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OBJECTIVERandomized controlled trials (RCTs) form the basis of today’s evidence-based approach to medicine, and play a critical role in guidelines and the drug and device approval process. Conflicts of interest (COIs) are commonplace in medical research, but little is known about their influence. The authors aimed to evaluate the extent and influence of COIs in recent RCTs published in core neurosurgical journals using a cross-sectional analysis.METHODSThrough review of 6 general neurosurgical journals, all interventional RCTs published from January 2009 to January 2019 were identified. Because it is difficult to objectively assess study outcome, the authors opted for a strict rating approach based on the statistical significance of unambiguously reported primary endpoints, and the reported statistical protocol.RESULTSA total of 129 RCTs met the inclusion criteria. During the study period, the Journal of Neurosurgery published the largest number of RCTs (n = 40, 31%). Any potential COI was disclosed by 57%, and a mean of 12% of authors had a personal COI. Nonfinancial industry involvement was reported in 10%, while 31% and 20% received external support and sponsoring, respectively. Study registration was reported by 56%, while 51% of studies were blinded. Registration showed an increasing trend from 17% to 76% (p < 0.001). The median randomized sample size was 92 (interquartile range 50–153), and 8% were designed to investigate noninferiority or equality. Sixty-three RCTs (49%) unambiguously reported a primary endpoint, of which 13% were composite primary endpoints. In 43%, study outcome was positive, which was associated with a noninferiority design (31% vs 3%, p = 0.007) and a composite primary endpoint (46% vs 9%, p = 0.002). Potential COIs were not significantly associated with study positivity (69% vs 59%, p = 0.433). In the multivariate analysis, only a composite primary endpoint remained predictive of a positive study outcome (odds ratio 6.34, 95% confidence interval 1.51–33.61, p = 0.017).CONCLUSIONSThis analysis provides an overview of COIs and their potential influence on recent trials published in core neurosurgical journals. Reporting of primary endpoints, study registration, and uniform disclosure of COIs are crucial to ensure the quality of future neurosurgical randomized trials. COIs do not appear to significantly influence the outcome of randomized neurosurgical trials.

Electrolyte disorders are relatively frequent and potentially serious complications after pituitary surgery. Both DI (diabetes insipidus) and SIADH (syndrome of inappropriate antidiuresis) can complicate and prolong hospital and intensive care unit stay, and the latter may even be preventable. We aim to assess the incidence of both electrolyte disorders and their risk factors. From a prospective registry of patients who underwent endoscopic transnasal transsphenoidal surgery (TSS) for pituitary adenoma, patients with postoperative DI and SIADH were identified. Univariable and multivariable statistics were carried out to identify factors independently associated with the occurrence of either DI or SIADH. A total of 174 patients were included, of which 73 (42%) were female. Mean age was 54 years (range 20-88). During postoperative hospital stay, 13 (7.5%) patients presenting with DI and 11 (6.3%) with SIADH were identified. Patients who developed DI after surgery had significantly longer hospital stays (p = 0.022), as did those who developed SIADH (p = 0.002). Four (2.3%) patients were discharged with a diagnosis of persistent DI, and 2 (1.1%) with the diagnosis of SIADH. At the last follow-up, 5 (2.9%) patients presented with persistent DI, while none of the patients suffered from SIADH. Younger age (odds ratio (OR) 0.97, 95% confidence interval (CI) 0.94-1.01, p = 0.166) and pituitary apoplexy (OR 2.69, 95% CI 0.53-10.65, p = 0.184) were weakly associated with the occurrence of DI. We identified younger age (OR 0.96, 95% CI 0.92-0.99, p = 0.045) and lower preoperative serum sodium (OR 0.83, 95% CI 0.71-0.95, p = 0.008) as independent risk factors for SIADH. Although we found a weak association among age, pituitary apoplexy, and the occurrence of DI, no independent predictor was identified for DI. For postoperative SIADH however, lower age and preoperative serum sodium were identified as significant predictors. None of these findings were sufficiently supported by preexisting literature. Both electrolyte disorders are exquisitely hard to predict preoperatively, and further research into their early detection and prevention is warranted.

We have investigated the scattering mechanisms limiting the low-temperature electron mobility in unintentionally doped In 0.75 Al 0.25 As/In 0.75 Ga 0.25 As metamorphic quantum wells grown on GaAs (0 0 1) substrates. We found that the mobility is limited by background impurity scattering for densities lower than 2.0×10 11 cm −2 , and by the combination of this mechanism and alloy disorder scattering for higher densities. From such analysis we estimate an alloy disorder scattering potential of about 0.5±0.1 eV. Moreover we show that when a strained InAs layer is located in the centre of the In 0.75 Ga 0.25 As well, the alloy disorder scattering can be reduced, yielding mobilities up to 320 000 cm 2 /Vs at a carrier concentration of 3.1×10 11 cm −2 .

Electron spin resonance (ESR) is a natural candidate for quantum bit manipulation, provided that the confinement of a small number of electrons in a sufficiently small volume can be achieved. An important step is the development of low carrier density materials and structures in which the electron spins are isolated and can be controlled by ESR. We report on the realization of three low-density (n/sub 1/=1.77/spl times/10/sup 10/, n/sub 2/=4.5/spl times/10/sup 10/, and n/sub 3/=9/spl times/10/sup 10/ cm/sup -2/ without the help of a gate to deplete the channel) two-dimensional electron systems in GaAs-AlGaAs single quantum wells (QWs) and on the magnetoresistively detected electron spin resonance (MDESR) measurements in these samples. The MDESR has been characterized at /spl nu/=1 and /spl nu/=3 and the current intensity, microwave power, and temperature dependence have been studied. The structures that have been investigated represent the lowest density single QW samples in which MDESR has been detected. The implications of detection of the MDESR at such low electron density to coupled quantum-dot spin device technology will be presented.

We have investigated the infrared transmission of a two-dimensional (2DEG) electron gas confined in a $Al_{0.25}In_{0.75}As/Ga_{0.25}In_{0.75}As$ single quantum well in order to study the electron optical phonon interaction in a two phonon mode system. Infrared transmission experiments have been performed in both the perpendicular Faraday (PF) and tilted Faraday (TF) configurations for which the growth axis of the sample is tilted with respect to the incident light propagation direction and to the magnetic field direction. The experimental results lead to question the validity of the concept of polaron mass in a real material.

We use the circularly polarized resonant Rayleigh scattering (RRS) to study the quantum Hall ferromagnet at $\nu$ = 1. At this filling factor we observe a right handed copolarized RRS which probes the Skyrmion spin texture of the electrons in the photoexcited grounds state. The resonant scattering is not present in the left handed copolarization, and this can be related to the correlation between Skymionic effects, screening and spin wave excitations. These results evidence that RRS is a valid method for the study of the spin texture of the quantum Hall states.

Measurements of the microwave Hall mobility of semiconductors have been performed by an improved contactless method at 20 GHz by using a bimodal cavity resonator and a two-channel vector network analyzer. Data analysis was performed by using generalized expressions for the mobility, taking into account different coupling values on the two ports and a nonlinear response due to high magnetic fields in samples with mobility from thousands of cm2/V s. For several samples, Hall microwave and dc measurements have been compared, confirming the reliability of the proposed method; the characterization of bulk n-ZnSe and modulation-doped n-Al0.33Ga0.67As/GaAs two-dimensional electron gas samples is in particular presented. This method appears particularly suitable for the experimental determination of magnetotransport properties of semiconductor materials, especially when good electric contacts are difficult to be realized.

Increasing the ease and the rapidity of processing in micro and nanotechnology is an ongoing task, which is pursued in both the academic environment for investigation of novel systems and in industry for fabrication of complex circuits on a large scale. In the field of nanoelectronics, the major challenge is to demonstrate a feasible method for device implementation based on individual nanosize objects, such as nanowires, nanotubes and nanocrystals. However, integrating these small objects in a macroscopic circuit is a difficult task. So far, nanostructures have been wired by highly sophisticated techniques not suitable for large-scale integration in macroscopic circuits, such as electron-beam lithography or focused ion-beam deposition. Here we present a 'one-pot' and rapid approach to electrically interconnect individual nanowires from random spatial distribution, with high spatial and positioning resolution and a remarkable reduction in overall fabrication time with respect to the other expensive and laborious techniques. The reliability of such technique is demonstrated by implementing a single semiconductor nanowire device

The morphology and chemistry of S-treated GaAs(001) surfaces have been investigated by using an atomic force microscope (AFM) and a synchrotron radiation scanning photoemission microscope (SPEM) for a sample (A) which was directly blown dry with N 2 after the S-treatment and for another sample (B) which was rinsed by DI water and finally blown dry with N 2 after the S-treatment. AFM and SPEM images show for sample A a very inhomogeneous surface morphology, while the surface morphology of sample B appeared to be very homogeneous. On the surface of sample A, an inhomogeneous distribution of particles was observed by AFM. Nearly all these particles could be removed by the water rinse. Laterally resolved core level spectra analysis shows that on both samples the S bonds mainly to Ga. Only traces of As–S and As–As bonds exist at the sample surface while no S–S bonds could be detected. From the analysis of the O 1s core level it can be deduced that only a small GaAs surface fraction is oxidized. Furthermore, O–S bonds are present at the surface. On the sample before the water rinse, the number of O–S bonds is laterally inhomogeneously distributed. The number of O–S bonds can be drastically reduced by the water rinse, which also results in a homogeneous distribution of those bonds. We deduce that the O–S bonds belong to sulfate SO x deposits at the sample surface which are the particles that were imaged by AFM.

We investigated the structural and optical properties of Zn0.85Cd0.15Se epilayers for blue optical emission on lattice-matched InxGa1−xAs buffer layers. Both the II–VI layers and the III–V buffers were grown by molecular beam epitaxy on GaAs(001) wafers. A parabolic In concentration profile within the graded-composition InxGa1−xAs buffers was selected to control strain relaxation and minimize the concentration of threading dislocations. Dislocation-free II–VI growth was readily achieved on the graded buffers, with a Rutherford backscattering yield ratio reduced by a factor of 3 and a deep-level emission intensity reduced by over two orders of magnitude relative to those observed following direct II–VI growth on GaAs. The surface morphology of the materials, however, was found to replicate the crosshatched pattern of the underlying InxGa1−xAs substrates.

We present the operation of a new AlGaAs–GaAs multiquantum well hot-electron microwave detector. The working principle of this device is based on the interaction of two-dimensional free carriers inside the wells with the in-plane electric field. We shall report room-temperature responsivity of several 103V W− 1, comparable to that of conventional solid-state devices. The different physical principle of operation, however, yields for the present detector a broader frequency range, extending up to the submillimetre band, and short response times which can be estimated around 10 ps. Finally, we report a characterization of the device from the point of view of noise.

Lattice-matched ZnSe/InxGa1-xAs heterostructures were fabricated by molecular beam epitaxy on GaAs(001)2x4 surfaces. We find that the partial character of the strain relaxation within the ternary layer can be compensated by a suitable excess in the In concentration to match the free-surface lattice parameter to ZnSe. The surface of the II-VI epilayer, however, exhibits a cross-hatched pattern of surface corrugations oriented along orthogonal [110] directions. This complex surface morphology reflects the formation of surface slip steps during the nucleation of dislocation half-loops at the surface and the establishment of the misfit dislocation network at the InxGa1-xAs/GaAs interface. (C) 1998 American Institute of Physics.

The band discontinuities in ZnSe/AlAs(0 0 1) heterojunctions fabricated by molecular beam epitaxy are found to depend on the local interface composition in a manner reminescent of what was found earlier for ZnSe/GaAs(0 0 1) heterojunctions. Se-rich interface compositions correspond to valence band offsets as low as 0.2 eV, while Zn-rich interface compositions yield valence band offsets as high as 0.9 eV. When similar interface compositions are considered, the band offsets for ZnSe/AlAs and ZnSe/GaAs heterojunctions follow the predictions of the transitivity rule.

In 1− x Ga x As buffer layers grown on GaAs(0 0 1) wafers can be used as novel substrates lattice matched to the Zn 1− y Cd y Se active layers employed in blue-green lasers. Photoluminescence studies of Zn 1− y Cd y Se alloys ( x = 0.15 and 0.25) grown by molecular beam epitaxy on such substrates show a dramatic reduction in the deep-level emission as compared to Zn 1− y Cd y Se/GaAs(0 0 1) heterostructures. The surface of the epilayers, however, exhibits a cross-hatched morphology as a result of ∼ 10 nm deep surface corrugations oriented along perpendicular 〈1 1 0〉 directions.

We investigated the density and temperature dependence of biexciton recombination in Zn 1-x Cd x Se/ZnSe quantum wells grown by molecular beam epitaxy. Modulation-doped structures allowed us to investigate the electrostatic stability of biexcitons in the presence of a precise concentration of free carriers. Doping was introduced in the central part of the barrier up to a doping concentration of 3.4 x 10 18 cm 3 . The comparison between the two sets of samples allowed us to clarify the role of each elementary excitation as far as lasing is concerned. Although the biexciton binding energy in our undoped samples was sufficiently higher than in III-V materials, biexcitons are not stable at temperatures greater than 50 K. Moreover. the electrostatic screening and many-body effects caused by free-carriers decrease the biexciton binding energy so that biexcitons are not observed in modulation-doped samples. We found that the vicinity of the stimulated emission line at threshold with the peak of biexcitonic recombination, is not a sufficient criterion to conclude that lasing is biexcitonic in origin.

In this work we investigated the optical properties and lasing in graded-index separate confinement Zn 1-x Cd x Se/ZnSe heterostructures on In 1-x Ga x As (1 0 0) substrate. The carrier dynamics in the confining graded barriers and the single quantum well are investigated by using time-resolved photoluminescence measurements. Our measurements show the filling of quantum well states and depopulation of barrier states in about 25 ps. Moreover, we observed the reduction of the decay time of the photoluminescence as the excitation intensity was varied from below to above the threshold for lasing. Lasing threshold in these structures was found to be reduced by about one order of magnitude with respect to samples without graded-index profile. The threshold for lasing was in the range from 1 to 145 kW/cm 2 when the sample temperature was varied from 10 to 300 K. In short cavities, at temperatures higher than 150 K a transition from the first to the second quantized state was observed.

The exciton dynamics in Zn1 − xCdxSe/ZnSe multiple quantum wells have been investigated by temperature-dependent time-resolved photoluminescence experiments. A polariton effect (leading to a linearT-dependence of the decay time τPL) and thermal escape of carriers from the quantum well at relatively high temperature (resulting in a decrease of τPLwith the temperature) are observed in samples of different stoichiometry and well.

Photonic components based on structured metallic elements show great potential for device applications where field enhancement and confinement of the radiation on a subwavelength scale is required. In this paper, we report on a detailed study of a prototypical metallo-dielectric photonic structure, where features well known in the world of dielectric photonic crystals such as bandgaps and defect modes are exported to the metallic counterpart. Such a structure may have interesting applications in infrared science and technology, for instance, in quantum well infrared photodetectors, narrowband spectral filters, and tailorable thermal emitters.

Degradation defects induced by electron-beam bombardment in Zn1-xCdxSe/ZnSe (001) graded-index separate-confinement blue-green laser structures have been characterized by transmission electron microscopy. Most defects appear as tree-like arrangements of small extrinsic and intrinsic dislocation loops opening in +/-[100] or +/-[010] directions and are located within the quantum well or at its boundaries. The Burgers vectors of the loops were identified as b = 1/2[01(1) over bar] and b = 1/2[10(1) over bar] for defects opening in the +/-[100] and +/-[010] directions respectively.

Undoped and modulated-doped ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Se/ZnSe multiple quantum wells have been investigated in order to elucidate the role of biexcitons in the physical mechanism responsible for stimulated emission. Though biexcitons are clearly observed in undoped samples at 10 K, the temperature and density dependence of the intensity of the biexcitonic features clearly shows that in the normal operating conditions of quantum-well lasers biexcitons are not stable. Comparison of the energy of the stimulated emission in undoped versus modulation-doped samples allowed us to attribute the origin of lasing to the recombination of localized excitons.

We report transmission electron microscopy studies of native extended defects in pseudomorphic ZnSe/GaAs (001) and lattice-matched ZnSe-In0.04Ga0.96As (001) heterostructures. The dominant defects present in the layers were identified as Shockley stacking fault pairs lying on (111) and fault planes and single Frank stacking faults lying on or fault planes by comparing experimental images with the predictions obtained with the g.b = 0 rule as well as with simulated images.

We investigated the role of excitons, biexcitons and free-carriers in Zn 1–x Cd x Se/ZnSe multiple quantum well structures. By using stimulated emission measurements, pump and probe absorption spectroscopy, and magnetoluminescence we determined the threshold for exciton bleaching and lasing. The threshold for lasing resulted to be less than 10~kW~ cm –2 regardless of sample structure and composition, whereas the threshold for exciton bleaching was found to be larger or smaller than this value, depending on the exciton binding energy and localization effects. The competition between excitons, biexcitons and free-carriers in the stimulated emission processes is thus discussed in terms of a phase diagram model.

We investigated optical nonlinearities and stimulated emission in Zn 1− x Cd x Se/ZnSe multiple quantum well structures by using pump and probe transmission and high intensity photoluminescence (PL) measurements with or without magnetic field. We found that the origin of stimulated emission in the investigated samples depends on the exciton stability which can be increased by localization due to compositional and structural parameters. Exciton localization is directly demonstrated by time resolved PL measurements. A complex dynamics between excitons and free-carriers governs the physical mechanisms responsible for stimulated emission. This has been elucidated in detail by a many body theoretical model which has been used to analyze the experimental data based on an equilibrium phase diagram between excitons and free-carriers. Evidence of biexciton recombination is also given, and the stability of such excitonic molecules is investigated in modulation-doped quantum well structures.

We report the experimental realization of a nongalvanic, primary thermometer capable of measuring the electron temperature of a two-dimensional electron gas with negligible thermal load. Such a thermometer consists of a quantum dot whose temperature-dependent, single-electron transitions are detected by means of a quantum-point-contact electrometer. Its operating principle is demonstrated for a wide range of electron temperatures from 40 to 800 mK. This noninvasive thermometry can find application in experiments addressing the thermal properties of micrometer-scale mesoscopic electron systems, where heating or cooling electrons require relatively low thermal budgets. © 2013 American Physical Society.

Interesting phenomena during Au-assisted chemical beam epitaxy of InAs-InSb nanowire heterostructures have been observed. We observed an unusual nanowire density dependence of InSb nanowire length and rare non-monotonous type of the length-diameter dependence. Novel theoretical model of nanowire growth has been developed, which includes the contribution of readsorbtion of desorbed material from neighboring nanowire sidewalls.

The quantum-confined Stark effect~QCSE! in Zn 12xCd xSe/ZnSe multiple quantum wells embedded in the intrinsic region of p-i-n photodiodes has been investigated by means of photoluminescence spectroscopy under applied bias and photocurrent spectroscopy. Room-temperature excitonic bleaching is observed at reverse biases as low as 3 V. Both the redshift and the reduction of the oscillator strength of the excitonic emission have been calculated by means of a variational model. We use the same model to clarify the main specific features of the QCSE in II-VI materials. @S0163-1829~96!06847-6#

X‐ray reciprocal space mapping has been used to investigate the strain status of microgun‐pumped blue and blue‐green laser structures. The devices exploit graded‐index, separate confinement Zn1−xCdxSe/ZnSe heterostructures grown on InGaAs or GaAs substrates by molecular‐beam epitaxy. The location of the reciprocal lattice point of the ZnSe buffer layer within a normally forbidden region of reciprocal space indicates that the ZnSe buffer layer is unusually strained, with an appreciable biaxial tensile strain despite the smaller lattice parameter of the III–V substrate relative to ZnSe. We associate such a phenomenon with the presence of the highly strained laser structure coupled with preferential strain relaxation at the II–VI/III–V heterointerface.

Microgun-pumped blue lasers with lasing thresholds in the 4-20 kW/cm(2) range for temperatures between 83 and 225 K were fabricated by molecular beam epitaxy. The devices exploit graded index, separate confinement Zn1-xCdxSe/ZnSe heterostructures and use an array of low-voltage field-emission microtips for electron beam pumping. Degradation occurs through the formation of characteristic (100) dark-line defects, as in diode lasers. The device lifetime exceeded several hours at 83 K for a laser operating at 478.4 nm with a 12.5% duty-cycle.

The band discontinuities in ZnSeGaAs(100) heterostructures grown by molecular beam epitaxy depend on the local interface composition. We used a thin (20 A thick) composition control layer fabricated at the interface in Zn-rich or Se-rich conditions to control the band offsets for heterostructures in which the bulk of the II–VI epilayer was fabricated in stoichiometric growth conditions. Here we focus on the resulting variations in atomic interdiffusion across the interface, and on the local and long-range structural properties of the II–VI epilayer.

The Schottky barrier at Al/Zn 1-x Cd x Se junctions was determined through high resolution synchrotron radiation photoemission studies of interfaces fabricated in situ on atomically clean, Se-rich surfaces. A gradual decrease in the n-type barrier with increasing x reflects the bandgap variation in the ternary alloy and the band alignment in Zn 1-x Cd x Se/ZnSe heterojunctions. Correspondingly, transport studies of Al/n-Zn 1-x Cd x Se contacts fabricated ex situ show a dramatic decrease of the specific contact resistance with increasing x. Improved performance of Al/n-ZnSe contacts can therefore be achieved through fabrication of graded Zn 1-x Cd x Se layers at the interface.

The electrical properties of nanowire-based n-InSb-n-InAs heterojunctions were investigated theoretically and experimentally. Analysis of the current-voltage characteristics showed that the current through the heterojunction is caused mostly by generation-recombination processes in the InSb and at the heterointerface. Due to the partially overlapping valence band of InSb and the conduction band of InAs, the second process is fast and activationless. Theoretical analysis showed that, depending on the heterojunction parameters, the flux of non-equilibrium minority carriers may have a different direction, explaining the experimentally observed non-monotonic coordinate dependence of the electron beam induced current. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795123]

We investigated the effect of the free-electron density on the heavy-hole exciton transitions in n-type, modulation-doped ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cd}}_{\mathit{x}}$Se/ZnSe multiple quantum wells. Exciton binding energy and oscillator strength were determined from optical-absorption spectra and were found to be strongly influenced by the free-carrier concentration. Complete saturation of the excitonic absorption could be induced at sufficiently high doping levels. Comparison with theoretical predictions suggests that phase-space filling and short-range exchange interactions may account for exciton bleaching. The corresponding critical density was found to increase with Cd content as a consequence of the increasing exciton stability.

We investigated exciton stability and the recombination mechanism responsible for lasing in Zn 1-x Cd x Se/ZnSe multiple quantum well structures grown by molecular beam epitaxy. We used photocurrent measurements as a function of sample composition and temperature to gauge exciton stability, and photoluminescence and magnetophotoluminescence spectroscopy to identify the recombination channels associated with stimulated emission. For relatively shallow quantum wells (x∼0.10), the spontaneous emission line shifts diamagnetically with the magnetic field as expected for exciton-related transitions. On the contrary, the stimulated emission exhibits a linear shift with the magnetic field which is consistent with free-carrier recombination from Landau levels

Systematic temperature-dependent studies of optical absorption and photoluminescence in ${\mathrm{Zn}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cd}}_{\mathit{x}}$Se/ZnSe strained-layer multiple-quantum-well samples grown by molecular-beam epitaxy were used to evaluate the well-width dependence and the composition dependence of the major excitonic properties. Exciton binding energies calculated by means of a variational method were found in good agreement with the experimental values obtained from the analysis of the absorption line shapes. The well-width dependence of the excitonic eigenstates were well reproduced by envelope-function calculations that included the effect of pseudomorphic strain.

International audience; Heterostructured InAs/InSb nanowire (Nw) based field effect transistors (FET) have been fabricated and tested as Terahetz radiation detectors. While responsivity and noise equivalent power compare with the ones of InAs nanowire detectors, the presence of small-gap InSb semiconductor gives rise to interesting physical effects such an increase of the detected signal with charge injection through the wire, at odds with standard FET-detectors. Additionally, the photodetected signal voltage changes its sign after a threshold gate bias, which we explain considering surface-related transport and field asymmetries imposed by the use of a lateral gate electrode.

We experimentally investigate the temperature (T) dependence of the resistance of a classical ballistic point contact (PC) in a two-dimensional electron system (2DES). The split-gate PC is realized in a high-quality AlGaAs/GaAs heterostructure. The PC resistance is found to drop by more than 10% as T is raised from 0.5 K to 4.2 K. In the absence of a magnetic field, the T dependence is roughly linear below 2 K and tends to saturate at higher T. Perpendicular magnetic fields on the order of a few 10 mT suppress the T-dependent contribution ?R. This effect is more pronounced at lower temperatures, causing a crossover to a nearly parabolic T dependence in a magnetic field. The normalized magnetic field dependencies ?R(B) permit an empiric single parameter scaling in a wide range of PC gate voltages. These observations give strong evidence for the influence of electron-electron (e-e) scattering on the resistance of ballistic PCs. Our results are in qualitative agreement with a recent theory of the e-e scattering based T dependence of the conductance of classical ballistic PCs [ Phys. Rev. Lett. 101 216807 (2008) and Phys. Rev. B 81 125316 (2010)].

We have investigated the transition from strong to ultra-strong coupling regime between a mid-infrared intersubband excitation and the fundamental mode of a metal-dielectric-metal microcavity. The ultra-strong coupling regime is demonstrated up to room temperature for a wavelength of $11.7 \mu$m by using 260 nm thick cavities, which impose an extreme sub-wavelength confinement. By varying the doping of our structures we show that the experimental signature of the transition to the ultra-strong coupling regime is the opening of a photonic gap in the polariton dispersion. The width of this gap depends quadratically on the ratio between the Rabi and intersubband transition energies.

We experimentally realize quantum Hall Mach-Zehnder interferometer which operates far beyond the equilibrium. The operation of the interferometer is based on allowed intra-edge elastic transitions within the same Landau sublevel in the regime of high imbalances between the co-propagating edge states. Since the every edge state is definitely connected with the certain Landau sublevel, the formation of the interference loop can be understood as a splitting and a further reconnection of a single edge state. We observe an Aharonov-Bohm type interference pattern even for low-size interferometers. This novel interference scheme demonstrates high visibility even at millivolt imbalances and survives in a wide temperature range., Comment: As accepted by PRB

Intersubband cavity polaritons in a quantum well waveguide structure are optically generated within less than one cycle of light by a 12-femtosecond near-infrared pulse. Mid-infrared probe transients trace the nonadiabatic switch-on of ultrastrong light-matter coupling and the conversion of bare photons into cavity polaritons directly in the time domain. Future perspectives of room-temperature subcycle control of ultrastrong electron-photon interaction are discussed. (C) 2011 American Institute of Physics. [doi :10.1063/1.3578341]

We use the circularly polarized resonant Rayleigh scattering (RRS) to study the quantum Hall ferromagnet at ? = 1. At this filling factor, we observe a right-handed copolarized RRS which probes the Skyrmion spin texture of the electrons in the photoexcited ground states. The resonant scattering is not present in the left-handed copolarization, and this can be related to the correlation between Skymionic effects, screening, and spin wave excitations. These results evidence that RRS is a valid method for the study of the spin texture of the quantum Hall states.

The dislocation microstructure associated with the loss of coherency of CdTe(001), as grown on GaAs(001), is characterized using high-resolution trans-mission electron microscopy. The examination of cross-sectional specimens allowed characteristic local variations in the relative orientation of the overgrowth and the substrate to be quantified and related to associated local changes in the form and distribution of the interface dislocation array. In the interface array, the relative proportion of 60° dislocations and Lomer-Cottrell locks proved to be related to the local misorientation between the CdTe and GaAs. The extent to which this is indicative of the mode of stress relief during the loss of coherency is discussed. Interestingly, it was also found that such variations in the relative proportions of the different types of dislocation proved to be associated with microtwin formation. The significance of this with regard to the strain relief mechanism is also noted.

Controlling the way light interacts with material excitations is at the heart of cavity quantum electrodynamics (cavity QED). In the strong coupling regime, quantum emitters inside a microresonator coherently absorb and reemit a photon many times before dissipation becomes effective. The resulting mixed light-matter states (polaritons) are studied in a broad context ranging from atomic [1] to solid state systems [2, 3] and inspire next-generation optoelectronic devices [4]. Thanks to intersubband transitions, we have recently demonstrated that semiconductor microcavities can reach a new limit of ultrastrong coupling, where light-matter exchange occurs on a time scale comparable with the oscillation period of light itself [5]. Remarkably, the anti-resonant and A square terms of the interaction Hamiltonian produce observable anomalies of the polariton dispersion even in a few photon experiment performed at room temperature. In this regime, ultrafast modulation of the coupling strength is predicted to reveal unprecedented QED phenomena [6] reminiscent of the dynamical Casimir effect [7] or Unruh-Hawking radiation of black holes [8]. Yet, up to now, QED devices switchable on sufficiently short times have not been available. Exploiting a semiconductor quantum well waveguide structure we experimentally show how to optically tune light-matter interaction from weak to ultrastrong and turn on maximum coupling within less than one cycle of light [9]. Using electro-optic detection one can also directly monitor, in the time domain, how a coherent photon population converts to cavity polaritons during abrupt switching. This system represents then a first promising laboratory for a new class of non-adiabatic QED effects and provides an efficient room-temperature switching device at the ultimate speed. The work was performed together with G. Gunter, A. A. Anappara, J. Hees, G. Biasiol, L. Sorba, S. De Liberato, C. Ciuti, A. Leitenstorfer, and R. Huber.