Spin coherence of holes in GaAs/AlGaAs quantum wells

The carrier spin coherence in a p-doped GaAs/(Al,Ga)As quantum well with a diluted hole gas has been studied by picosecond pump-probe Kerr rotation with an in-plane magnetic field. For resonant optical excitation of the positively charged exciton the spin precession shows two types of oscillations. Fast oscillating electron spin beats decay with the radiative lifetime of the charged exciton of 50 ps. Long lived spin coherence of the holes with dephasing times up to 650 ps. The spin dephasing time as well as the in-plane hole g factor show strong temperature dependence, underlining the importance of hole localization at cryogenic temperatures.Comment: 5 pages, 4 figures in PostScript forma

Verification of band offsets and electron effective masses in GaAsN/GaAs quantum wells : Spectroscopic experiment versus 10-band k.p modeling

Optical transitions in GaAs1-xNx/GaAs quantum wells (QWs) have been probed by two complementary techniques, modulation spectroscopy in a form of photoreflectance and surface photovoltage spectroscopy. Transition energies in QWs of various widths and N contents have been compared with the results of band structure calculations based on the 10-band k.p Hamiltonian. Due to the observation of higher order transitions in the measured spectra, the band gap discontinuities at the GaAsN/GaAs interface and the electron effective masses could be determined, both treated as semi-free parameters to get the best matching between the theoretical and experimental energies. We have obtained the chemical conduction band offset values of 86% for x = 1.2% and 83% for x = 2.2%, respectively. For these determined band offsets, the electron effective masses equal to about 0.09 m(o) in QWs with 1.2% N and 0.15 m(o) for the case of larger N content of 2.2%.Publisher PDFPeer reviewe

Exciton lifetime and emission polarization dispersion in strongly in-plane asymmetric nanostructures

We present experimental and theoretical investigation of exciton recombination dynamics and the related polarization of emission in highly in-plane asymmetric nanostructures. Considering general asymmetry- and size-driven effects, we illustrate them with a detailed analysis of InAs/AlGaInAs/InP elongated quantum dots. These offer a widely varied confinement characteristics tuned by size and geometry that are tailored during the growth process, which leads to emission in the application-relevant spectral range of 1.25-1.65 {\mu}m. By exploring the interplay of the very shallow hole confining potential and widely varying structural asymmetry, we show that a transition from the strong through intermediate to even weak confinement regime is possible in nanostructures of this kind. This has a significant impact on exciton recombination dynamics and the polarization of emission, which are shown to depend not only on details of the calculated excitonic states but also on excitation conditions in the photoluminescence experiments. We estimate the impact of the latter and propose a way to determine the intrinsic polarization-dependent exciton light-matter coupling based on kinetic characteristics.Comment: 11 pages, 8 figure

The contribution of multiple barriers to reproduction between edaphically divergent lineages in the Amazonian tree \u3cem\u3eProtium subserratum\u3c/em\u3e (Burseraceae)

Disentangling the strength and importance of barriers to reproduction that arise between diverging lineages is central to our understanding of species origin and maintenance. To date, the vast majority of studies investigating the importance of different barriers to reproduction in plants have focused on short-lived temperate taxa while studies of reproductive isolation in trees and tropical taxa are rare. Here, we systematically examine multiple barriers to reproduction in an Amazonian tree, Protium subserratum (Burseraceae) with diverging lineages of soil specialist ecotypes. Using observational, molecular, distributional, and experimental data, we aimed to quantify the contributions of individual prezygotic and postzygotic barriers including ecogeographic isolation, flowering phenology, pollinator assemblage, pollen adhesion, pollen germination, pollen tube growth, seed development, and hybrid fitness to total reproductive isolation between the ecotypes. We were able to identify five potential barriers to reproduction including ecogeographic isolation, phenological differences, differences in pollinator assemblages, differential pollen adhesion, and low levels of hybrid seed development. We demonstrate that ecogeographic isolation is a strong and that a combination of intrinsic and extrinsic prezygotic and postzygotic barriers may be acting to maintain near complete reproductive isolation between edaphically divergent populations of the tropical tree, P. subserratum

Influence of carrier concentration on properties of InAs waveguide layers in interband cascade laser structures

The work has supported by the European Commission within the Project WideLase (No. 318798) of the 7-th Framework Programme and by the National Science Center of Poland by the Grant No. 2014/15/B/ST7/04663.We present a characterization of doped InAs layers in interband cascade lasers exploiting the plasmon-enhanced waveguiding. Fast differential reflectance was employed in order to identify the plasma-edge frequency via the Berreman effect and shown as an advantageous method when compared to other types of measurements. The carrier concentration was then derived and compared with the nominal doping densities. The emission properties of the investigated structures were studied by means of photoluminescence (PL). Its full-width at half-maximum and integrated intensity were extracted from PL spectra and analyzed in the function of the doping density (carrier concentration). The PL linewidth was found to be independent of the carrier concentration indicating an insignificant contribution of doping to the structural properties deterioration. The PL intensity decay with the carrier concentration suggests being dominated by Auger recombination losses.PostprintPeer reviewe

ANNA Tool: A Way to Connect Future and Past Students in STEM

The 'Increasing Gender Diversity in STEM' project involved six different partner universities around Europe. The scope of the project was to investigate the gender difference in self-perception of students in relation to their career choice. This was done through a web-based app, ANNA tool, that allows high school students to match their own personality, views, and expectations to those of engineering students and professional engineers. In the meantime, the data collection gave the opportunity to take a look at how students perceive their university and undergraduate program. This pilot application is then been further studied in order to analyse its scalability in other countries with broader STEM content

Controlled traffic farming delivers better crop yield of winter bean as a result of improved root development

This paper reports on the continuation of a long–term experiment on the effects of alternative field traffic systems (STP–random traffic with standard tyre inflation pressure, LTP–random traffic with low tyre inflation pressure and CTF–controlled traffic farming) on soil conditions and crop development as influenced by different tillage depths (DEEP–250 mm, SHALLOW–100 mm and ZERO–tillage), in a randomised 3 x 3 factorial design in 4 replicates launched by Harper Adams University in Edgmond, UK, in 2011. The results from season 2017–2018 revealed that CTF delivered 8% higher crop yield of winter field bean (Vicia faba) cv. Tundracomparing to STP (p = 0.005), i.e. 4.13 vs 3.82 tonnes ha-1respectively (at 14% moisture content). The ZERO–tillage plots featured significantly lower plant establishment percentage comparing to shallow and deep tillage: 79% vs 83% and 83% respectively (p = 0.012). The research showed that roots traits differed significantly between contrasting traffic at depths greater than 50mm with p < 0.05of: tap root biomass, number of lateral roots, biomass of lateral roots as well as total root biomass (tap+lateral roots),delivering significantly greater values of those before mentioned parameters on CTF comparing to STP. Tap root length significantly differed between traffic systems (p < 0.001)giving significantly greater results on CTF comparing to LTP and STP (17.7, 13.4 and 12.6 mm respectively). Significant differences in tap root diameter were found only at the depth of 100 mm (p < 0.001) where again CTF delivered significantly higher root diameter than the remaining 2 traffic systems.In the shallow layer of soil (0–50 mm) a significant difference was found only for tap root biomass, for interactions, where STP ZERO gave significantly higher results than STP SHALLOW and CTF SHALLOW (1.430, 0.733 and 0.716 g respectively)