Effects of electron-electron interactions on the electronic Raman scattering of graphite in high magnetic fields

We report the observation of strongly temperature (T)-dependent spectral lines in electronic Raman-scattering spectra of graphite in a high magnetic field up to 45 T applied along the c axis. The magnetic field quantizes the in-plane motion, while the out-of-plane motion remains free, effectively reducing the system dimension from 3 to 1. Optically created electron-hole pairs interact with, or shake up, the one-dimensional Fermi sea in the lowest Landau subbands. Based on the Tomonaga-Luttinger liquid theory, we show that interaction effects modify the spectral line shape from (ω-Δ)-1/2 to (ω-Δ)2α-1/2 at T = 0. At finite T, we predict a thermal broadening factor that increases linearly with T. Our model reproduces the observed T-dependent line shape, determining the electron-electron interaction parameter α to be ∼0.05 at 40 T. © 2014 American Physical Society.

High-temperature electron-hole liquid and dynamics of Fermi excitons in a In0.65Al0.35As/Al0.4Ga0.6As quantum dot array

State-filling effects of the exciton in a In0.65Al0.35As/Al0.4Ga0.6As quantum dot array are observed by quantum dot array photolumineseence at a sample temperature of 77 K. The exciton emission at low excitation density is dominated by the radiative recombination of the states in the s shell and at high excitation density the emission mainly results from the radiative recombination of the exciton state in the p shell. The spectral interval between the states in the s and p shells is about 30-40 mcV. The time resolved photoluminescence shows that the decay time of exciton states in the p shell is longer than that of exciton states in the s shell, and the emission intensity of the exciton state in the p shell is superlinearly dependent on excitation density. Furthermore, electron-hole liquid in the quantum dot array is observed at 77 K, which is a much higher temperature than that in bulk. The emission peak of the. recombination, of electron-hole liquid has an about 200 meV redshift from the exciton fluorescence. Two excitation density-dependent emission peaks at 1.56 and 1.59 eV are observed, respectively, which result from quantum confinement effects in QDs. The emission intensity of electron-hole liquid is directly proportional to the cubic of excitation densities and its decay time decreases significantly at the high excitation density.

Stimulated luminescence and photo-gated hole burning in BaFCl0.8Br0.2 : Sm2+,Sm3+ phosphors

The photo- and thermo-stimulated luminescence (PSL and TSL) of BaFCl0.8Br0.2:Sm2+,Sm3+ phosphors were investigated. It is found that the stimulated luminescence intensity of Sm2+ is almost equal to that of Sm3+ even if the content of Sm2+ is much lower than that of Sm3+. Only the stimulated luminescence of Sm2+ is observed in the sample in which the content of Sm2+ is much higher than Sm3+, demonstrating that the PSL or TSL efficiency of Sm2+ is much higher than that of Sm3+. This is attributed to the effective overlap of the e-h emission with the absorption of Sm2+ centers which may make the energy transfer from the electron-hole pairs to Sm2+ effectively. In BaFCl0.8Br0.2:Sm2+,Sm3+ the stimulated luminescence is considered to be occurred via the recombination of photoreleased electrons with the [Sm2+ + h] or [Sm3+ + h] complex and the energy transfer from the electron-hole pairs to the luminescence centers (Sm2+ and Sm3+) is concerned to be the major step to determine the stimulated luminescence efficiency. The X-ray-induced stimulated luminescence is compared and connected to the photon gated hole burning. The net result of the two processes is quite similar and may be comparable. It is suggested from the observations of stimulated luminescence that electron migration between Sm2+ and Sm3+ is not the major process, color centers may play an important role in hole burning. The information from stimulated luminescence is helpful for the understanding of the hole burning mechanism. (C) 1999 Elsevier Science Ltd. All rights reserved.

On detection wavelength and electron-hole wave function overlap of type II InAs/In-x Ga1-x Sb superlattice infrared photodetector

In this paper, the detection wavelength and the electron-hole wave function overlap of InAs/IrxGa1-xSb type II superlattice photodetectors are numerically calculated by using the envelope function and the transfer matrix methods. The band offset is dealt with by employing the model solid theory, which already takes into account the lattice mismatch between InAs and InxGa1-xSb layers. Firstly, the detection wavelength and the wave function overlap are investigated in dependence on the InAs and InxGa1-xSb layer thicknesses, the In mole fraction, and the periodic number. The results indicate that the detection wavelength increases with increasing In mole fraction, InAs and InxGa1-xSb layer thicknesses, respectively. When increasing the periodic number, the detection wavelength first increases distinctly for small periodic numbers then increases very slightly for large period numbers. Secondly, the wave function overlap diminishes with increasing InAs and InxGa1-xSb layer thicknesses, while it enhances with increasing In mole fraction. The dependence of the wave function overlap on the periodic number shows the same trend as that of the detection wavelength on the periodic number. Moreover, for a constant detection wavelength, the wave function overlap becomes greater when the thickness ratio of the InAs over InxGa1-xSb is larger.

Second harmonic generation in h-BN and MoS2 monolayers: Role of electron-hole interaction

We study second-harmonic generation in h-BN and MoS$_2$ monolayers using a novel \emph{ab initio} approach based on Many-body theory. We show that electron-hole interaction doubles the signal intensity at the excitonic resonances with respect to the contribution from independent electronic transitions. This implies that electron-hole interaction is essential to describe second-harmonic generation in those materials. We argue that this finding is general for nonlinear optical properties in nanostructures and that the present methodology is the key to disclose these effects.

Electron scattering and effects of sources of light on photoconductivity of SnO2 coatings prepared by sol-gel

Electro-optical properties of sol-gel derived 2 mol% antimony or niobium doped tin dioxide films have been measured. The electron density has been calculated considering all the relevant scattering mechanisms and experimental conductivity data measured in the range -197 to 25 degrees C. The results support the hypothesis that both ionised impurity scattering and grain boundary scattering have comparable effects in the resistivity of coatings, for free electron density congruent to 5 x 10(18) cm(-3). We have measured variation of photoconductivity excitation with wavelength using xenon and deuterium lamp as light sources. Results show that the main band in the photoconductivity spectrum is dependent on the spectral light source emission, the excitation peak reaching 5 eV (deuterium lamp). This band is due to the recombination process involving oxygen species and photogenerated electron-hole pairs. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Unconventional Hall effect near charge neutrality point in a two-dimensional electron-hole system

The transport properties of the two-dimensional system in HgTe-based quantum wells containing simultaneously electrons and holes of low densities are examined. The Hall resistance, as a function of perpendicular magnetic field, reveals an unconventional behavior, different from the classical N-shaped dependence typical for bipolar systems with electron-hole asymmetry. The quantum features of magnetotransport are explained by means of numerical calculation of the Landau level spectrum based on the Kane Hamiltonian. The origin of the quantum Hall plateau sigma(xy) = 0 near the charge neutrality point is attributed to special features of Landau quantization in our system.

Nonlocal Transport Near Charge Neutrality Point in a Two-Dimensional Electron-Hole System

Nonlocal resistance is studied in a two-dimensional system with a simultaneous presence of electrons and holes in a 20 nm HgTe quantum well. A large nonlocal electric response is found near the charge neutrality point in the presence of a perpendicular magnetic field. We attribute the observed nonlocality to the edge state transport via counterpropagating chiral modes similar to the quantum spin Hall effect at a zero magnetic field and graphene near a Landau filling factor nu = 0.

Search for high mass resonances decaying into electron-positron pairs in proton-proton collisions at sqrt(s) = 7 TeV with the ATLAS detector

The Standard Model of particle physics was developed to describe the fundamental particles, which form matter, and their interactions via the strong, electromagnetic and weak force. Although most measurements are described with high accuracy, some observations indicate that the Standard Model is incomplete. Numerous extensions were developed to solve these limitations. Several of these extensions predict heavy resonances, so-called Z' bosons, that can decay into an electron positron pair. The particle accelerator Large Hadron Collider (LHC) at CERN in Switzerland was built to collide protons at unprecedented center-of-mass energies, namely 7 TeV in 2011. With the data set recorded in 2011 by the ATLAS detector, a large multi-purpose detector located at the LHC, the electron positron pair mass spectrum was measured up to high masses in the TeV range. The properties of electrons and the probability that other particles are mis-identified as electrons were studied in detail. Using the obtained information, a sophisticated Standard Model expectation was derived with data-driven methods and Monte Carlo simulations. In the comparison of the measurement with the expectation, no significant deviations from the Standard Model expectations were observed. Therefore exclusion limits for several Standard Model extensions were calculated. For example, Sequential Standard Model (SSM) Z' bosons with masses below 2.10 TeV were excluded with 95% Confidence Level (C.L.).