5,659 research outputs found
Large Magnetic Susceptibility Anisotropy of Metallic Carbon Nanotubes
Through magnetic linear dichroism spectroscopy, the magnetic susceptibility
anisotropy of metallic single-walled carbon nanotubes has been extracted and
found to be 2-4 times greater than values for semiconducting single-walled
carbon nanotubes. This large anisotropy is consistent with our calculations and
can be understood in terms of large orbital paramagnetism of electrons in
metallic nanotubes arising from the Aharonov-Bohm-phase-induced gap opening in
a parallel field. We also compare our values with previous work for
semiconducting nanotubes, which confirm a break from the prediction that the
magnetic susceptibility anisotropy increases linearly with the diameter.Comment: 4 pages, 4 figure
The ATLAS trigger menu for early data-taking
The ATLAS trigger system is based on three levels of event selection that
select the physics of interest from an initial bunch-crossing rate of 40 MHz.
During nominal LHC operations at a luminosity of 10^34 cm^-2 s^-1, decisions
must be taken every 25 ns with each bunch crossing containing about 23
interactions. The selections in the three trigger levels must provide
sufficient rejection to reduce the rate down to 200 Hz, compatible with the
offline computing power and storage capacity. The LHC is expected to begin
operations in summer 2008 with a peak luminosity of 10^31 cm^-2 s^-1 with far
fewer bunches than nominal running, but quickly ramp up to higher luminosities.
Hence, we need to deploy trigger selections that can adapt to the changing beam
conditions preserving the interesting physics and detector requirements that
may vary with these conditions.
We present the status of the preparation of the trigger menu for the early
data-taking showing how we plan to deploy the trigger system from the first
collision to the nominal luminosity. We also show expected rates and physics
performance obtained from simulated data.Comment: Poster presentation at the Hadron Collider Physics Symposium
(HCP2008), Galena, Illinois, USA, May 27-31, 2008; 5 pages, LaTeX, 2 eps
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Magneto-reflection spectroscopy of monolayer transition-metal dichalcogenide semiconductors in pulsed magnetic fields
We describe recent experimental efforts to perform polarization-resolved
optical spectroscopy of monolayer transition-metal dichalcogenide
semiconductors in very large pulsed magnetic fields to 65 tesla. The
experimental setup and technical challenges are discussed in detail, and
temperature-dependent magneto-reflection spectra from atomically thin tungsten
disulphide (WS) are presented. The data clearly reveal not only the valley
Zeeman effect in these 2D semiconductors, but also the small quadratic exciton
diamagnetic shift from which the very small exciton size can be directly
inferred. Finally, we present model calculations that demonstrate how the
measured diamagnetic shifts can be used to constrain estimates of the exciton
binding energy in this new family of monolayer semiconductors.Comment: PCSI-43 conference (Jan. 2016; Palm Springs, CA
Exciton Diamagnetic Shifts and Valley Zeeman Effects in Monolayer WS and MoS to 65 Tesla
We report circularly-polarized optical reflection spectroscopy of monolayer
WS and MoS at low temperatures (4~K) and in high magnetic fields to
65~T. Both the A and the B exciton transitions exhibit a clear and very similar
Zeeman splitting of approximately 230~eV/T (), providing
the first measurements of the valley Zeeman effect and associated -factors
in monolayer transition-metal disulphides. These results complement and are
compared with recent low-field photoluminescence measurements of valley
degeneracy breaking in the monolayer diselenides MoSe and WSe. Further,
the very large magnetic fields used in our studies allows us to observe the
small quadratic diamagnetic shifts of the A and B excitons in monolayer WS
(0.32 and 0.11~eV/T, respectively), from which we calculate exciton
radii of 1.53~nm and 1.16~nm. When analyzed within a model of non-local
dielectric screening in monolayer semiconductors, these diamagnetic shifts also
constrain and provide estimates of the exciton binding energies (410~meV and
470~meV for the A and B excitons, respectively), further highlighting the
utility of high magnetic fields for understanding new 2D materials.Comment: 9 pages, 5 figure
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