181 research outputs found
Spin susceptibility and polarization field in a dilute two-dimensional electron system in (111) silicon
We find that the polarization field, B_chi, obtained by scaling the
weak-parallel-field magnetoresistance at different electron densities in a
dilute two-dimensional electron system in (111) silicon, corresponds to the
spin susceptibility that grows strongly at low densities. The polarization
field, B_sat, determined by resistance saturation, turns out to deviate to
lower values than B_chi with increasing electron density, which can be
explained by filling of the upper electron subbands in the fully spin-polarized
regime
Electron-hole coexistence in disordered graphene probed by high-field magneto-transport
We report on magneto-transport measurement in disordered graphene under
pulsed magnetic field of up to 57T. For large electron or hole doping, the
system displays the expected anomalous Integer Quantum Hall Effect (IQHE)
specific to graphene up to filling factor . In the close vicinity of the
charge neutrality point, the system breaks up into co-existing puddles of holes
and electrons, leading to a vanishing Hall and finite longitudinal resistance
with no hint of divergence at very high magnetic field. Large resistance
fluctuations are observed near the Dirac point. They are interpreted as the the
natural consequence of the presence of electron and hole puddles. The magnetic
field at which the amplitude of the fluctuations are the largest is directly
linked to the mean size of the puddles
Magnetic Anisotropy of Co2+ as Signature of Intrinsic Ferromagnetism in ZnO:Co
We report on the magnetic properties of thoroughly characterized Zn1-xCoxO
epitaxial thin films, with low Co concentration, x=0.003-0.005. Magnetic and
EPR measurements, combined with crystal field theory, reveal that isolated Co2+
ions in ZnO possess a strong single ion anisotropy which leads to an "easy
plane" ferromagnetic state when the ferromagnetic Co-Co interaction is
considered. We suggest that the peculiarities of the magnetization process of
this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co
materials.Comment: 4 pages, 4 figure
Integer Quantum Hall Effect in Trilayer Graphene
The Integer Quantum Hall Effect (IQHE) is a distinctive phase of
two-dimensional electronic systems subjected to a perpendicular magnetic field.
Thus far, the IQHE has been observed in semiconductor heterostructures and in
mono- and bi-layer graphene. Here we report on the IQHE in a new system:
trilayer graphene. Experimental data are compared with self-consistent Hartree
calculations of the Landau levels for the gated trilayer. The plateau structure
in the Hall resistivity determines the stacking order (ABA versus ABC). We find
that the IQHE in ABC trilayer graphene is similar to that in the monolayer,
except for the absence of a plateau at filling factor v=2. At very low filling
factor, the Hall resistance vanishes due to the presence of mixed electron and
hole carriers induced by disorder.Comment: 5 pages, 4 figure
Cyclotron resonance of extremely conductive 2D holes in high Ge content strained heterostructures
Cyclotron resonance has been observed in steady and pulsed magnetic fields from high conductivity holes in Ge quantum wells. The resonance positions, splittings and linewidths are compared to calculations of the hole Landau levels
Temperature-dependent magnetospectroscopy of HgTe quantum wells
We report on magnetospectroscopy of HgTe quantum wells in magnetic fields up
to 45 T in temperature range from 4.2 K up to 185 K. We observe intra- and
inter-band transitions from zero-mode Landau levels, which split from the
bottom conduction and upper valence subbands, and merge under the applied
magnetic field. To describe experimental results, realistic
temperature-dependent calculations of Landau levels have been performed. We
show that although our samples are topological insulators at low temperatures
only, the signature of such phase persists in optical transitions at high
temperatures and high magnetic fields. Our results demonstrate that
temperature-dependent magnetospectroscopy is a powerful tool to discriminate
trivial and topological insulator phases in HgTe quantum wells
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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