83 research outputs found
Role of disorder in the Mott-Hubbard transition
We investigate the role of disorder in the Mott-Hubbard transition based on
the slave-rotor representation of the Hubbard model, where an electron is
decomposed into a fermionic spinon for a spin degree of freedom and a bosonic
rotor (chargon) for a charge degree of freedom. In the absence of disorder the
Mott-Hubbard insulator is assumed to be the spin liquid Mott insulator in terms
of gapless spinons near the Fermi surface and gapped chargons interacting via
U(1) gauge fields. We found that the Mott-Hubbard critical point becomes
unstable as soon as disorder is turned on. As a result, a disorder critical
point appears to be identified with the spin liquid glass insulator to the
Fermi liquid metal transition, where the spin liquid glass consists of the U(1)
spin liquid and the chargon glass. We expect that glassy behaviors of charge
fluctuations can be measured by the optical spectra in the insulating phase of
an organic material . Furthermore, since
the Mott-Anderson critical point depends on the spinon conductivity,
universality in the critical exponents may not be found
Dynamical Magnetic Susceptibilities in Cu Benzoate
Recent experiments on the quasi 1-D antiferromagnet Cu Benzoate revealed a
magentic field induced gap coexisting with (ferro)magnetic order. A theory
explaining these findings has been proposed by Oshikawa and Affleck. In the
present work we discuss consequences of this theory for inelastic neutron
scattering experiments by calculating the dynamical magnetic susceptibilities
close to the antiferromagnetic wave vector by the formfactor method.Comment: 6 pages of revtex, 9 figures, extended comparison with experimen
Ladder-like optical conductivity in the spin-fermion model
In the nested limit of the spin-fermion model for the cuprates,
one-dimensional physics in the form of half-filled two-leg ladders emerges. We
show that the renormalization group flow of the corresponding ladder is towards
the d-Mott phase, a gapped spin-liquid with short-ranged d-wave pairing
correlations, and reveals an intermediate SO(5)SO(3) symmetry. We use
the results of the renormalization group in combination with a memory-function
approach to calculate the optical conductivity of the spin-fermion model in the
high-frequency regime, where processes within the hot spot region dominate the
transport. We argue that umklapp processes play a major role. For finite
temperatures, we determine the resistivity in the zero-frequency (dc) limit.
Our results show an approximate linear temperature dependence of the
resistivity and a conductivity that follows a non-universal power law. A
comparison to experimental data supports our assumption that the conductivity
is dominated by the antinodal contribution above the pseudogap.Comment: 11+2 pages, 8 figure
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