21,903 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.
Observation of the Purcell effect in high-index-contrast micropillar
We have fabricated pillar microcavity samples with Bragg mirrors consisting
of alternate layers of GaAs and Aluminium Oxide. Compared to the more widely
studied GaAs/AlAs micropillars these mirrors can achieve higher reflectivities
with fewer layer repeats and reduce the mode volume. We have studied a number
of samples containing a low density of InGaAs/GaAs self assembled quantum dots
in a cavity and here report observation of a three fold enhancement in the
radiative lifetime of a quantum dot exciton state due to the Purcell effect
Oxide-apertured microcavity single-photon emitting diode
We have developed a microcavity single-photon source based on a single
quantum dot within a planar cavity in which wet-oxidation of a high-aluminium
content layer provides lateral confinement of both the photonic mode and the
injection current. Lateral confinement of the optical mode in optically pumped
structures produces a strong enhancement of the radiative decay rate. Using
microcavity structures with doped contact layers, we demonstrate a
single-photon emitting diode where current may be injected into a single dot
Dark Solitons in Discrete Lattices: Saturable versus Cubic Nonlinearities
In the present work, we study dark solitons in dynamical lattices with the
saturable nonlinearity and compare them with those in lattices with the cubic
nonlinearity. This comparison has become especially relevant in light of recent
experimental developments in the former context. The stability properties of
the fundamental waves, for both on-site and inter-site modes, are examined
analytically and corroborated by numerical results. Furthermore, their
dynamical evolution when they are found to be unstable is obtained through
appropriately crafted numerical experiments.Comment: 15 pages, 5 figure
On the precision of chiral-dispersive calculations of scattering
We calculate the combination (the Olsson sum rule)
and the scattering lengths and effective ranges , and ,
dispersively (with the Froissart--Gribov representation) using, at
low energy, the phase shifts for scattering obtained by Colangelo,
Gasser and Leutwyler (CGL) from the Roy equations and chiral perturbation
theory, plus experiment and Regge behaviour at high energy, or directly, using
the CGL parameters for s and s. We find mismatch, both among the CGL
phases themselves and with the results obtained from the pion form factor. This
reaches the level of several (2 to 5) standard deviations, and is essentially
independent of the details of the intermediate energy region ( GeV) and, in some cases, of the high energy behaviour assumed. We discuss
possible reasons for this mismatch, in particular in connection with an
alternate set of phase shifts.Comment: Version to appear in Phys. Rev. D. Graphs and sum rule added. Plain
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