230 research outputs found
STM imaging of a bound state along a step on the surface of the topological insulator BiTe
Detailed study of the LDOS associated with the surface-state-band near a
step-edge of the strong topological-insulator Bi2Te3, reveal a one-dimensional
bound state that runs parallel to the stepedge and is bound to it at some
characteristic distance. This bound state is clearly observed in the bulk gap
region, while it becomes entangled with the oscillations of the warped surface
band at high energy, and with the valence band states near the Dirac point.
Using the full effective Hamiltonian proposed by Zhang et al., we obtain a
closed formula for this bound state that fits the data and provide further
insight into the general topological properties of the electronic structure of
the surface band near strong structural defects.Comment: 5 pages, 4 figure
Improved constraints on non-Newtonian forces at 10 microns
Several recent theories suggest that light moduli or particles in "large"
extra dimensions could mediate macroscopic forces exceeding gravitational
strength at length scales below a millimeter. Such new forces can be
parameterized as a Yukawa-type correction to the Newtonian potential of
strength relative to gravity and range . To extend the search
for such new physics we have improved our apparatus utilizing cryogenic
micro-cantilevers capable of measuring attonewton forces, which now includes a
switchable magnetic force for calibration. Our most recent experimental
constraints on Yukawa-type deviations from Newtonian gravity are more than
three times as stringent as our previously published results, and represent the
best bound in the range of 5 - 15 microns, with a 95 percent confidence
exclusion of forces with at = 10 microns.Comment: 12 pages, 9 figures, accepted for publication in PRD. Minor changes,
replaced and corrected Figs 4,5,
Possible field-tuned SIT in high-Tc superconductors: implications for pairing at high magnetic fields
The behavior of some high temperature superconductors (HTSC) such as and , at very high
magnetic field, is similar to that of thin films of amorphous InOx near the
magnetic field-tuned superconductor-insulator transition. Analyzing the InOx
data at high fields in terms of persisting local pairing amplitude, we argue by
analogy that local pairing amplitude also persists well into the dissipative
state of the HTSCs, the regime commonly denoted as the "normal state" in very
high magnetic field experiments.Comment: Revised figures and reference
Inferring effective interactions from the local density of states: application to STM data from BiSrCaCuO
While the influence of impurities on the local density of states (LDOS) in a
metal is notoriously non-local due to interference effects, low order moments
of the LDOS in general can be shown to depend only on the local structure of
the Hamiltonian. Specifically, we show that an analysis of the spatial
variations of these moments permits one to ``work backwards'' from scanning
tunneling microscopy (STM) data to infer the local structure of the underlying
effective Hamiltonian. Applying this analysis to STM data from the high
temperature superconductor, BiSrCaCuO, we find that
the variations of the electro-chemical potential are remarkably small (i.e.,
the disorder is, in a sense, weak) but that there are large variations in the
local magnitude of the d-wave gap parameter.Comment: 7 pages, 7 figure
Inhomogeneity Induces Resonance Coherence Peaks in Superconducting BSCCO
In this paper we analyze, using scanning tunneling spectroscopy, the density
of electronic states in nearly optimally doped BSCCO in zero field. Focusing on
the superconducting gap, we find patches of what appear to be two different
phases in a background of some average gap, one with a relatively small gap and
sharp large coherence peaks and one characterized by a large gap with broad
weak coherence peaks. We compare these spectra with calculations of the local
density of states for a simple phenomenological model in which a 2 xi_0 * 2
xi_0 patch with an enhanced or supressed d-wave gap amplitude is embedded in a
region with a uniform average d-wave gap.Comment: 4 pages, 3 figure
STM imaging of impurity resonances on BiSe
In this paper we present detailed study of the density of states near defects
in BiSe. In particular, we present data on the commonly found
triangular defects in this system. While we do not find any measurable
quasiparticle scattering interference effects, we do find localized resonances,
which can be well fitted by theory once the potential is taken to be extended
to properly account for the observed defects. The data together with the fits
confirm that while the local density of states around the Dirac point of the
electronic spectrum at the surface is significantly disrupted near the impurity
by the creation of low-energy resonance state, the Dirac point is not locally
destroyed. We discuss our results in terms of the expected protected surface
state of topological insulators.Comment: 5 pages, 6 figure
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