90 research outputs found
Field-induced magnetic behavior in quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8: A single-crystal neutron diffraction study
BaCo2V2O8 is a nice example of a quasi-one-dimensional quantum spin system
that can be described in terms of Tomonaga-Luttinger liquid physics. This is
explored in the present study where the magnetic field-temperature phase
diagram is thoroughly established up to 12 T using single-crystal neutron
diffraction. The transition from the N\'eel phase to the incommensurate
longitudinal spin density wave (LSDW) phase through a first-order transition,
as well as the critical exponents associated with the paramagnetic to ordered
phase transitions, and the magnetic order both in the N\'eel and in the LSDW
phase are determined, thus providing a stringent test for the theory.Comment: 17 pages with 15 figure
Ammi visnaga (L.) Lam. (Apiaceae), a new taxon in Croatian flora
During floristic research into the island of Bra~ (Dalmatia, Croatia) in 2010, Ammi visnaga (L.) Lam. (Apiaceae), a new neophyte for Croatia was found in several localities and natural habitats. At the altitude of 380–460 m above sea level, mostly in habitats disturbed by humans, the located populations were composed of numerous and vital specimens in blooms and with fruits. The gradual and successful integration of this species into the natural vegetation was noticed, particularly in grasslands of the association Brachypodio retuso-Trifolietum stellati Horvati} 1958 and macchia of the association Fraxino orno-Quercetum ilicis Horvati} (1956) 1958
and mesons in the Dyson-Schwinger approach at finite temperature
We study the temperature dependence of the pseudoscalar meson properties in a
relativistic bound-state approach exhibiting the chiral behavior mandated by
QCD. Concretely, we adopt the Dyson-Schwinger approach with a rank-2 separable
model interaction. After extending the model to the strange sector and fixing
its parameters at zero temperature, T=0, we study the T-dependence of the
masses and decay constants of all ground-state mesons in the pseudoscalar
nonet. Of chief interest are and . The influence of the QCD
axial anomaly on them is successfully obtained through the Witten-Veneziano
relation at T=0. The same approach is then extended to T>0, using lattice QCD
results for the topological susceptibility. The most conspicuous finding is an
increase of the mass around the chiral restoration temperature
, which would suggest a suppression of production in
relativistic heavy-ion collisions. The increase of the mass may
also indicate that the extension of the Witten-Veneziano relation to finite
temperatures becomes unreliable around and above . Possibilities of
an improved treatment are discussed.Comment: 13 pages, 15 figure
Huge Transverse Magnetization in the Field-Induced Phase of the Antiferromagnetic Molecular Wheel CsFe8
The 1H-NMR spectrum and nuclear relaxation rate 1/T_1 in the
antiferromagnetic wheel CsFe8 were measured to characterize the previously
observed magnetic field-induced low-temperature phase around the level crossing
at 8 T. The data show that the phase is characterized by a huge staggered
transverse polarization of the electronic Fe spins, and the opening of a gap,
providing microscopic evidence for the interpretation of the phase as a
field-induced magneto-elastic instability.Comment: 5 pages, 4 figures, REVTEX4, to appear in PR
Iterated perturbation theory for the attractive Holstein and Hubbard models
A strictly truncated (weak-coupling) perturbation theory is applied to the
attractive Holstein and Hubbard models in infinite dimensions. These results
are qualified by comparison with essentially exact Monte Carlo results. The
second order iterated perturbation theory is shown to be quite accurate in
calculating transition temperatures for retarded interactions, but is not as
accurate for the self energy or the irreducible vertex functions themselves.
Iterated perturbation theory is carried out thru fourth order for the Hubbard
model. The self energy is quite accurately reproduced by the theory, but the
vertex functions are not. Anomalous behavior occurs near half filling because
the iterated perturbation theory is not a conserving approximation. (REPLACED
WITH UUENCODED FIGURES AT THE END. THE TEXT IS UNCHANGED)Comment: 27 pages, RevTex (figures appended at end
Quantum-critical spin dynamics in quasi-one-dimensional antiferromagnets
By means of nuclear spin-lattice relaxation rate 1/T1, we follow the spin
dynamics as a function of the applied magnetic field in two gapped
one-dimensional quantum antiferromagnets: the anisotropic spin-chain system
NiCl2-4SC(NH2)2 and the spin-ladder system (C5H12N)2CuBr4. In both systems,
spin excitations are confirmed to evolve from magnons in the gapped state to
spinons in the gapples Tomonaga-Luttinger-liquid state. In between, 1/T1
exhibits a pronounced, continuous variation, which is shown to scale in
accordance with quantum criticality. We extract the critical exponent for 1/T1,
compare it to the theory, and show that this behavior is identical in both
studied systems, thus demonstrating the universality of quantum critical
behavior
Formulae for zero-temperature conductance through a region with interaction
The zero-temperature linear response conductance through an interacting
mesoscopic region attached to noninteracting leads is investigated. We present
a set of formulae expressing the conductance in terms of the ground-state
energy or persistent currents in an auxiliary system, namely a ring threaded by
a magnetic flux and containing the correlated electron region. We first derive
the conductance formulae for the noninteracting case and then give arguments
why the formalism is also correct in the interacting case if the ground state
of a system exhibits Fermi liquid properties. We prove that in such systems,
the ground-state energy is a universal function of the magnetic flux, where the
conductance is the only parameter. The method is tested by comparing its
predictions with exact results and results of other methods for problems such
as the transport through single and double quantum dots containing interacting
electrons. The comparisons show an excellent quantitative agreement.Comment: 18 pages, 18 figures; to appear in Phys. Rev.
Many-body theory of the quantum mirage
In recent scanning tunneling microscopy experiments, confinement in an
elliptical corral has been used to project the Kondo effect from one focus to
the other one. I solve the Anderson model at arbitrary temperatures, for an
impurity hybridized with eigenstates of an elliptical corral, each of which has
a resonant level width delta. This width is crucial. If delta < 20 meV, the
Kondo peak disappears, while if delta > 80 meV, the mirage disappears. For
particular conditions, a stronger mirage with the impurity out of the foci is
predicted.Comment: 5 pages, 5 figures. Some clarifications of the method added, and a
reference included to show that the hybridization of the impurity with bulk
states can be neglecte
Soliton Lattices in the Incommensurate Spin-Peierls Phase: Local Distortions and Magnetizations
It is shown that nonadiabatic fluctuations of the soliton lattice in the
spin-Peierls system CuGeO_3 lead to an important reduction of the NMR line
widths. These fluctuations are the zero-point motion of the massless phasonic
excitations. Furthermore, we show that the discrepancy of X-ray and NMR soliton
widths can be understood as the difference between a distortive and a magnetic
width. Their ratio is controlled by the frustration of the spin system. By this
work, theoretical and experimental results can be reconciled in two important
points.Comment: 9 pages, 5 figures included, Revtex submitted to Physical Review
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