2,906 research outputs found
Spin fluctuations and superconductivity in noncentrosymmetric heavy fermion systems CeRhSi and CeIrSi
We study the normal and the superconducting properties in noncentrosymmetric
heavy fermion superconductors CeRhSi and CeIrSi. For the normal state,
we show that experimentally observed linear temperature dependence of the
resistivity is understood through the antiferromagnetic spin fluctuations near
the quantum critical point (QCP) in three dimensions. For the superconducting
state, we derive a general formula to calculate the upper critical field
, with which we can treat the Pauli and the orbital depairing effect on
an equal footing. The strong coupling effect for general electronic structures
is also taken into account. We show that the experimentally observed features
in , the huge value up to 30(T), the downward
curvatures, and the strong pressure dependence, are naturally understood as an
interplay of the Rashba spin-orbit interaction due to the lack of inversion
symmetry and the spin fluctuations near the QCP. The large anisotropy between
and is explained in terms of
the spin-orbit interaction. Furthermore, a possible realization of the
Fulde-Ferrell- Larkin-Ovchinnikov state for is studied. We
also examine effects of spin-flip scattering processes in the pairing
interaction and those of the applied magnetic field on the spin fluctuations.
We find that the above mentioned results are robust against these effects. The
consistency of our results strongly supports the scenario that the
superconductivity in CeRhSi and CeIrSi is mediated by the spin
fluctuations near the QCP.Comment: 21pages, 13figures, to be published in Phys. Rev.
Anomalous magnetic properties near Mott transition in Kagom\'e lattice Hubbard model
We investigate the characteristics of the metallic phase near the Mott
transition in the Kagom\'e lattice Hubbard model using the cellular dynamical
mean field theory. By calculating the specific heat and spin correlation
functions, we demonstrate that the quasiparticles show anomalous properties in
the metallic phase close to the Mott transition. We find clear evidence for the
multi-band heavy quasiparticles in the specific heat, which gives rise to
unusual temperature dependence of the spin correlation functions.Comment: 2 pages, 3 figures, accepted for publication in J. Mag. Mag. Mater.
(Proceedings of the ICM, Kyoto, Japan, August 2006
Oscillatory Spin Polarization and Magneto-Optic Kerr Effect in Fe3O4 Thin Films on GaAs(001)
The spin dependent properties of epitaxial Fe3O4 thin films on GaAs(001) are
studied by the ferromagnetic proximity polarization (FPP) effect and
magneto-optic Kerr effect (MOKE). Both FPP and MOKE show oscillations with
respect to Fe3O4 film thickness, and the oscillations are large enough to
induce repeated sign reversals. We attribute the oscillatory behavior to
spin-polarized quantum well states forming in the Fe3O4 film. Quantum
confinement of the t2g states near the Fermi level provides an explanation for
the similar thickness dependences of the FPP and MOKE oscillations.Comment: to appear in Phys. Rev. Let
Superconductivity induced by longitudinal ferromagnetic fluctuations in UCoGe
From detailed angle-resolved NMR and Meissner measurements on a ferromagnetic
(FM) superconductor UCoGe (T_Curie ~ 2.5 K and T_SC ~ 0.6 K), we show that
superconductivity in UCoGe is tightly coupled with longitudinal FM spin
fluctuations along the c axis. We found that magnetic fields along the c axis
(H || c) strongly suppress the FM fluctuations and that the superconductivity
is observed in the limited magnetic field region where the longitudinal FM spin
fluctuations are active. These results combined with model calculations
strongly suggest that the longitudinal FM spin fluctuations tuned by H || c
induce the unique spin-triplet superconductivity in UCoGe. This is the first
clear example that FM fluctuations are intimately related with
superconductivity.Comment: 4 pages, 5 figures, to appear in PR
Finite-temperature Mott transitions in multi-orbital Hubbard model
We investigate the Mott transitions in the multi-orbital Hubbard model at
half-filling by means of the self-energy functional approach. The phase
diagrams are obtained at finite temperatures for the Hubbard model with up to
four-fold degenerate bands. We discuss how the first-order Mott transition
points and as well as the critical temperature depend
on the orbital degeneracy. It is elucidated that enhanced orbital fluctuations
play a key role to control the Mott transitions in the multi-orbital Hubbard
model.Comment: 8 pages, 7 figure
Epitaxial EuO Thin Films on GaAs
We demonstrate the epitaxial growth of EuO on GaAs by reactive molecular beam
epitaxy. Thin films are grown in an adsorption-controlled regime with the aid
of an MgO diffusion barrier. Despite the large lattice mismatch, it is shown
that EuO grows well on MgO(001) with excellent magnetic properties. Epitaxy on
GaAs is cube-on-cube and longitudinal magneto-optic Kerr effect measurements
demonstrate a large Kerr rotation of 0.57{\deg}, a significant remanent
magnetization, and a Curie temperature of 69 K.Comment: 5 pages, 3 figure
Crossover Phenomena in the One-Dimensional SU(4) Spin-Orbit Model under Magnetic Fields
We study the one-dimensional SU(4) exchange model under magnetic fields,
which is the simplest effective Hamiltonian in order to investigate the quantum
fluctuations concerned with the orbital degrees of freedom in coupled
spin-orbit systems. The Bethe ansatz approaches and numerical calculations
using the density matrix renormalization group method are employed. The main
concern of the paper is how the system changes from the SU(4) to the SU(2)
symmetric limit as the magnetic field is increased. For this model the
conformal field theory predicts an usual behavior: there is a jump of the
critical exponents just before the SU(2) limit. For a finite-size system,
however, the orbital-orbital correlation functions approach continuously to the
SU(2) limit after interesting crossover phenomena. The crossover takes place in
the magnetization range of 1/3 1/2 for the system with 72 sites studied
in this paper.Comment: 8 pages, 6 Postscript figures, REVTeX, submitted to Phys. Rev.
Spin, charge and orbital fluctuations in a multi-orbital Mott insulator
The two-orbital degenerate Hubbard model with distinct hopping integrals is
studied by combining dynamical mean-field theory with quantum Monte Carlo
simulations. The role of orbital fluctuations for the nature of the Mott
transition is elucidated by examining the temperature dependence of spin,
charge and orbital susceptibilities as well as the one-particle spectral
function. We also consider the effect of the hybridization between the two
orbitals, which is important particularly close to the Mott transition points.
The introduction of the hybridization induces orbital fluctuations, resulting
in the formation of a Kondo-like heavy-fermion behavior, similarly to
electron systems, but involving electrons in bands of comparable width.Comment: 8 pages, 9 figure
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