136 research outputs found
Nonlocal Effect of Local Nonmagnetic Impurity in High-Tc Superconductors: Induced Local Moment and Huge Residual Resistivity
We study a Hubbard model with a strong onsite impurity potential based on an
improved fluctuation-exchange (FLEX) approximation, which we call the GVI-FLEX
method. We find that (i) both local and staggered susceptibilities are strongly
enhanced around the impurity. By this reason, (ii) the quasiparticle lifetime
as well as the local density of states (DOS) are strongly suppressed in a wide
area around the impurity (like a Swiss cheese hole), which causes the ``huge
residual resistivity'' beyond the s-wave unitary scattering value. These
results by the GVI method naturally explains the various impurity effects in
HTSC's in a unified way, which had been a long-standing theoretical problem.Comment: 3 pages, submitted to ICM2006, Kyot
Physical Meaning of the Current Vertex Corrections: DC and AC Transport Phenomena in High-Tc Superconductors
Famous non-Fermi liquid-like behaviors of the transport phenomena in high-Tc
cuprates (Hall coefficient, magnetoresistance, thermoelectric power, Nernst
coefficient, etc) are caused by the current vertex corrections in neary
antiferromagnetic (AF) Fermi liquid, which was called the backflow by Landau.
We present a simple explaination why the backflow is prominent in strongly
correlated systems. In nearly AF Fermi liquid, R_H is enhanced by the backflow
because it changes the effective curvature of the Fermi surfaces. Therefore,
the relaxation time approximation is not appricalbe to a system near a magnetic
quantum critical point (QCP).Comment: 2 pages, submitted to proceedings of LT24, Figure 1 has been change
Anomalous Hall Effect in Orbital Kagome Lattice due to Non-collinearity:Significance of Orbital Aharonov-Bohm Effect
A new mechanism of spin structure-driven anomalous Hall effect (AHE) in
tilted ferromagnetic metals is proposed by taking account of the d-orbital
degree of freedom. We find that a conduction electron acquires a Berry phase
due to the complex d-orbital wavefunction, in the presence of non-collinear
spin structure and the spin orbit interaction. The AHE driven by this
orbital-derived Berry phase is much larger than the AHE induced by spin
chirality, and it naturally explains the salient features of spin
structure-driven AHE in pyrochlore NdMoO. Since the proposed AHE
can occur even for coplanar spin orders (), it is expected to emerge in
other interesting geometrically frustrated systems.Comment: 5 page
Spin fluctuations and weak pseudogap behaviors in Na_{0.35}CoO_2:renomarization of band structure
We analyze the normal electronic states of NaCoO based on the
multi-orbital Hubbard model using the FLEX approximation. The fundamental
electronic property of this system is drastically changed by the presence or
absence of the small hole pockets associated with the orbital. This
change of the Fermi surface topology may be caused by the crystalline electric
splitting due to the trigonal distortion. When small hole pockets are absent,
the weak pseudogap bahaviors appear in the density of states and the uniform
spin susceptibility, which are observed by recent experiments. We estimate the
mass enhancement factor of quasiparticle . This result
suppports recent ARPES measurements.Comment: 2 pages, 2 figures, submitted to proceedings of LT24, Orlando, FL,
August 2005; added referenc
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