418 research outputs found
Competing Interactions, the Renormalization Group and the Isotropic-Nematic Phase Transition
We discuss 2D systems with Ising symmetry and competing interactions at
different scales. In the framework of the Renormalization Group, we study the
effect of relevant quartic interactions. In addition to the usual constant
interaction term, we analyze the effect of quadrupole interactions in the self
consistent Hartree approximation. We show that in the case of repulsive
quadrupole interaction, there is a first order phase transition to a stripe
phase in agreement with the well known Brazovskii result. However, in the case
of attractive quadrupole interactions there is an isotropic-nematic second
order transition with higher critical temperature.Comment: 4 pages, no figures, version to be published in Physical Review
Letters. Some scaling dimensions corrected, conclusions are the sam
A Field Theory for Fermionic Ladder with Generic Intrachain Interactions
An effective low energy field theory is developed for a system of two chains.
The main novelty of the approach is that it allows to treat generic intrachain
repulsive interactions of arbitrary strength. The chains are coupled by a
direct tunneling and four-fermion interactions. At low energies the individual
chains are described as Luttinger liquids with an arbitrary ratio of spin
and charge velocities. A judicious choice of the basis for the decoupled
chains greatly simplifies the description and allows one to separate high and
low energy degrees of freedom. In a direct analogy to the bulk cuprates the
resulting effective field theory distinguishes between three qualitatively
different regimes: (i) small doping (), (ii) optimal doping () and (iii) large doping (). I discuss the excitation
spectrum and derive expressions for the electron spectral function which turns
out to be highly incoherent. The degree of incoherence increases when one
considers an array of ladders (stripe phase).Comment: 32 pages, 4 figures. A section explaining adiabatic approximation is
modified. Typos correcte
Nature of superconducting state in the new phase in (TMTSF)PF under pressure
The unusual phase has been recently observed in the organic material
(TMTSF)PF, where superconductivity (SC) coexists with spin-density
wave (SDW) in the pressure interval below the first order
transition into SC or normal metal phase. Assuming that the coexistence takes
place on the microscopic scale, we consider the properties of the intermediate
phase. We show that the new superconducting state inside SDW phase just above
must bear a triplet pairing.Comment: 4 pages, 1 figur
Statistics of charged solitons and formation of stripes
The 2-fold degeneracy of the ground state of a quasi-one-dimensional system
allows it to support topological excitations such as solitons. We study the
combined effects of Coulomb interactions and confinement due to interchain
coupling on the statistics of such defects. We concentrate on a 2D case which
may correspond to monolayers of polyacetylene or other charge density waves.
The theory is developped by a mapping to the 2D Ising model with long-range
4-spin interactions. The phase diagram exhibits deconfined phases for liquids
and Wigner crystals of kinks and confined ones for bikinks. Also we find
aggregated phases with either infinite domain walls of kinks or finite rods of
bikinks. Roughening effects due to both temperature and Coulomb repulsion are
observed. Applications may concern the melting of stripes in doped correlated
materials.Comment: 16 pages, 7 figure
Nonlinear conduction of sliding electronic crystals: Charge and Spin Density Waves
A model of local metastable states due to the pinning induces plastic
deformations allows to describe the nonlinear I-V curves in sliding density
waves -DW. With increasing the DW velocity v, the metastable states of
decreasing lifetimes ~1/v are accessed. The characteristic second threshold
field is reached when configurations of shortest life time are accessed by the
fast moving DW. Thus the DW works as a kind of a ``linear accelerator'' testing
virtual states.Comment: To be published in Proceedings of ECRYS-99, J. de Physique, Coll.,
December 1999, http://ipnweb.in2p3.fr/~lptms/membres/brazov
Density waves and supersolidity in rapidly rotating atomic Fermi gases
We study theoretically the low-temperature phases of a two-component atomic
Fermi gas with attractive s-wave interactions under conditions of rapid
rotation. We find that, in the extreme quantum limit, when all particles occupy
the lowest Landau level, the normal state is unstable to the formation of
"charge" density wave (CDW) order. At lower rotation rates, when many Landau
levels are occupied, we show that the low-temperature phases can be
supersolids, involving both CDW and superconducting order.Comment: 4 pages, 1 figure, uses feynmp.st
Modulated phases of a 1D sharp interface model in a magnetic field
We investigate the ground states of 1D continuum models having short-range
ferromagnetic type interactions and a wide class of competing longer-range
antiferromagnetic type interactions. The model is defined in terms of an energy
functional, which can be thought of as the Hamiltonian of a coarse-grained
microscopic system or as a mesoscopic free energy functional describing various
materials. We prove that the ground state is simple periodic whatever the
prescribed total magnetization might be. Previous studies of this model of
frustrated systems assumed this simple periodicity but, as in many examples in
condensed matter physics, it is neither obvious nor always true that ground
states do not have a more complicated, or even chaotic structure.Comment: 12 pages, 3 figure
Degeneracy and Strong Fluctuation-Induced First-Order Phase Transition in the Dipolar Pyrochlore Antiferromagnet
We show that a continuous set of degenerate critical soft modes strongly
enhances the first-order character of a fluctuation-induced first-order
transition in the pyrochlore dipolar Heisenberg antiferromagnet. Such a
degeneracy seems essential to explain the strong first-order transition
recently observed in Gd(2)Sn(2)O(7). We present some evidence from Monte-Carlo
simulations and a perturbative renormalization group expansion.Comment: 8 pages, 9 figures, new version to appear in PRB, added ref
- …