5,501 research outputs found
Breakdown of Fermi liquid behavior at the (\pi,\pi)=2k_F spin-density wave quantum-critical point: the case of electron-doped cuprates
Many correlated materials display a quantum critical point between a
paramagnetic and a SDW state. The SDW wave vector connects points (hot spots)
on opposite sides of the Fermi surface. The Fermi velocities at these pairs of
points are in general not parallel. Here we consider the case where pairs of
hot spots coalesce, and the wave vector (\pi,\pi) of the SDW connects hot spots
with parallel Fermi velocities. Using the specific example of electron-doped
cuprates, we first show that Kanamori screening and generic features of the
Lindhard function make this case experimentally relevant. The temperature
dependence of the correlation length, the spin susceptibility and the
self-energy at the hot spots are found using the Two-Particle-Self-Consistent
theory and specific numerical examples worked out for parameters characteristic
of the electron-doped cuprates. While the curvature of the Fermi surface at the
hot spots leads to deviations from perfect nesting, the pseudo-nesting
conditions lead to drastic modifications to the temperature dependence of these
physical observables: Neglecting logarithmic corrections, the correlation
length \xi scales like 1/T, i.e. z=1 instead of the naive z=2, the (\pi,\pi)
static spin susceptibility \chi like , and the imaginary part of the
self-energy at the hot spots like . The correction to the Korringa NMR relaxation rate is subdominant. We also consider
this problem at zero temperature, or for frequencies larger than temperature,
using a field-theoretical model of gapless SDW fluctuations interacting with
fermions. The imaginary part of the fermionic self-energy close to the hot
spots scales as . This is less singular than earlier
predictions of the form . The difference arises from the
effects of umklapp terms that were not included in previous studies.Comment: 23 pages, 12 figures; (v2) minor changes; (v3) Final published
versio
Spiral Magnets as Gapless Mott Insulators
In the large limit, the ground state of the half-filled, nearest-neighbor
Hubbard model on the triangular lattice is the three-sublattice
antiferromagnet. In sharp contrast with the square-lattice case, where
transverse spin-waves and charge excitations remain decoupled to all orders in
, it is shown that beyond leading order in the three Goldstone modes
on the triangular lattice are a linear combination of spin and charge. This
leads to non-vanishing conductivity at any finite frequency, even though the
magnet remains insulating at zero frequency. More generally, non-collinear spin
order should lead to such gapless insulating behavior.Comment: 10 pages, REVTEX 3.0, 3 uuencoded postscript figures, CRPS-94-0
Spin susceptibility of interacting electrons in one dimension: Luttinger liquid and lattice effects
The temperature-dependent uniform magnetic susceptibility of interacting
electrons in one dimension is calculated using several methods. At low
temperature, the renormalization group reaveals that the Luttinger liquid spin
susceptibility approaches zero temperature with an infinite slope
in striking contrast with the Fermi liquid result and with the behavior of the
compressibility in the absence of umklapp scattering. This effect comes from
the leading marginally irrelevant operator, in analogy with the Heisenberg spin
1/2 antiferromagnetic chain. Comparisons with Monte Carlo simulations at higher
temperature reveal that non-logarithmic terms are important in that regime.
These contributions are evaluated from an effective interaction that includes
the same set of diagrams as those that give the leading logarithmic terms in
the renormalization group approach. Comments on the third law of thermodynamics
as well as reasons for the failure of approaches that work in higher dimensions
are given.Comment: 21 pages, latex including 5 eps figure
Breakup of the Fermi surface near the Mott transition in low-dimensional systems
We investigate the Mott transition in weakly-coupled one-dimensional (1d)
fermionic chains. Using a generalization of Dynamic Mean Field Theory, we show
that the Mott gap is suppressed at some critical hopping . The
transition from the 1d insulator to a 2d metal proceeds through an intermediate
phase where the Fermi surface is broken into electron and hole pockets. The
quasiparticle spectral weight is strongly anisotropic along the Fermi surface,
both in the intermediate and metallic phases. We argue that such pockets would
look like `arcs' in photoemission experiments.Comment: REVTeX 4, 5 pages, 4 EPS figures. References added; problem with
figure 4 fixed; typos correcte
Superintegrability of the Tremblay-Turbiner-Winternitz quantum Hamiltonians on a plane for odd
In a recent FTC by Tremblay {\sl et al} (2009 {\sl J. Phys. A: Math. Theor.}
{\bf 42} 205206), it has been conjectured that for any integer value of ,
some novel exactly solvable and integrable quantum Hamiltonian on a plane
is superintegrable and that the additional integral of motion is a th-order
differential operator . Here we demonstrate the conjecture for the
infinite family of Hamiltonians with odd , whose first member
corresponds to the three-body Calogero-Marchioro-Wolfes model after elimination
of the centre-of-mass motion. Our approach is based on the construction of some
-extended and invariant Hamiltonian \chh_k, which can be interpreted
as a modified boson oscillator Hamiltonian. The latter is then shown to possess
a -invariant integral of motion \cyy_{2k}, from which can be
obtained by projection in the identity representation space.Comment: 14 pages, no figure; change of title + important addition to sect. 4
+ 2 more references + minor modifications; accepted by JPA as an FT
Third order superintegrable systems separating in polar coordinates
A complete classification is presented of quantum and classical
superintegrable systems in that allow the separation of variables in
polar coordinates and admit an additional integral of motion of order three in
the momentum. New quantum superintegrable systems are discovered for which the
potential is expressed in terms of the sixth Painlev\'e transcendent or in
terms of the Weierstrass elliptic function
- …