Crossover between distinct mechanisms of microwave photoresistance in bilayer systems

We report on temperature-dependent magnetoresistance measurements in balanced double quantum wells exposed to microwave irradiation for various frequencies. We have found that the resistance oscillations are described by the microwave-induced modification of electron distribution function limited by inelastic scattering (inelastic mechanism), up to a temperature of T*~4 K. With increasing temperature, a strong deviation of the oscillation amplitudes from the behavior predicted by this mechanism is observed, presumably indicating a crossover to another mechanism of microwave photoresistance, with similar frequency dependence. Our analysis shows that this deviation cannot be fully understood in terms of contribution from the mechanisms discussed in theory.Comment: 7 pages, 4 figure

Magnetoresistance oscillations in multilayer systems - triple quantum wells

Magnetoresistance of two-dimensional electron systems with several occupied subbands oscillates owing to periodic modulation of the probability of intersubband transitions by the quantizing magnetic field. In addition to previous investigations of these magneto-intersubband (MIS) oscillations in two-subband systems, we report on both experimental and theoretical studies of such a phenomenon in three-subband systems realized in triple quantum wells. We show that the presence of more than two subbands leads to a qualitatively different MIS oscillation picture, described as a superposition of several oscillating contributions. Under a continuous microwave irradiation, the magnetoresistance of triple-well systems exhibits an interference of MIS oscillations and microwaveinduced resistance oscillations. The theory explaining these phenomena is presented in the general form, valid for an arbitrary number of subbands. A comparison of theory and experiment allows us to extract temperature dependence of quantum lifetime of electrons and to confirm the applicability of the inelastic mechanism of microwave photoresistance for the description of magnetotransport in multilayer systems.Comment: 10 pages, 5 figure

The role of mega projects in redefining housing development in Gulf cities

Since the end of the 1990s large scale mega projects have been initiated in Gulf cities to enable an unprecedented urban growth and the expansion of new economic sectors. In this respect, mega projects have played a key role in redefining housing developments in Gulf cities. This paper explores the newly emerging housing typologies and their distinctive roles in defining new urban environments. The selected case studies are located in the Jumeirah District in Dubai, which can be seen as the first prototype of a large cohesive development area that has been built of nine rather differing mega projects including the iconic Palm project and one of the largest residential high-rise agglomerations in the Middle East. The paper is based on the evaluation of official planning data from each project and field observations. Conclusions are drawn to highlight key implications while identifying housing development tendencies

Migrant Knowledge Workers’ Perceptions of Housing Conditions in Gulf Cities

© 2017, The Author(s). The various efforts in diversifying local economies in most Gulf States led to the emergence of new medium to high-income groups of migrant knowledge workers whose efforts are required to develop various new economic sectors. This paper aims to investigate the current housing conditions and perceptions of these migrant communities to identify key similarities and differences with respect to housing made available to them and depending on their cultural background. To this end, the methodology involves field surveys to explore the three main housing typologies for higher-income groups and a questionnaire with a total of 258 knowledge workers in the city of Doha as a representative case to investigate the associated perceptions of four dominant groups from different cultural backgrounds. The findings reveal that there is a distinct social segregation between cultural groups, which is mainly rooted in varying income levels. Furthermore, the supply-driven market has hardly integrated cultural needs of migrants and thus diversified and inclusive housing has been identified as major planning and design challenge

Thermally activated intersubband scattering and oscillating magnetoresistance in quantum wells

Experimental studies of magnetoresistance in high-mobility wide quantum wells reveal oscillations which appear with an increase in temperature to 10 K and whose period is close to that of Shubnikov-de Haas oscillations. The observed phenomenon is identified as magnetointersubband oscillations caused by the scattering of electrons between two occupied subbands and the third subband which becomes occupied as a result of thermal activation. These small-period oscillations are less sensitive to thermal suppression than the largeperiod magnetointersubband oscillations caused by the scattering between the first and the second subbands. Theoretical study, based on consideration of electron scattering near the edge of the third subband, gives a reasonable explanation of our experimental findings.Comment: 9 pages, 5 figure

Microwave zero-resistance states in a bilayer electron system

Magnetotransport measurements on a high-mobility electron bilayer system formed in a wide GaAs quantum well reveal vanishing dissipative resistance under continuous microwave irradiation. Profound zero-resistance states (ZRS) appear even in the presence of additional intersubband scattering of electrons. We study the dependence of photoresistance on frequency, microwave power. and temperature. Experimental results are compared with a theory demonstrating that the conditions for absolute negative resistivity correlate with the appearance of ZRS.Comment: 5 pages, 4 figure

Single-photon threshold photoionization of NO

Single‐photon threshold photoionization spectra for jet‐cooled NO have been measured for the v^+=0 and 1 vibrational levels of the X ^1Σ^+ ground state of NO^+. The NO^+ rotational state distribution for the v^+=0 level is shown to be perturbed by nearby autoionizing levels, whereas the v^+=1 level exhibits a cation rotational distribution which is in near quantitative agreement with calculated spectra near threshold. Only small changes in total angular momentum are observed (‖ΔJ‖=‖J^+ − J‘‖≤5/2) even though a wide range of photoelectron angular momenta (l=0–3) are predicted to contribute to the near‐threshold photoelectron continua. The present results are also discussed in light of recently published two‐photon threshold photoionization spectra of NO which exhibit nearly identical NO^+ rotational state distributions

Rotationally resolved threshold photoelectron spectra of OH and OD

The results of combined experimental and theoretical studies of the rotationally resolved photoelectron spectra of OH and OD following single‐photon ionization are presented. The measured zero‐kinetic‐energy (ZEKE) spectra were obtained using pulsed field ionization in conjunction with a vacuum ultraviolet laser source. The OH^+ and OD^+ (X ^3Σ^−, v^+=0) rotational distributions were studied over the range 95.0–95.4 nm. Agreement between the observed and calculated spectra is very encouraging. Improved values for the ionization potentials of OH and OD (104 989 and 105 085 ± 2 cm^(−1), respectively) are reported and the unusual dynamics favoring ΔN<0 transitions are discussed

A chronological exploration of the evolution of housing typologies in Gulf cities

This paper traces the evolution of housing typologies in four major cities in the Gulf region, namely Doha, Dubai, Abu Dhabi and Manama. The study reviews the formation and historical events in the region, which had a significant impact on new social as well as economic realities and consequently evolving housing types during the last two centuries. The methodological approach is based on reviewing a number of case studies representing local housing typologies throughout distinctive historic periods which were categorized in four periods: the post-nomadic, traditional, modern, and contemporary. The main objective is to identify the process of transformation by applying a comparative assessment of the different periods in order to examine continuities or ruptures between them. Thus, particular layout elements were analysed and compared. Conclusions are drawn to underline contemporary challenges while offering projections for future housing typologies in the selected cities and other similar ones

Non-linear transport phenomena in a two-subband system

We study non-linear transport phenomena in a high-mobility bilayer system with two closely spaced populated electronic subbands in a perpendicular magnetic field. For a moderate direct current excitation, we observe zero-differential-resistance states with a characteristic 1/B periodicity. We investigate, both experimentally and theoretically, the Hall field-induced resistance oscillations which modulate the high-frequency magneto-intersubband oscillations in our system if we increase the current. We also observe and describe the influence of direct current on the magnetoresistance in the presence of microwave irradiation.Comment: 8 pages, 6 figure