Ref HAL: hal-02275857_v1
DOI: 10.1038/s41467-019-11487-0
WoS: WOS:000478576500011
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8 Citations
Résumé:

InSe is a promising material in many aspects where the role of excitons is decisive. Here we report the sequential appearance in its luminescence of the exciton, the biexciton, and the P-band of the exciton-exciton scattering while the excitation power increases. The strict energy and momentum conservation rules of the P-band are used to reexamine the exciton binding energy. The new value >= 20 meV is markedly higher than the currently accepted one (14 meV), being however well consistent with the robustness of the excitons up to room temperature. A peak controlled by the Sommerfeld factor is found near the bandgap (similar to 1.36 eV). Our findings supported by theoretical calculations taking into account the anisotropic material parameters question the pure three-dimensional character of the exciton in InSe, assumed up to now. The refined character and parameters of the exciton are of paramount importance for the successful application of InSe in nanophotonics.

Ref HAL: hal-02272702_v1
Ref Arxiv: 1902.02974
DOI: 10.1021/acs.nanolett.9b00914
WoS: 000481563800013
Ref. & Cit.: NASA ADS
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1 Citation
Résumé:

Dipolar excitons offer a rich playground for both design of novel optoelectronic devices and fundamental many-body physics. Wide GaN/(AlGa)N quantum wells host a new and promising realization of dipolar excitons. We demonstrate the in-plane confinement and cooling of these excitons, when trapped in the electrostatic potential created by semitransparent electrodes of various shapes deposited on the sample surface. This result is a prerequisite for the electrical control of the exciton densities and fluxes, as well for studies of the complex phase diagram of these dipolar bosons at low temperature.

Ref HAL: hal-02182023_v1
DOI: 10.12988/astp.2019.918
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Résumé:

We calculate the trajectory of a moving object on earth and the trajectory of the earth around the sun in a fourdimensional space (x, y, z, t). We see that the trajectory has a mass: this is what is called dark matter which mass depends on the mass of the moving object. Indeed the deformation of space, the track, deviates light as we are at the hypersurface of the universe, and that is the method of measurement of the ’mass’ of the universe.

Ref HAL: hal-02167377_v1
DOI: 10.15407/spqeo22.02.237
WoS: WOS:000485818200011
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3 Citations
Résumé:

We have presented the results of terahertz time-domain spectroscopy measurements and a rigorous electrodynamic modeling of the optical characteristics of grating-based AlGaN/GaN plasmonic structures with low-doped two-dimensional electrongas in the frequency range of 0.1...1.5 THz. Two samples with grating aspect ratios (strip width/period) of 2.4/3 and 1.2/1.5 μm have been investigated. The measured transmission spectra are reconstructed in the calculations with high accuracy. The transmission spectrafor p-polarized incident radiation exhibits Fabri–Pérot oscillation behavior due to theoptically-thick substrate. The specific values of amplitude and spectral position of thetransmission maxima are associated with the coupling of terahertz radiation with 2Delectron gas due to plasmon excitations. Both calculations and transmission/reflectionmeasurements demonstrate that plasmonic structures with micro-scaled metallic gratinghave three-fold increase of non-resonant absorption of terahertz radiation in comparisonwith the bare heterostructure. The polarization measurements of the transmission spectra ofthe plasmonic structures well agree with calculations and indicate a well-pronounced filtering effect of the grating for the s-component of the incident electromagnetic wave. The obtained values of the transmission for p- and s-polarized incident radiation demonstrate the high quality of deposited metallic grating with the extinction ratio higher than 80:1 for sub- and few THz frequency range.

Ref HAL: hal-02157723_v1
DOI: 10.1134/S0021364019020085
WoS: WOS:000467096800005
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1 Citation
Résumé:

The features of terahertz photoluminescence and magnetoabsorption in magnetic fields up to 16 T in threelayer InAs/GaSb/InAs quantum wells with a band structure corresponding to a “two-dimensional semimetal” are studied. The comparison of the positions and amplitudes of the photoluminescence lines with the theoretical calculations of oscillator strengths for interband and intraband transitions performed using the eight-band Kane Hamiltonian indicates the existence of a nonradiative recombination channel associated with the overlap of the conduction and valence bands. The energies of interband and intraband Landau level transitions observed in the magnetoabsorption spectra are in good agreement with theoretical calculations, which confirms the predicted band structure.

Ref HAL: hal-02137172_v1
DOI: 10.1002/pssb.201800548
WoS: 000473612400011
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Résumé:

In a two dimensional electron gas, low energy transport in presence of a magnetic field occurs in chiral 1D channels located on the edge of the sample. In the AC description of quantum transport, the emittance determines the amplitude of the imaginary part of the admittance, whose sign and physical meaning are determined by the sample topology: a Hall bar is inductive while a Corbino ring is capacitive. In this article, the perfect capacitive character of Corbino samples in the quantum Hall effect regime is shown. A vanishing conductance and an electrochemical capacitance which depends on the density of states of 1D channels are measured. Our samples have no gate, neither on the side nor on the top, and the inner capacitances are measured. The transit time of electrons across the device is obtained and the drift velocity of carriers is deduced.

Ref HAL: hal-02137158_v1
DOI: 10.1002/pssb.201800509
WoS: 000473612400001
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Résumé:

Low‐temperature current–voltage characteristics of n‐type GaAs/GaAlAs quantum wells delta‐doped in GaAs channel with Be acceptors are studied in the presence of a magnetic field. Negatively charged acceptor ions localize 2D conduction electrons by a combined effect of a quantum well and magnetic field parallel to the growth direction. In acceptor‐doped samples, the Hall electric field plays the role of the gate voltage. It is shown that at magnetic fields as weak as 1.5 T (or higher), the drain current reaches a constant value independent of the drain voltage. This phenomenon is due to the electron localization resulting in the decrease of conducting electron density in the crossed‐field configuration. The above special behavior of acceptor‐doped GaAs/GaAlAs heterostructures is exploited to realize a device called Magnetic‐TEGFET (Magnetic Two‐dimensional Electron Gas Field Effect Transistor) operating at low temperatures. The elimination of the gate in the studied transistor suppresses the gate‐to‐drain leakage current, which, in the standard TEGFETs, results in the electronic shot noise.