependences of the low- nuclear spin-lattice relaxation rate in this
material. The experimental data for available down to K are
well reproduced by the SCR theory, showing the development of AFM spin
fluctuations as the paramagnetic metal approaches a magnetic instability under
the applied pressure. The low- upturn of detected below 0.6 K under
the highest applied pressure of 4.74 GPa is explained as the nuclear spin
relaxation effect due to the spin freezing of magnetic defects unavoidably
present in the measured sample of LiVO.Comment: 11 pages, 2 figure
Effective Crystalline Electric Field Potential in a j-j Coupling Scheme
We propose an effective model on the basis of a - coupling scheme to
describe local -electron states for realistic values of Coulomb interaction
and spin-orbit coupling , for future development of microscopic
theory of magnetism and superconductivity in -electron systems, where
is the number of local electrons. The effective model is systematically
constructed by including the effect of a crystalline electric field (CEF)
potential in the perturbation expansion in terms of . In this paper,
we collect all the terms up to the first order of . Solving the
effective model, we show the results of the CEF states for each case of
=25 with symmetry in comparison with those of the Stevens
Hamiltonian for the weak CEF. In particular, we carefully discuss the CEF
energy levels in an intermediate coupling region with in the order
of 0.1 corresponding to actual -electron materials between the and
- coupling schemes. Note that the relevant energy scale of is the
Hund's rule interaction. It is found that the CEF energy levels in the
intermediate coupling region can be quantitatively reproduced by our modified
- coupling scheme, when we correctly take into account the corrections in
the order of in addition to the CEF terms and Coulomb interactions
which remain in the limit of =. As an application of the
modified - coupling scheme, we discuss the CEF energy levels of filled
skutterudites with symmetry.Comment: 12 pages, 7 figures. Typeset with jpsj2.cl
Double-Exchange Ferromagnetism and Orbital-Fluctuation-Induced Superconductivity in Cubic Uranium Compounds
A double-exchange mechanism for the emergence of ferromagnetism in cubic
uranium compounds is proposed on the basis of a - coupling scheme. The
idea is {\it orbital-dependent duality} of electrons concerning itinerant
and localized states in the cubic structure. Since
orbital degree of freedom is still active in the ferromagnetic phase,
orbital-related quantum critical phenomenon is expected to appear. In fact,
odd-parity p-wave pairing compatible with ferromagnetism is found in the
vicinity of an orbital ordered phase. Furthermore, even-parity d-wave pairing
with significant odd-frequency components is obtained. A possibility to observe
such exotic superconductivity in manganites is also discussed briefly.Comment: 4 pages, 4 figures. To appear in J. Phys. Soc. Jp
Fulde-Ferrell-Larkin-Ovchinnikov State in the absence of a Magnetic Field
We propose that in a system with pocket Fermi surfaces, a pairing state with
a finite total momentum q_tot like the Fulde-Ferrell-Larkin-Ovchinnikov state
can be stabilized even without a magnetic field. When a pair is composed of
electrons on a pocket Fermi surface whose center is not located at Gamma point,
the pair inevitably has finite q_tot. To investigate this possibility, we
consider a two-orbital model on a square lattice that can realize pocket Fermi
surfaces and we apply fluctuation exchange approximation. Then, by changing the
electron number n per site, we indeed find that such superconducting states
with finite q_tot are stabilized when the system has pocket Fermi surfaces.Comment: 4 pages, 5 figure
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