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Bulk Band Gap and Surface State Conduction Observed in Voltage-Tuned Crystals of the Topological Insulator BiSe
We report a transport study of exfoliated few monolayer crystals of
topological insulator BiSe in an electric field effect (EFE) geometry.
By doping the bulk crystals with Ca, we are able to fabricate devices with
sufficiently low bulk carrier density to change the sign of the Hall density
with the gate voltage . We find that the temperature and magnetic
field dependent transport properties in the vicinity of this can be
explained by a bulk channel with activation gap of approximately 50 meV and a
relatively high mobility metallic channel that dominates at low . The
conductance (approximately 2 7), weak anti-localization, and
metallic resistance-temperature profile of the latter lead us to identify it
with the protected surface state. The relative smallness of the observed gap
implies limitations for EFE topological insulator devices at room temperature.Comment: 4 pages, 4 figures. In new version, panels have been removed from
Figures 1, 2, and 4 to improve clarity. Additional data included in Figure 4.
Introduction and discussion revised and expande
Unusual Nernst effect suggestive of time-reversal violation in the striped cuprate LaBaCuO
The striped cuprate LaBaCuO ( undergoes several
transitions below the charge-ordering temperature = 54 K. From Nernst
experiments, we find that, below , there exists a large, anomalous
Nernst signal that is symmetric in field , and remains
finite as . The time-reversal violating signal suggests that, below
, vortices of one sign are spontaneously created to relieve interlayer
phase frustration.Comment: 5 pages, 4 figure
The Nernst effect in high- superconductors
The observation of a large Nernst signal in an extended region above
the critical temperature in hole-doped cuprates provides evidence that
vortex excitations survive above . The results support the scenario that
superfluidity vanishes because long-range phase coherence is destroyed by
thermally-created vortices (in zero field), and that the pair condensate
extends high into the pseudogap state in the underdoped (UD) regime. We present
a series of measurements to high fields which provide strong evidence for
this phase-disordering scenario.Comment: 21 pages, 28 figure
Reply to ``Comment on `Insulating Behavior of -DNA on the Micron Scale' "
In our experiment, we found that the resistance of vacuum-dried -DNA
exceeds at 295 K. Bechhoefer and Sen have raised a number of
objections to our conclusion. We provide counter arguments to support our
original conclusion.Comment: 1 page reply to comment, 1 figur
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