1,382 research outputs found
Low-temperature electrical resistivity in paramagnetic spinel LiV2O4
The 3d electron spinel compound LiV2O4 exhibits heavy fermion behaviour below
30K which is related to antiferromagnetic spin fluctuations strongly enhanced
in an extended region of momentum space. This mechanism explains enhanced
thermodynamic quantities and nearly critical NMR relaxation in the framework of
the selfconsistent renormalization (SCR) theory. Here we show that the low-T
Fermi liquid behaviour of the resistivity and a deviation from this behavior
for higher T may also be understood within that context. We calculate the
temperature dependence of the electrical resistivity \rho(T) assuming that two
basic mechanisms of the quasiparticle scattering, resulting from impurities and
spin-fluctuations, operate simultaneously at low temperature. The calculation
is based on the variational principle in the form of a perturbative series
expansion for \rho(T). A peculiar behavior of \rho(T) in LiV2O4 is related to
properties of low-energy spin fluctuations whose T-dependence is obtained from
SCR theory.Comment: 10 pages, 3 figures, to appear in Phys. Rev.
Negative effective mass transition and anomalous transport in power-law hopping bands
We study the stability of spinless Fermions with power law hopping . It is shown that at precisely , the
dispersive inflection point coalesces with the band minimum and the charge
carriers exhibit a transition into negative effective mass regime, characterized by retarded transport in the presence of an electric field.
Moreover, bands with must be accompanied by counter-carriers with
, having a positive band curvature, thus stabilizing the system
in order to maintain equilibrium conditions and a proper electrical response.
We further examine the semi-classical transport and response properties,
finding an infrared divergent conductivity for 1/r hopping(). The
analysis is generalized to regular lattices in dimensions = 1, 2, and 3.Comment: 6 pages. 2 figure
Probability-based comparison of quantum states
We address the following state comparison problem: is it possible to design
an experiment enabling us to unambiguously decide (based on the observed
outcome statistics) on the sameness or difference of two unknown state
preparations without revealing complete information about the states? We find
that the claim "the same" can never be concluded without any doubts unless the
information is complete. Moreover, we prove that a universal comparison (that
perfectly distinguishes all states) also requires complete information about
the states. Nevertheless, for some measurements, the probability distribution
of outcomes still allows one to make an unambiguous conclusion regarding the
difference between the states even in the case of incomplete information. We
analyze an efficiency of such a comparison of qudit states when it is based on
the SWAP-measurement. For qubit states, we consider in detail the performance
of special families of two-valued measurements enabling us to successfully
compare at most half of the pairs of states. Finally, we introduce almost
universal comparison measurements which can distinguish almost all
non-identical states (up to a set of measure zero). The explicit form of such
measurements with two and more outcomes is found in any dimension.Comment: 12 pages, 6 figures, 1 table, some results are extende
Effects of thermal- and spin- fluctuations on the band structure of purple bronze LiMoO
The band structures of ordered and thermally disordered
LiMoO are calculated by use of ab-initio DFT-LMTO method. The
unusual, very 1-dimensional band dispersion obtained in previous band
calculations is confirmed for the ordered structure, and the overall band
structure agrees reasonably with existing photoemission data. Dispersion and
bandstructure perpendicular to the main dispersive direction is obtained. A
temperature dependent band broadening is calculated from configurations with
thermal disorder of the atomic positions within the unit cell. This leads a
band broadening of the two bands at the Fermi energy which can become
comparable to their energy separation. The bands are particularly sensitive to
in-plane movements of Mo sites far from the Li-sites, where the
density-of-states is highest. The latter fact makes the effect of Li vacancies
on the two bands relatively small. Spin-polarized band results for the ordered
structure show a surprisingly large exchange enhancement on the high DOS Mo
sites. Consequences for spin fluctuations associated with a cell doubling along
the conducting direction are discussed
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