1,242 research outputs found

### Finite-Temperature Mott Transition in the Two-Dimensional Hubbard Model

Mott transitions are studied in the two-dimensional Hubbard model by a
non-perturbative theory of correlator projection that systematically includes
spatial correlations into the dynamical mean-field approximation. Introducing a
nonzero second-neighbor transfer, a first-order Mott transition appears at
finite temperatures and ends at a critical point or curve.Comment: 2 pages, to appear in J. Mag. Mag. Mat. as proceedings of the
International Conference on Magnetism 200

### Gauge covariant formulation of Wigner representation through deformational quantization --Application to Keldysh formalism with electromagnetic field--

We developed a gauge-covariant formulation of the non-equilibrium Green
function method for the dynamical and/or non-uniform electromagnetic field by
means of the deformational quantization method. Such a formulation is realized
by replacing the Moyal product in the so-called Wigner space by the star
product, and facilitates the order-by-order calculation of a gauge-invariant
observable in terms of the electromagnetic field. An application of this
formalism to the linear response theory is discussed

### Intrinsic vs. extrinsic anomalous Hall effect in ferromagnets

A unified theory of the anomalous Hall effect (AHE) is presented for
multi-band ferromagnetic metallic systems with dilute impurities. In the clean
limit, the AHE is mostly due to the extrinsic skew-scattering. When the Fermi
level is located around anti-crossing of band dispersions split by spin-orbit
interaction, the intrinsic AHE to be calculated ab initio is resonantly
enhanced by its non-perturbative nature, revealing the extrinsic-to-intrinsic
crossover which occurs when the relaxation rate is comparable to the spin-orbit
interaction energy.Comment: 5 pages including 4 figures, RevTex; minor changes, to appaer in
Phys. Rev. Let

### Disorder effect on the localization/delocalization in incommensurate potential

The interplay between incommensurate (IC) and random potentials is studied in
a two-dimensional symplectic model with the focus on
localization/delocalization problem. With the IC potential only, there appear
wavefunctions localized along the IC wavevector while extended perpendicular to
it. Once the disorder potential is introduced, these turn into two-dimensional
anisotropic metallic states beyond the scale of the elastic mean free path, and
eventually becomes localized in both directions at a critical strength of the
disorder. Implications of these results to the experimental observation of the
IC-induced localization is discussed.Comment: 4 pages, 3 figures (7 files), RevTe

### Theory of Electron Differentiation, Flat Dispersion and Pseudogap Phenomena

Aspects of electron critical differentiation are clarified in the proximity
of the Mott insulator. The flattening of the quasiparticle dispersion appears
around momenta $(\pi,0)$ and $(0,\pi)$ on square lattices and determines the
criticality of the metal-insulator transition with the suppressed coherence in
that momentum region of quasiparticles. Such coherence suppression at the same
time causes an instability to the superconducting state if a proper incoherent
process is retained. The d-wave pairing interaction is generated from such
retained processes without disturbance from the coherent single-particle
excitations. Pseudogap phenomena widely observed in the underdoped cuprates are
then naturally understood from the mode-mode coupling of d-wave
superconducting(dSC) fluctuations with antiferromagnetic ones. When we assume
the existence of a strong d-wave pairing force repulsively competing with
antiferromagnetic(AFM) fluctuations under the formation of flat and damped
single-particle dispersion, we reproduce basic properties of the pseudogap seen
in the magnetic resonance, neutron scattering, angle resolved photoemission and
tunneling measurements in the cuprates.Comment: 9 pages including 2 figures, to appear in J. Phys. Chem. Solid

### Renormalization of the electron-phonon coupling in the one-band Hubbard model

We investigate the effect of electronic correlations on the coupling of
electrons to Holstein phonons in the one-band Hubbard model. We calculate the
static electron-phonon vertex within linear response of Kotliar-Ruckenstein
slave-bosons in the paramagnetic saddle-point approximation. Within this
approach the on-site Coulomb interaction U strongly suppresses the coupling to
Holstein phonons at low temperatures. Moreover the vertex function does not
show particularly strong forward scattering. Going to larger temperatures
kT\sim t we find that after an initial decrease with U, the electron-phonon
coupling starts to increase with U, confirming a recent result of Cerruti,
Cappelluti, and Pietronero. We show that this behavior is related to an unusual
reentrant behavior from a phase separated to a paramagnetic state upon
decreasing the temperature.Comment: 4 pages, 6 figure

### Mott Transition vs Multicritical Phenomenon of Superconductivity and Antiferromagnetism -- Application to $\kappa$-(BEDT-TTF)$_2$X --

Interplay between the Mott transition and the multicritical phenomenon of
d-wave superconductivity (SC) and antiferromagnetism (AF) is studied
theoretically. We describe the Mott transition, which is analogous to a
liquid-gas phase transition, in terms of an Ising-type order parameter $\eta$.
We reveal possible mean-field phase diagrams produced by this interplay.
Renormalization group analysis up to one-loop order gives flows of coupling
constants, which in most cases lead to fluctuation-induced first-order phase
transitions even when the SO(5) symmetry exists betwen the SC and AF. Behaviors
of various physical quantities around the Mott critical point are predicted.
Experiments in $\kappa$-(BEDT-TTF)$_2$X are discussed from this viewpoint.Comment: 4 pages, 9 figures, to appear in J. Phys. Soc. Jp

### Temperature dependent magnetotransport around $\nu$= 1/2 in ZnO heterostructures

The sequence of prominent fractional quantum Hall states up to $\nu$=5/11
around $\nu$=1/2 in a high mobility two-dimensional electron system confined at
oxide heterointerface (ZnO) is analyzed in terms of the composite fermion
model. The temperature dependence of \Rxx oscillations around $\nu$=1/2
yields an estimation of the composite fermion effective mass, which increases
linearly with the magnetic field. This mass is of similar value to an enhanced
electron effective mass, which in itself arises from strong electron
interaction. The energy gaps of fractional states and the temperature
dependence of \Rxx at $\nu$=1/2 point to large residual interactions between
composite fermions.Comment: 5 pages, 4 Figure

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