10,232 research outputs found
Field-induced spin-density-wave phases in TMTSF organic conductors: quantization versus non-quantization
We study the magnetic-field-induced spin-density-wave (FISDW) phases in TMTSF
organic conductors in the framework of the quantized nesting model. In
agreement with recent suggestions, we find that the SDW wave-vector
deviates from its quantized value near the transition temperature for all
phases with quantum numbers . Deviations from quantization are more
pronounced at low pressure and higher and may lead to a suppression of the
first-order transitions for . Below a critical pressure, we
find that the N=0 phase invades the entire phase diagram in accordance with
earlier experiments. We also show that at T=0, the quantization of
and hence the Hall conductance is always exact. Our results suggest a novel
phase transition/crossover at intermediate temperatures between phases with
quantized and non-quantized .Comment: 4 pages, 4 figures, Revte
Effective action and collective modes in quasi-one-dimensional spin-density-wave systems
We derive the effective action describing the long-wavelength low-energy
collective modes of quasi-one-dimensional spin-density-wave (SDW) systems,
starting from the Hubbard model within weak coupling approximation. The
effective action for the spin-wave mode corresponds to an anisotropic
non-linear sigma model together with a Berry phase term. We compute the spin
stiffness and the spin-wave velocity. We also obtain the effective action for
the sliding mode (phason) taking into account the density fluctuations from the
outset and in presence of a weak external electromagnetic field. This leads to
coupled equations for the phase of the SDW condensate and the charge density
fluctuations. We also calculate the conductivity and the density-density
correlation function.Comment: 16 pages, Resubmitted to Physical Review B with minor suggested
change
An anomalous magnetic phase transition at 10 K in Nd7Rh3
The compound, Nd7Rh3, crystallizing in Th7Fe3-type hexagonal structure, has
been shown recently by us to exhibit a signature of magnetic phase-coexistence
phenomenon below 10 K after a field cycling, uncharacteristic of stoichiometric
intermetallic compounds, bearing a relevance to the trends in the field of
electronic phase-separation. In order to characterize this compound further, we
have carried out dc magnetic susceptibility (chi), electrical resistivity,
magnetoresistance and heat-capacity measurements as a function temperature (T=
1.8 to 300 K). The results reveal that this compound exhibits another unusual
finding at the 10K-transition in the sense that the plot of chi(T) shows a
sharp increase in the field-cooled cycle, whereas the zero-field-cooled curve
shows a downturn below the transition. In addition, the sign of
magnetoresistance is negative and the magnitude is large over a wide
temperature range in the vicinity of magnetic ordering temperature, with a
sharp variation at 10 K. The results indicate that the transition below 10 K is
first-order in its character.Comment: Appeared in JPCM (Letters) 18 (2006) L40
One-dimensional itinerant ferromagnets with Heisenberg symmetry and the ferromagnetic quantum critical point
We study one-dimensional itinerant ferromagnets with Heisenberg symmetry near
a ferromagnetic quantum critical point. It is shown that the Berry phase term
arises in the effective action of itinerant ferromagnets when the full SU(2)
symmetry is present. We explicitly demonstrate that dynamical critical exponent
of the theory with the Berry term is in the sense of
expansion, as previously discovered in the Ising limit. It appears,
however, that the universality class at the interacting fixed point is not the
same. We point out that even though the critical theory in the Ising limit can
be obtained by the standard Hertz-Millis approach, the Heisenberg limit is
expected to be different. We also calculate the exact electron Green functions
and near the transition in a range of temperature, which
can be used for experimental signatures of the associated critical points.Comment: Replaced with final version accepted in PRB; minor changes from the
previous versio
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