47 research outputs found
Interplay between the edge-state magnetism and long-range Coulomb interaction in zigzag graphene nanoribbons: quantum Monte Carlo study
We perform projective quantum Monte Carlo simulations of zigzag graphene
nanoribbons within a realistic model with long-range Coulomb interactions.
Increasing the relative strength of nonlocal interactions with respect to the
on-site repulsion does not generate a phase transition but has a number of
nontrivial effects. At the single-particle level we observe a marked
enhancement of the Fermi velocity at the Dirac points. At the two-particle
level, spin- and charge-density-wave fluctuations compete. As a consequence,
the edge magnetic moment is reduced but the edge dispersion relation increases
in the sense that the single-particle gap at momentum
grows. We attribute this to nonlocal charge fluctuations which assist the spin
fluctuations to generate the aforementioned gap. In contrast, the net result of
the interaction-induced renormalization of different energy scales is a
constant spin-wave velocity of the edge modes. However, since the particle-hole
continuum is shifted to higher energies---due to the renormalization of the
Fermi velocity---Landau damping is reduced. As a result, a roughly linear
spin-wave-like mode at the edge spreads out through a larger part of the
Brillouin zone.Comment: 11 pages, 11 figures, comment about doped nanoribbon
Melting of stripe phases and its signature in the single-particle spectral function
Motivated by the recent experimental data [Phys. Rev. B 79, 100502 (2009)]
indicating the existence of a pure stripe charge order over unprecedently wide
temperature range in La_{1.8-x}Eu_{0.2}Sr_xCuO_4, we investigate the
temperature-induced melting of the metallic stripe phase. In spite of taking
into account local dynamic correlations within a real-space dynamical
mean-field theory of the Hubbard model, we observe a mean-field like melting of
the stripe order irrespective of the choice of the next-nearest neighbor
hopping. The temperature dependence of the single-particle spectral function
shows the stripe induced formation of a flat band around the antinodal points
accompanied by the opening a gap in the nodal direction.Comment: 4 pages, 5 figures, minor changes, added Ref. 1
Emergent Coherent Lattice Behavior in Kondo Nanosystems
How many magnetic moments periodically arranged on a metallic surface are
needed to generate a coherent Kondo lattice behavior? We investigate this
fundamental issue within the particle-hole symmetric Kondo lattice model using
quantum Monte Carlo simulations. Extra magnetic atoms forming closed shells
around the initial impurity induce a fast splitting of the Kondo resonance at
the inner shells which signals the formation of composite heavy-fermion bands.
The onset of the hybridization gap matches well the enhancement of
antiferromagnetic spin correlations in the plane perpendicular to the applied
magnetic field, a genuine feature of the coherent Kondo lattice. In contrast,
the outermost shell remains dominated by a local Kondo physics with spectral
features resembling the single-impurity behavior.Comment: 4+ pages plus supplemental material; published versio
d-wave Superconductivity, Orbital Magnetism, and Unidirectional Charge Order in the t-J Model
Recent scanning tunneling microscopy in the superconducting regime of two
different cuprate families has revealed unidirectional bond-centered modulation
in the local electronic density of states. Motivated by this result we
investigate the emergence of modulated d-wave superconductivity coexisting with
charge domains that form along one of the crystal axes. While detailed stripe
profiles depend on the used form of the Gutzwiller factors, the tendency
towards a valence bond crystal remain robust. We also find closely related
stripe phase originating from the staggered flux phase, a candidate for the
pseudogap phase of lightly doped cuprates.Comment: 8 pages, 4 figure
Mechanism of the reorientation of stripes in the cuprates
Using the mean field theory in the slave-boson approach we analyzed the
electron correlation effects in the stripe phases. One finds that a finite
next-nearest neighbor hopping plays an important role in the low doping
regime, where it controls the crossover from the filled diagonal to half-filled
vertical/horizontal stripes at doping .Comment: 2 pages, 1 figur
Stability of RVB hole stripes in high-temperature superconductors
Indications of density-wave states in underdoped cuprates, coming from recent
STM (scanning tunneling microscopy) and Hall-resistance measurements, have
raised new concerns whether stripes could be stabilized in the superconducting
phase of cuprate materials, even in the absence of antiferromagnetism. Here, we
investigate this issue using state-of-the-art quantum Monte Carlo calculations
of a model. In particular we consider the stability of unidirectional
hole domains in a modulated superconducting background, by taking into account
the effect of tetragonal-lattice distortions, next-nearest neighbor hopping and
long-range Coulomb repulsion.Comment: 8 pages, 9 figures. Enlarged versio
Spin-rotationally symmetric domain flux phases in underdoped cuprates
We propose a new form of inhomogeneous phases consisting of out-of-phase
staggered flux domains separated by diagonal charged domain walls centered on
bonds or on sites. Remarkably, such domain flux phases are spin-rotationally
symmetric and exhibit cone-like quasiparticle dispersion as well as
incommensurate order of orbital currents. Such features are consistent with the
pseudogap behavior and the diagonal stripes observed experimentally in lightly
doped cuprates. A renormalized mean field theory shows that such solutions are
competitive candidates within the -- model.Comment: 6 pages, 3 figure