817 research outputs found
Thermal transport of the XXZ chain in a magnetic field
We study the heat conduction of the spin-1/2 XXZ chain in finite magnetic
fields where magnetothermal effects arise. Due to the integrability of this
model, all transport coefficients diverge, signaled by finite Drude weights.
Using exact diagonalization and mean-field theory, we analyze the temperature
and field dependence of the thermal Drude weight for various exchange
anisotropies under the condition of zero magnetization-current flow. First, we
find a strong magnetic field dependence of the Drude weight, including a
suppression of its magnitude with increasing field strength and a non-monotonic
field-dependence of the peak position. Second, for small exchange anisotropies
and magnetic fields in the massless as well as in the fully polarized regime
the mean-field approach is in excellent agreement with the exact
diagonalization data. Third, at the field-induced quantum critical line between
the para- and ferromagnetic region we propose a universal low-temperature
behavior of the thermal Drude weight.Comment: 9 pages REVTeX4 including 5 figures, revised version, refs. added,
typos correcte
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Setting of graded levels of a protein in yeast by a t-degron technique as applied to phosphoglycerate mutase
BACKGROUND: Setting of graded levels of a protein for in vivo studies by controlled gene expression has inconveniences, and we here explore the use of the t-degron technique instead. RESULTS: In a yeast t-degron (ubiquitin-argDHFR(ts))- phosphoglycerate mutase (GPM1) fusion strain, increasing periods of exposure to the non-permissive temperature 37°C, even in the presence of cycloheximide, gave decreasing function, as assessed at 23°C in vivo by glucose metabolism and confirmed by immunoblot. CONCLUSION: An ideal system would set a range of lower levels of a protein, do so without compensating protein synthesis, and give stable activity for in vitro comparisons. Although the first two aims appear obtainable, the third was not in this example of the application, limiting its uses for some but not all purposes
Comparative study of theoretical methods for nonequilibrium quantum transport
We present a detailed comparison of three different methods designed to
tackle nonequilibrium quantum transport, namely the functional renormalization
group (fRG), the time-dependent density matrix renormalization group (tDMRG),
and the iterative summation of real-time path integrals (ISPI). For the
nonequilibrium single-impurity Anderson model (including a Zeeman term at the
impurity site), we demonstrate that the three methods are in quantitative
agreement over a wide range of parameters at the particle-hole symmetric point
as well as in the mixed-valence regime. We further compare these techniques
with two quantum Monte Carlo approaches and the time-dependent numerical
renormalization group method.Comment: 19 pages, 7 figures; published versio
Interaction quantum quenches in the one-dimensional Fermi-Hubbard model with spin imbalance
Using the time-dependent density matrix renormalization group method and
exact diagonalization, we study the non-equilibrium dynamics of the
one-dimensional Fermi-Hubbard model following a quantum quench or a ramp of the
onsite interaction strength. For quenches from the non-interacting to the
attractive regime, we investigate the dynamical emergence of
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) correlations, which at finite spin
polarizations are the dominant two-body correlations in the ground state, and
their signatures in the pair quasi-momentum distribution function. We observe
that the post-quench double occupancy exhibits a maximum as the interaction
strength becomes of the order of the bandwidth. Finally, we study quenches and
ramps from attractive to repulsive interactions, which imprint FFLO
correlations onto repulsively bound pairs. We show that a quite short ramp time
is sufficient to wipe out the characteristic FFLO features in the post-quench
pair momentum distribution functions.Comment: 13 pages, 15 figures, minor revisions, version as publishe
Magnetic heat conductivity in : linear temperature dependence
We present experimental results for the thermal conductivity of the
pseudo 2-leg ladder material . The strong buckling of the ladder
rungs renders this material a good approximation to a Heisenberg-chain.
Despite a strong suppression of the thermal conductivity of this material in
all crystal directions due to inherent disorder, we find a dominant magnetic
contribution along the chain direction.
is \textit{linear} in temperature, resembling the
low-temperature limit of the thermal Drude weight of the
Heisenberg chain. The comparison of and
yields a magnetic mean free path of \AA, in good agreement with magnetic measurements.Comment: appears in PR
Bound states in weakly disordered spin ladders
We study the appearance of bound states in the spin gap of spin-1/2 ladders
induced by weak bond disorder. Starting from the strong-coupling limit, i.e.,
the limit of weakly coupled dimers, we perform a projection on the
single-triplet subspace and derive the position of bound states for the single
impurity problem of one modified coupling as well as for small impurity
clusters. The case of a finite concentration of impurities is treated with the
coherent-potential approximation in the strong-coupling limit and compared with
numerical results. Furthermore, we analyze the details in the structure of the
density of states and relate their origin to the influence of impurity
clusters.Comment: 2 pages, 1 figure. Proceedings of SCES'04, to appear in Physica
Coherent spin-current oscillations in transverse magnetic fields
We address the coherence of the dynamics of spin-currents with components
transverse to an external magnetic field for the spin-1/2 Heisenberg chain. We
study current autocorrelations at finite temperatures and the real-time
dynamics of currents at zero temperature. Besides a coherent Larmor
oscillation, we find an additional collective oscillation at higher
frequencies, emerging as a coherent many-magnon effect at low temperatures.
Using numerical and analytical methods, we analyze the oscillation frequency
and decay time of this coherent current-mode versus temperature and magnetic
field.Comment: 4 pages, 5 figures (and supplemental material: 4 pages, 6 figures
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