100,981 research outputs found
Quantum interference in nested d-wave superconductors: a real-space perspective
We study the local density of states around potential scatterers in d-wave
superconductors, and show that quantum interference between impurity states is
not negligible for experimentally relevant impurity concentrations. The two
impurity model is used as a paradigm to understand these effects analytically
and in interpreting numerical solutions of the Bogoliubov-de Gennes equations
on fully disordered systems. We focus primarily on the globally particle-hole
symmetric model which has been the subject of considerable controversy, and
give evidence that a zero-energy delta function exists in the DOS. The
anomalous spectral weight at zero energy is seen to arise from resonant
impurity states belonging to a particular sublattice, exactly as in the
2-impurity version of this model. We discuss the implications of these findings
for realistic models of the cuprates.Comment: 12 pages, 10 figs, submitted to Phys. Rev.
Two impurities in a d-wave superconductor:local density of states
We study the problem of two local potential scatterers in a d-wave
superconductor, and show how quasiparticle bound state wave functions
interfere. Each single-impurity electron and hole resonance energy is in
general split in the presence of a second impurity into two, corresponding to
one even parity and one odd parity state. We calculate the local density of
states (LDOS), and argue that scanning tunneling microscopy (STM) measurements
should be capable of extracting information about the Green's function in the
pure system by a systematic study of 2-impurity configurations. In some
configurations highly localized, long-lived states are predicted. We discuss
the effects of realistic band structures, and how 2-impurity STM measurements
could help distinguish between current explanations of LDOS impurity spectra in
the BSCCO-2212 system.Comment: 16 pages,21 figure,New Version to be Published on P.R.
Formation and Stability of Cellular Carbon Foam Structures:An {\em Ab Initio} Study
We use ab initio density functional calculations to study the formation and
structural as well as thermal stability of cellular foam-like carbon
nanostructures. These systems with a mixed bonding character may be
viewed as bundles of carbon nanotubes fused to a rigid contiguous 3D honeycomb
structure that can be compressed more easily by reducing the symmetry of the
honeycombs. The foam may accommodate the same type of defects as graphene, and
its surface may be be stabilized by terminating caps. We postulate that the
foam may form under non-equilibrium conditions near grain boundaries of a
carbon-saturated metal surface
Topography of Spin Liquids on a Triangular Lattice
Spin systems with frustrated anisotropic interactions are of significant
interest due to possible exotic ground states. We have explored their phase
diagram on a nearest-neighbor triangular lattice using the density-matrix
renormalization group and mapped out the topography of the region that can
harbor a spin liquid. We find that this spin-liquid phase is continuously
connected to a previously discovered spin-liquid phase of the isotropic
model. The two limits show nearly identical spin correlations,
making the case that their respective spin liquids are isomorphic to each
other.Comment: Accepted to PRL; 5 p., 11+ p. supplemental; main text is longer than
the accepted versio
Disorder-Induced Mimicry of a Spin Liquid in YbMgGaO
We suggest that a randomization of the pseudo-dipolar interaction in the
spin-orbit-generated low-energy Hamiltonian of YbMgGaO due to an
inhomogeneous charge environment from a natural mixing of Mg and
Ga can give rise to orientational spin disorder and mimic a
spin-liquid-like state. In the absence of such quenched disorder, and
density matrix renormalization group calculations both show robust ordered
states for the physically relevant phases of the model. Our scenario is
consistent with the available experimental data and further experiments are
proposed to support it.Comment: 5+ main text, 7+ supplemental, text asymptotically close to PR
Effects of Minijets on Hadronic Spectra and Azimuthal Harmonics in Au-Au Collisions at 200 GeV
The production of hadrons in heavy-ion collisions at RHIC in the low
transverse-momentum () region is investigated in the recombination model
with emphasis on the effects of minijets on the azimuthal anisotropy. Since the
study is mainly on the hadronization of partons at late time, the fluid picture
is not used to trace the evolution of the system. The inclusive distributions
at low are determined as the recombination products of thermal partons.
The dependencies of both pion and proton have a common exponential factor
apart from other dissimilar kinematic and resonance factors, because they are
inherited from the same pool of thermal partons. Instead of the usual
description based on hydrodynamics, the azimuthal anisotropy of the produced
hadrons is explained as the consequence of the effects of minijets, either
indirectly through the recombination of enhanced thermal partons in the
vicinity of the trajectories of the semihard partons, or directly through
thermal-shower recombination. Although our investigation is focussed on the
single-particle distribution at midrapidity, we give reasons why a component in
that distribution can be identified with the ridge, which together with the
second harmonic is due to the semihard partons created near the medium
surface that lead to calculable anisotropy in . It is shown that the
higher azimuthal harmonics, , can also be well reproduced without
reference to flow. The and centrality dependencies of the higher
harmonics are prescribed by the interplay between TT and TS recombination
components. The implication of the success of this drastic departure from the
conventional approach is discussed.Comment: 28 pages and 8 figures, more discussions and references adde
Kawasaki-type Dynamics: Diffusion in the kinetic Gaussian model
In this article, we retain the basic idea and at the same time generalize
Kawasaki's dynamics, spin-pair exchange mechanism, to spin-pair redistribution
mechanism, and present a normalized redistribution probability. This serves to
unite various order-parameter-conserved processes in microscopic, place them
under the control of a universal mechanism and provide the basis for further
treatment. As an example of the applications, we treated the kinetic Gaussian
model and obtained exact diffusion equation. We observed critical slowing down
near the critical point and found that, the critical dynamic exponent z=1/nu=2
is independent of space dimensionality and the assumed mechanism, whether
Glauber-type or Kawasaki-type.Comment: accepted for publication in PR
Continuous quantum phase transition in a Kondo lattice model
We study the magnetic quantum phase transition in an anisotropic Kondo
lattice model. The dynamical competition between the RKKY and Kondo
interactions is treated using an extended dynamic mean field theory (EDMFT)
appropriate for both the antiferromagnetic and paramagnetic phases. A quantum
Monte Carlo approach is used, which is able to reach very low temperatures, of
the order of 1% of the bare Kondo scale. We find that the finite-temperature
magnetic transition, which occurs for sufficiently large RKKY interactions, is
first order. The extrapolated zero-temperature magnetic transition, on the
other hand, is continuous and locally critical.Comment: 4 pages, 4 figures; updated, to appear in PR
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