1,852 research outputs found
Bounday Condition histograms for modulated phases
Boundary conditions strongly affect the results of numerical computations for
finite size inhomogeneous or incommensurate structures. We present a method
which allows to deal with this problem, both for ground state and for critical
properties: it combines fluctuating boundary conditions and specific histogram
techniques. Our approach concerns classical systems possessing a continuous
symmetry as well as quantum systems. In particular, current-current correlation
functions, which probe large scale coherence of the states, can be accurately
evaluated. We illustrate our method on a frustrated two dimensional XY model.Comment: 31 pages, 8 figure
Phase diagram of hole doped two-leg Cu-O ladders
In the weak coupling limit, we establish the phase diagram of a two-leg
ladder with a unit cell containing both Cu and O atoms, as a function of
doping. We use bosonization and design a specific RG procedure to handle the
additional degrees of freedom. Significant differences are found with the
single orbital case; for purely repulsive interactions, a completely massless
quantum critical region is obtained at intermediate carrier concentrations
(well inside the bands) where the ground state consists of an incommensurate
pattern of orbital currents plus a spin density wave (SDW) structure.Comment: 4 pages, 2 figures, accepted to Phys. Rev. B, Rapid Com
Wavefunctions for the Luttinger liquid
Standard bosonization techniques lead to phonon-like excitations in a
Luttinger liquid (LL), reflecting the absence of Landau quasiparticles in these
systems. Yet in addition to the above excitations some LL are known to possess
solitonic states carrying fractional quantum numbers (e.g. the spin 1/2
Heisenberg chain). We have reconsidered the zero modes in the low-energy
spectrum of the gaussian boson LL hamiltonian both for fermionic and bosonic
LL: in the spinless case we find that two elementary excitations carrying
fractional quantum numbers allow to generate all the charge and current excited
states of the LL. We explicitly compute the wavefunctions of these two objects
and show that one of them can be identified with the 1D version of the Laughlin
quasiparticle introduced in the context of the Fractional Quantum Hall effect.
For bosons, the other quasiparticle corresponds to a spinon excitation. The
eigenfunctions of Wen's chiral LL hamiltonian are also derived: they are quite
simply the one dimensional restrictions of the 2D bulk Laughlin wavefunctions.Comment: 5 pages; accepted for publication in EPR B, Rapid Note
Fractional excitations in the Luttinger liquid
We reconsider the spectrum of the Luttinger liquid (LL) usually understood in
terms of phonons (density fluctuations), and within the context of bosonization
we give an alternative representation in terms of fractional states. This
allows to make contact with Bethe Ansatz which predicts similar fractional
states. As an example we study the spinon operator in the absence of spin
rotational invariance and derive it from first principles: we find that it is
not a semion in general; a trial Jastrow wavefunction is also given for that
spinon state. Our construction of the new spectroscopy based on fractional
states leads to several new physical insights: in the low-energy limit, we find
that the continuum of gapless spin chains is due to pairs of
fractional quasiparticle-quasihole states which are the 1D counterpart of the
Laughlin FQHE quasiparticles. The holon operator for the Luttinger liquid with
spin is also derived. In the presence of a magnetic field, spin-charge
separation is not realized any longer in a LL: the holon and the spinon are
then replaced by new fractional states which we are able to describe.Comment: Revised version to appear in Physical Review B. 27 pages, 5 figures.
Expands cond-mat/9905020 (Eur.Phys.Journ.B 9, 573 (1999)
Field-induced local moments around nonmagnetic impurities in metallic cuprates
We consider a defect in a strongly correlated host metal and discuss, within
a slave boson mean field formalism for the model, the formation of an
induced paramagnetic moment which is extended over nearby sites. We study in
particular an impurity in a metallic band, suitable for modelling the optimally
doped cuprates, in a regime where the impurity moment is paramagnetic. The form
of the local susceptibility as a function of temperature and doping is found to
agree well with recent NMR experiments, without including screening processes
leading to the Kondo effect.Comment: 7 pages, submitted to Phys Rev
Coexistence of glassy antiferromagnetism and giant magnetoresistance (GMR) in Fe/Cr multilayer structures
Using temperature-dependent magnetoresistance and magnetization measurements
on Fe/Cr multilayers that exhibit pronounced giant magnetoresistance (GMR), we
have found evidence for the presence of a glassy antiferromagnetic (GAF) phase.
This phase reflects the influence of interlayer exchange coupling (IEC) at low
temperature (T < 140K) and is characterized by a field-independent glassy
transition temperature, Tg, together with irreversible behavior having
logarithmic time dependence below a "de Almeida and Thouless" (AT) critical
field line. At room temperature, where the GMR effect is still robust, IEC
plays only a minor role, and it is the random potential variations acting on
the magnetic domains that are responsible for the antiparallel interlayer
domain alignment.Comment: 5 pages, 4 figure
Spin rotational symmetry breaking by orbital current patterns in two-leg ladders.
We investigate the physical consequences of orbital current patterns (OCP) in
doped two-leg Cu-O Hubbard ladders. The internal symmetry of the pattern, in
the case of the ladder structure, differs slightly from that suggested so far
for cuprates. We focus on this OCP and look for measurable signatures of its
existence. We compute the magnetic field produced by the OCP at each lattice
site, and estimate its value in view of a possible experimental detection.
Using a renormalization group (RG) analysis, we determine the changes that are
caused by the SU(2) spin-rotational symmetry breaking which occurs when the OCP
is present in the ground state phase diagram. The most signifcant one is an
in-plane SDW gap opening in an otherwise critical phase, at intermediate
dopings. We estimate the value of this gap, give an analytic expression for the
correlation functions and examine some of the magnetic properties of this new
phase which can be revealed in measurements. We compute the conductance in the
presence of a single impurity, using an RG analysis. A discussion of the
various sources of SU(2) symmetry breaking underscores the specificity of the
OCP induced effects.Comment: 12 pages, 3 figures, submitted to PR
Large modulation of the Shubnikov-de Haas oscillations by the Rashba interaction at the LaAlO/SrTiO interface
We investigate the 2-dimensional Fermi surface of high-mobility
LaAlO/SrTiO interfaces using Shubnikov-de Haas oscillations. Our
analysis of the oscillation pattern underscores the key role played by the
Rashba spin-orbit interaction brought about by the breaking of inversion
symmetry, as well as the dominant contribution of the heavy /
orbitals on electrical transport. We furthermore bring into light the complex
evolution of the oscillations with the carrier density, which is tuned by the
field effect
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