150 research outputs found
Perspective on the physics of two-dimensional perovskites in high magnetic field
Two-dimensional (2D) metal halide perovskites consist of atomically thin layers composed of low bandgap metal-halide slabs, surrounded by high bandgap organic ligands, which behave as barriers. In this Perspective, we highlight how the use of large magnetic fields has been an extremely insightful tool to unravel some of the fundamental electronic properties of 2D perovskites. We focus on the combination of magnetoabsorption measurements and theoretical modeling to extract the carrier effective mass, on the use of magnetic field to clarify the fine structure of the exciton manifold, and on how magnetic fields can be helpful to correctly assign side peaks in the complex absorption or photoluminescence spectra displayed by 2D perovskites. We finally point out some challenges which might be successfully addressed by magneto-optical experimental techniques
Second order resonant Raman scattering in single layer tungsten disulfide (WS)
Resonant Raman spectra of single layer WS flakes are presented. A
second order Raman peak (2LA) appears under resonant excitation with a
separation from the E mode of only cm. Depending on the
intensity ratio and the respective line widths of these two peaks, any analysis
which neglects the presence of the 2LA mode can lead to an inaccurate
estimation of the position of the E mode, leading to a potentially
incorrect assignment for the number of layers. Our results show that the
intensity of the 2LA mode strongly depends on the angle between the linear
polarization of the excitation and detection, a parameter which is neglected in
many Raman studies.Comment: 6 pages, 4 figure
Microphotoluminescence study of disorder in ferromagnetic (Cd,Mn)Te quantum well
Microphotoluminescence mapping experiments were performed on a modulation
doped (Cd,Mn)Te quantum well exhibiting carrier induced ferromagnetism. The
zero field splitting that reveals the presence of a spontaneous magnetization
in the low-temperature phase, is measured locally; its fluctuations are
compared to those of the spin content and of the carrier density, also measured
spectroscopically in the same run. We show that the fluctuations of the carrier
density are the main mechanism responsible for the fluctuations of the
spontaneous magnetization in the ferromagnetic phase, while those of the Mn
spin density have no detectable effect at this scale of observation.Comment: 4 pages, 3 figure
The Fermi edge singularity of spin polarized electrons
We study the absorption spectrum of a two-dimensional electron gas (2DEG) in
a magnetic field. We find that that at low temperatures, when the 2DEG is spin
polarized, the absorption spectra, which correspond to the creation of spin up
or spin down electron, differ in magnitude, linewidth and filling factor
dependence. We show that these differences can be explained as resulting from
creation of a Mahan exciton in one case, and of a power law Fermi edge
singularity in the other.Comment: 4 pages, 4 figures, published in Phys. Rev. Let
Revealing large-scale homogeneity and trace impurity sensitivity of GaAs nanoscale membranes
III-V nanostructures have the potential to revolutionize optoelectronics and
energy harvesting. For this to become a reality, critical issues such as
reproducibility and sensitivity to defects should be resolved. By discussing
the optical properties of MBE grown GaAs nanomembranes we highlight several
features that bring them closer to large scale applications. Uncapped membranes
exhibit a very high optical quality, expressed by extremely narrow neutral
exciton emission, allowing the resolution of the more complex excitonic
structure for the first time. Capping of the membranes with an AlGaAs shell
results in a strong increase of emission intensity but also to a shift and
broadening of the exciton peak. This is attributed to the existence of
impurities in the shell, beyond MBE-grade quality, showing the high sensitivity
of these structures to the presence of impurities. Finally, emission properties
are identical at the sub-micron and sub-millimeter scale, demonstrating the
potential of these structures for large scale applications.Comment: just accepted in Nano Letters,
http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.7b0025
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
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