81 research outputs found
Ultrahigh magnetic field spectroscopy reveals the band structure of the 3D topological insulator BiSe
We have investigated the band structure at the point of the
three-dimensional (3D) topological insulator BiSe using
magneto-spectroscopy over a wide range of energies (\,eV) and in
ultrahigh magnetic fields up to 150\,T. At such high energies (\,eV) the
parabolic approximation for the massive Dirac fermions breaks down and the
Landau level dispersion becomes nonlinear. At even higher energies around 0.99
and 1.6 eV, new additional strong absorptions are observed with a temperature
and magnetic-field dependence which suggest that they originate from higher
band gaps. Spin orbit splittings for the further lying conduction and valence
bands are found to be 0.196 and 0.264 eV
Status of the BMV experiment
In this contribution we present the status of the BMV experiment whose goal
is to measure the vacuum magnetic birefringence
High Field magnetospectroscopy to probe the 1.4eV Ni color center in diamond
A magneto-optical study of the 1.4 eV Ni color center in boron-free synthetic
diamond, grown at high pressure and high temperature, has been performed in
magnetic fields up to 56 T. The data is interpreted using the effective spin
Hamiltonian of Nazar\'e, Nevers and Davies [Phys. Rev. B 43, 14196 (1991)] for
interstitial Ni with the electronic configuration and effective
spin . Our results unequivocally demonstrate the trigonal symmetry of
the defect which preferentially aligns along the [111] growth direction on the
(111) face, but reveal the shortcomings of the crystal field model for this
particular defect.Comment: 12 pages, 13 figures, submitted to PR
Magnetic Brightening of Carbon Nanotube Photoluminescence through Symmetry Breaking
Often a modification of microscopic symmetry in a system can result in a
dramatic change in its macroscopic properties. Here we report that symmetry
breaking by a tube-threading magnetic field can drastically increase the
photoluminescence quantum yield of semiconducting single-walled carbon
nanotubes, by as much as a factor of six, at low temperatures. To explain this
striking connection between seemingly unrelated properties, we have developed a
comprehensive theoretical model based on magnetic-field-dependent
one-dimensional exciton band structure and the interplay of strong Coulomb
interactions and the Aharonov-Bohm effect. This conclusively explains our data
as the first experimental observation of dark excitons 5-10 meV below the
bright excitons in single-walled carbon nanotubes. We predict that this quantum
yield increase can be made much larger in disorder-free samples
Transport and magnetic properties of LT annealed Ga1-xMnxAs
We present the results of low temperature (LT) annealing studies of
Ga1-xMnxAs epilayers grown by low temperature molecular beam epitaxy in a wide
range of Mn concentrations (0.01<x<0.084). Transport measurements in low and
high magnetic fields as well as SQUID measurements were performed on a wide
range of samples, serving to establish optimal conditions of annealing. Optimal
annealing procedure succeeded in the Curie temperatures higher than 110K. The
highest value of Curie temperature estimated from the maximum in the
temperature dependence of zero-field resistivity (Tr) was 127K. It is generally
observed that annealing leads to large changes in the magnetic and transport
properties of GaMnAs in the very narrow range of annealing temperature close to
the growth temperature.Comment: XXXI International School on the Physics of Semiconducting Compounds
Jaszowiec 2002, will be published in Acta Physica Polonica
Alignment Dynamics of Single-Walled Carbon Nanotubes in Pulsed Ultrahigh Magnetic Fields
We have measured the dynamic alignment properties of single-walled carbon
nanotube (SWNT) suspensions in pulsed high magnetic fields through linear
dichroism spectroscopy. Millisecond-duration pulsed high magnetic fields up to
56 T as well as microsecond-duration pulsed ultrahigh magnetic fields up to 166
T were used. Due to their anisotropic magnetic properties, SWNTs align in an
applied magnetic field, and because of their anisotropic optical properties,
aligned SWNTs show linear dichroism. The characteristics of their overall
alignment depend on several factors, including the viscosity and temperature of
the suspending solvent, the degree of anisotropy of nanotube magnetic
susceptibilities, the nanotube length distribution, the degree of nanotube
bundling, and the strength and duration of the applied magnetic field. In order
to explain our data, we have developed a theoretical model based on the
Smoluchowski equation for rigid rods that accurately reproduces the salient
features of the experimental data.Comment: 20 pages, 6 figure
Tuning the magnetic ground state of a novel tetranuclear Nickel(II) molecular complex by high magnetic fields
Electron spin resonance and magnetization data in magnetic fields up to 55 T
of a novel multicenter paramagnetic molecular complex [L_2Ni_4(N_3)(O_2C
Ada)_4](Cl O_4) are reported. In this compound, four Ni centers each having a
spin S = 1 are coupled in a single molecule via bridging ligands (including a
\mu_4-azide) which provide paths for magnetic exchange. Analysis of the
frequency and temperature dependence of the ESR signals yields the relevant
parameters of the spin Hamiltonian, in particular the single ion anisotropy gap
and the g factor, which enables the calculation of the complex energy spectrum
of the spin states in a magnetic field. The experimental results give
compelling evidence for tuning the ground state of the molecule by magnetic
field from a nonmagnetic state at small fields to a magnetic one in strong
fields owing to the spin level crossing at a field of ~25 T.Comment: revised version, accepted for publication in Physical Review
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