289 research outputs found
Observation of anisotropic interlayer Raman modes in few-layer ReS2
ReS has recently emerged as a new member in the rapidly growing family of
two-dimensional materials. Unlike MoS or WSe, the optical and
electrical properties of ReS are not isotropic due to the reduced symmetry
of the crystal. Here, we present layer-dependent Raman measurements of ReS
samples ranging from monolayers to ten layers in the ultralow frequency regime.
We observe layer breathing and shear modes which allow for easy assignment of
the number of layers. Polarization-dependent measurements give further insight
into the crystal structure and reveal an energetic shift of the shear mode
which stems from the in-plane anisotropy of the shear modulus in this material
Resonant spin amplification of hole spin dynamics in two‐dimensional hole systems: experiment and simulation
Spins in semiconductor structures may allow for the realization of scalable quantum bit arrays, an essential
component for quantum computation schemes. Specifically, hole spins may be more suited for this purpose than electron
spins, due to their strongly reduced interaction with lattice nuclei, which limits spin coherence for electrons in quantum dots.
Here, we present resonant spin amplification (RSA) measurements, performed on a p-modulation doped GaAs-based quantum
well at temperatures below 500 mK. The RSA traces have a peculiar, butterfly-like shape, which stems from the initialization
of a resident hole spin polarization by optical orientation. The combined dynamics of the optically oriented electron and hole
spins are well-described by a rate equation model, and by comparison of experiment and model, hole spin dephasing times of
more than 70 ns are extracted from the measured data
Controlling hole spin dynamics in two‐dimensional hole systems at low temperatures
With the recent discovery of very long hole spin decoherence times in GaAs/AlGaAs heterostructures of more than 70 ns
in two-dimensional hole systems, using the hole spin as a viable alternative to electron spins in spintronic applications seems
possible. Furthermore, as the hyperfine interaction with the nuclear spins is likely to be the limiting factor for electron spin
lifetimes in zero dimensions, holes with their suppressed Fermi contact hyperfine interaction due to their p-like nature should
be able to show even longer lifetimes than electrons. For spintronic applications, electric-field control of hole spin dynamics
is desirable.
Here, we report on time-resolved Kerr rotation and resonant spin amplification measurements on a two-dimensional hole
system in a p-doped GaAs/AlGaAs heterostructure. Via a semitransparent gate, we tune the charge density within the sample.
We are able to observe a change in the hole g factor, as well as in the hole spin dephasing time at high magnetic fields
Identification of excitons, trions and biexcitons in single-layer WS2
Single-layer WS is a direct-gap semiconductor showing strong excitonic
photoluminescence features in the visible spectral range. Here, we present
temperature-dependent photoluminescence measurements on mechanically exfoliated
single-layer WS, revealing the existence of neutral and charged excitons at
low temperatures as well as at room temperature. By applying a gate voltage, we
can electrically control the ratio of excitons and trions and assert a residual
n-type doping of our samples. At high excitation densities and low
temperatures, an additional peak at energies below the trion dominates the
photoluminescence, which we identify as biexciton emission.Comment: 6 pages, 5 figure
Tailored nano-antennas for directional Raman studies of individual carbon nanotubes
We exploit the near field enhancement of nano-antennas to investigate the
Raman spectra of otherwise not optically detectable carbon nanotubes (CNTs). We
demonstrate that a top-down fabrication approach is particularly promising when
applied to CNTs, owing to the sharp dependence of the scattered intensity on
the angle between incident light polarization and CNT axis. In contrast to tip
enhancement techniques, our method enables us to control the light polarization
in the sample plane, locally amplifying and rotating the incident field and
hence optimizing the Raman signal. Such promising features are confirmed by
numerical simulations presented here. The relative ease of fabrication and
alignment makes this technique suitable for the realization of integrated
devices that combine scanning probe, optical, and transport characterization
Local scale-invariance in ageing phenomena
Many materials quenched into their ordered phase undergo ageing and there
show dynamical scaling. For any given dynamical exponent z, this can be
extended to a new form of local scale-invariance which acts as a dynamical
symmetry. The scaling functions of the two-time correlation and response
functions of ferromagnets with a non-conserved order parameter are determined.
These results are in agreement with analytical and numerical studies of various
models, especially the kinetic Glauber-Ising model in 2 and 3 dimensions.Comment: Invited talk; spring meeting of the german physical society,
Regensburg the 8th of March 2004, 12 pages, style file
Charged Excitons in the Quantum Hall Regime
We review our recent optical experiments on two-dimensional electron systems at temperatures below 1 K and under high magnetic fields. The two-dimensional electron systems are realized in modulation-doped GaAs-AlGaAs single quantum wells. Via gate electrodes the carrier density of the two-dimensional electron systems can be tuned in a quite broad range between about 1×10^{10} cm^{-2} and 2×10^{11} cm^{-2}. In dilute two-dimensional electron systems, at very low electron densities, we observe the formation of negatively charged excitons in photoluminescence experiments. In this contribution we report about the observation of a dark triplet exciton, which is observable at temperatures below 1 K and for electron filling factors <1/3, i.e., in the fractional quantum Hall regime only. In experiments where we have increased the density of the two-dimensional electron systems so that a uniform two-dimensional electron system starts to form, we have found a strong energy anomaly of the charged excitons in the vicinity of filling factor 1/3. This anomaly was found to exist in a very narrow parameter range of the density and temperature, only. We propose a model where we assume that localized charged excitons and a uniform Laughlin liquid coexist. The localized charged exciton in close proximity to the Laughlin liquid leads to the creation of a fractionally-charged quasihole in the liquid, which can account for the experimentally observed anomaly
Fatal Myelotoxicity Following Palliative Chemotherapy With Cisplatin and Gemcitabine in a Patient With Stage IV Cholangiocarcinoma Linked to Post Mortem Diagnosis of Fanconi Anemia
Unrecognized genome instability syndromes can potentially impede the rational treatment of cancer in rare patients. Identification of cancer patients with a hereditary condition is a compelling necessity for oncologists, giving varying hypersensitivities to various chemotherapeutic agents or radiation, depending on the underlying genetic cause. Omission of genetic testing in the setting of an overlooked hereditary syndrome may lead to unexpected and unbearable toxicity from oncological standard approaches. We present a case of a 33-year-old man with an early-onset stage IV intrahepatic cholangiocarcinoma, who experienced unusual bone marrow failure and neutropenic fever syndrome as a consequence of palliative chemotherapy containing cisplatin and gemcitabine, leading to a fatal outcome on day 25 of his first chemotherapeutic cycle. The constellation of bone marrow failure after exposure to the platinum-based agent cisplatin, the presence of an early-onset solid malignancy and the critical appraisal of further phenotypical features raised suspicion of a hereditary genome instability syndrome. Whole-exome sequencing from buccal swab DNA enabled the post mortem diagnosis of Fanconi anemia, most likely linked to the fatal outcome due to utilization of the DNA crosslinking agent cisplatin. The patient's phenotype was exceptional, as he never displayed significant hematologic abnormalities, which is the hallmark of Fanconi anemia. As such, this case stresses the importance to at least question the possibility of a hereditary basis in cases of relatively early-onset malignancy before defining an oncological treatment strategy
- …