125 research outputs found
Resistivity and optical conductivity of cuprates within the t-J model
The optical conductivity and the d.c. resistivity
within the extended t-J model on a square lattice, as relevant to high-
cuprates, are reinvestigated using the exact-diagonalization method for small
systems, improved by performing a twisted boundary condition averaging. The
influence of the next-nearest-neighbor hopping is also considered. The
behaviour of results at intermediate doping is consistent with a
marginal-Fermi-liquid scenario and in the case of for follows
the power law with consistent
with experiments. At low doping for develops a
shoulder at , consistent with the observed mid-infrared
peak in experiments, accompanied by a shallow dip for . This
region is characterized by the resistivity saturation, whereas a more coherent
transport appears at producing a more pronounced decrease in
. The behavior of the normalized resistivity is within a
factor of 2 quantitatively consistent with experiments in cuprates.Comment: 8 pages, 10 figure
Breakdown of the Luttinger sum rule within the Mott-Hubbard insulator
The validity of the Luttinger sum rule is investigated within the prototype
tight-binding model of interacting fermions in one dimension, i.e., the t-V
model including the next-nearest neighbor hopping t' in order to break the
particle-hole symmetry. Scaling analysis of finite-system results at
half-filling reveals evident breakdown of the sum rule in the regime of large
gap at V >> t, while the sum rule appears to recover together with vanishing of
the Mott-Hubbard gap.Comment: 4 pages, 5 figure
Conductivity in a disordered one-dimensional system of interacting fermions
Dynamical conductivity in a disordered one-dimensional model of interacting
fermions is studied numerically at high temperatures and in the
weak-interaction regime in order to find a signature of many-body localization
and vanishing d.c. transport coefficients. On the contrary, we find in the
regime of moderately strong local disorder that the d.c. conductivity sigma0
scales linearly with the interaction strength while being exponentially
dependent on the disorder. According to the behavior of the charge stiffness
evaluated at the fixed number of particles, the absence of the many-body
localization seems related to an increase of the effective localization length
with the interaction.Comment: 4 pages, 5 figures, submitted to PR
Coexistence of Anomalous and Normal Diffusion in Integrable Mott Insulators
We study the finite-momentum spin dynamics in the one-dimensional XXZ spin
chain within the Ising-type regime at high temperatures using density
autocorrelations within linear response theory and real-time propagation of
nonequilibrium densities. While for the nonintegrable model results are well
consistent with normal diffusion, the finite-size integrable model unveils the
coexistence of anomalous and normal diffusion in different regimes of time. In
particular, numerical results show a Gaussian relaxation at smallest nonzero
momenta which we relate to nonzero stiffness in a grand canonical ensemble. For
larger but still small momenta normal-like diffusion is recovered. Similar
results for the model of impenetrable particles also help to resolve rather
conflicting conclusions on transport in integrable Mott insulators.Comment: 5 pages, 4 figure
Eigenstate thermalization within isolated spin-chain systems
The thermalization phenomenon and many-body quantum statistical properties
are studied on the example of several observables in isolated spin-chain
systems, both integrable and generic non-integrable ones. While diagonal matrix
elements for non-integrable models comply with the eigenstate thermalization
hypothesis (ETH), the integrable systems show evident deviations and similarity
to properties of noninteracting many-fermion models. The finite-size scaling
reveals that the crossover between two regimes is given by a scale closely
related to the scattering length. Low-frequency off-diagonal matrix elements
related to d.c. transport quantities in a generic system also follow the
behavior analogous to the ETH, however unrelated to the one of diagonal
elements
Magnetic response of nonmagnetic impurities in cuprates
A theory of the local magnetic response of a nonmagnetic impurity in a doped
antiferromagnet, as relevant to the normal state in cuprates, is presented. It
is based on the assumption of the overdamped collective mode in the bulk system
and on the evidence, that equal-time spin correlations are only weakly
renormalized in the vicinity of the impurity. The theory relates the Kondo-like
behavior of the local susceptibility to the anomalous temperature dependence of
the bulk magnetic susceptibility, where the observed increase of the Kondo
temperature with doping reflects the crossover to the Fermi liquid regime and
the spatial distribution of the magnetization is given by bulk
antiferromagnetic correlations.Comment: 5 pages, 3 figure
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