Intermediate Gap Research Articles

Thermal stability of quaternary alloy (InAlGaAs)-capped InAs/GaAs multilayer quantum dot heterostructures with variation in growth rate, barrier thickness, seed quantum dot monolayer coverage, and post-growth annealing

Strain-driven influences on the structural and optoelectronic properties of self-assembled InAs/GaAs multilayer quantum dot (MQD) heterostructures prompted our research into the growth of thermally stable MQD samples that were functional in an emission range technically favorable for communication lasers and intermediate band gap solar cells. We also studied parameter optimization by varying growth rate, capping layer thickness, seed quantum dot (QD) monolayer coverage, and post-growth annealing. A capping combination of InAlGaAs and i-GaAs was used. This combination helps in strain compensation, favors growth of multiple QD layers, functions as a strain-driven phase separation alloy, and helps increase QD stability. Photoluminescence results showed MQD sample emissions in the technologically significant range of 1.1–1.3 μm. Post-growth annealing at high temperatures led to inter-diffusion of the constituent QD materials, generation of low minimum energy states, and greater carrier involvement in intermediate band gap structures, thereby showing that annealing is a suitable method for post-growth manipulation. For one MQD sample, the annealing temperature was found to affect structural and optoelectronic properties as well as the presence of intermediate energy states. Heterostructure stability at annealing temperatures up to 750 ∘C was found for the other samples. Transmission electron microscopy and photoluminescence results supported these findings.

A new twist on Stokes’ second problem: Partial penetration of nonlinearity in sheared viscoelastic layers

Fully nonlinear flow-constitutive model simulations are employed to investigate constructive and destructive interference of counter-propagating shear waves and their associated stress profiles within a viscoelastic layer of “intermediate depth”. Linear unidirectional shear waves in sufficiently thick viscoelastic layers, the viscoelastic analog of Stokes’ second problem, were exploited as a rheological tool by Ferry et al. [1,2]. The extension to intermediate gap heights for linear and nonlinear driving amplitudes was studied by our group [3–5], and by Balmforth et al. [6] for viscoplastic fluids. Here we explore the nonlinear quasi-stationary response of the entire viscoelastic layer to an oscillating boundary, greater than the gap-loading limit of typical shear rheometers but less than the depth of effective attenuation. We illustrate how to tune the degree and partitioning of nonlinearity versus driving amplitude and frequency, gap height, and fluid viscoelasticity.

Responses of soil respiration and its temperature sensitivity to thinning in a pine plantation

Understanding the effects of forest management practice on soil respiration (Rs) and its temperature sensitivity (Q10) is crucial for the accurate estimation of the global carbon budget. However, the dynamics of Rs and Q10 resulting from plantation thinning are not well understood. To evaluate the impacts of forest thinning on Rs and Q10, we selected a pine plantation in the eastern Tibetan Plateau and applied the technique of thinning by simulating gap formation. We measured Rs monthly before (from July to November 2008) and after (from December 2008 to June 2012) thinning, combining with monthly microclimatic factors. Rs showed significant seasonal variability (P<0.001) in both control (0.30±0.05 to 2.94±0.29μmolCm−2s−1) and thinned (0.25±0.04 to 2.99±0.08μmolCm−2s−1) stands, with higher rates from July to September and lower rates from December to February. These seasonal dynamics were primarily driven by soil temperature rather than by moisture limitation, except during an especially dry season, when soil moisture significantly affected Rs. There were significant differences in Rs during the growing season between the control and thinned sites following thinning. Rs increased at the thinned sites compared with the control sites during the summer of the first and the third year following thinning; however, Rs decreased at the thinned sites in the second summer. This suggested that climatic variability, such as change in soil moisture induced from thinning, played an important role in controlling Rs. There was no significant difference (P=0.083) in Rs between control and thinned treatments after thinning (December 2008 to June 2012). For example, averages of Rs were 1.19±0.34, 1.20±0.36, 1.16±0.38μmolCm−2s−1 in the control, small gap and intermediate gap treatments, respectively. In addition, the short-term Q10 showed a significantly seasonal variability (P<0.001) and was altered by thinning (P=0.048). The long-term Q10 also showed a significant inter-annual variability (P<0.001), while thinning did not affect it. During the study period (December 2008 to June 2012), the Q10 values for the small and intermediate gaps significantly increased by 13.9% and 25.9% (P<0.05), respectively, compared with the control. These results suggest that the forest thinning by simulating natural gap formation has a relatively small impact on soil CO2 emission and its temperature sensitivity in comparison to the greater influence of inter-annual climatic variability.

Analysis of the temperature-dependence of P+HA− charge recombination in the Rhodobacter sphaeroides reaction center suggests nanosecond temperature-independent protein relaxation

The temperature dependence of charge recombination of the pair P(+)HA(-) in isolated reaction centers from the purple bacterium Rhodobacter sphaeroides with prereduced quinone QA was studied by sub-nanosecond to microsecond time-scale transient absorption. Overall, the kinetics slowed down substantially upon cooling from room temperature to ∼200 K, and then remained virtually unchanged down to 77 K, indicating the coexistence of two competitive pathways of charge recombination, a thermally-activated pathway appearing only above ~200 K and a temperature-independent pathway. In our modelling, the thermally activated pathway includes an uphill electron transfer from HA(-) to BA(-) leading to transient formation of the state P(+)BA(-), whereas the temperature-independent pathway is due to direct downhill electron transfer from HA(-) to P(+). At all temperatures studied, the kinetics could be approximated by a four-component decay. Detailed analysis of the lifetimes and amplitudes of particular phases over the range of temperatures suggests that the kinetically resolved phases reveal the consecutive appearance of three conformational states characterized by an increasing free energy gap between the states P(+)BA(-) and P(+)HA(-). The initial gap between these states was estimated to be only ~8 meV, the intermediate gap being ~92 meV, and the final gap ~135 meV, with no dependence on temperature. It was also calculated through a very straightforward approach that the relaxation process from the initial to the intermediate state occurs within 0.6 ± 0.1 ns, whereas the second step of relaxation from the intermediate to the final state takes 11 ± 2 ns. Both phases of the protein relaxation process are essentially temperature-independent. Possible alternative models to describe the experimental data that cannot be definitely excluded are also discussed.

Investigation of Quantum Dot Solar Cell Device Performance

ABSTRACTThe device performance of GaAs p-i-n solar cells containing stacked layers of self-assembled InAs quantum dots is investigated. The solar cells demonstrate enhanced external quantum efficiency below the GaAs band gap relative to a control device without quantum dots. This is attributed to the capture of sub-band gap photons by the quantum dots. Analysis of the current density versus voltage characteristic for the quantum dot solar cell reveals a decrease in the series resistance as the device area is reduce from 0.16 cm2 to 0.01 cm2. This is effect is not observed in control devices and is quantum dot related. Furthermore, low temperature measurements of the open circuit voltage for both quantum dot and control devices provide experimental verification of the conditions required to realise an intermediate band gap solar cell.

Preparation, electronic structure and photoluminescence properties of RE (RE = Ce, Yb)-activated SrAlSi4N7 phosphors

The electronic structure of SrAlSi4N7 was calculated using the CASTEP code and SrAlSi4N7 is an intermediate band gap semiconductor with an indirect energy gap of 3.6 eV. Ce3+ and Yb2+-activated SrAlSi4N7 samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. SrAlSi4N7:Ce3+ shows a broad band emission in the wavelength range of 450–700 nm, originating from the 5d1–4f1 transition of Ce3+. The emission band of Ce3+ shifts to longer wavelength with an increase of Ce3+ concentration due to the increased Stokes shift and reabsorption by Ce3+. SrAlSi4N7:Yb2+ can be excited efficiently over a broad spectral range between 300 and 550 nm, and exhibits a single intense red emission at 600 nm with a full width at half maximum of 95 nm due to the electronic transitions from the excited state of 4f135d to the ground state 4f14 of Yb2+. The low energy of Yb2+ emission in SrAlSi4N7 can be attributed to the large nephelauxetic effect and crystal field splitting due to the coordination of Yb2+ by nitrogen. In addition, Sr1−2xCexLixAlSi4N7 shows higher thermal stability in air than that of Sr1−yYbyAlSi4N7 (0 ≤ x, y ≤ 0.1). A white-light LED can be generated by using single SrAlSi4N7:Ce3+ as the wavelength conversion phosphor combined with a blue LED chip (InGaN). The obtained LED exhibits a luminous efficiency of 74.3 lm W−1 at a corrected color temperature (CCT) up to 6350 K, and the color rendering index (CRI Ra) is around 78. These novel developed yellow-red phosphors have potential applications in spectral conversion materials for white-LEDs.

Numerical Study of the Effect of Wedge Angle of a Wedge-Shaped Body in a Channel using Lattice Boltzmann Method

The aim of this paper is to study the fluid flow behavior around a wedge shaped body with different wedge angles placed in a channel using Lattice-Boltzmann Method (LBM). The LBM has built up on the D2Q9 model and the single relaxation time method called the Lattice-BGK (Bhatnagar-Gross-Krook) model. The influence of the gap ratio G* = G/H, where H is the distance between two parallel walls, G is the gap between body and wall, on the flow field is illustrated. The gap ratio, G*, depends on the angle of wedge-shaped body (0° < < 180°). Streamlines, vorticity contours and pressure contours are provided to analyze the important characteristics of the flow field for a wide range of non dimensional parameters namely the Reynolds number (Re), Strouhal number (St) and the gap ratio(G*). However, it is seen that the flow can be characterized by three regions: (i) large gap ratio, 0.44 < G* < 0.50, with 0° < < 55°, (ii) intermediate gap ratio, 0.20 G* 0.44, with 55° 120° and (iii) small gap ratio, 0 < G* < 0.20, with 120° < < 180°. The simulation results are compared with experimental data and other numerical models and found to be very reasonable and satisfactory.

EVALUATION OF DEVELOPED OILSEED EXPRESSION MACHINE

The aim of this study was to develop and test an oilseed expression machine for oil production. The tested parameters were: (1) Machine setting of one stage and double stage expression (2) Screw speeds of 30, 50, 70 and 90 rpm (3) Cake output clearance 0.5, 0.8, 1.1 and 1.4 mm (4) for double stage expression setting intermediate choke gap of 0.6, 0.8, 1.0 and 1.2 mm. and (5) Moisture content of oilseed 6 %, 8% and 10%. Results obtained increasing in expression efficiency by: reducing the choke gap, reducing the screw rotational speed, increasing seeds moisture-content to 8% (d.b),and using double stage machine. Maximum oil expression efficiency was 86% at 0.5 mm choke gap, 30 rpm screw rotational speed, 6% moisture content and two stage machine setting with 0.6 mm intermediate choke gap. On the other hand, minimum oil expression efficiency was 52% at 1.4 mm choke gap, 90 rpm screw rotational speed, 6% moisture content and single stage machine. The evaluated parameters affecting the expression process, oil productivity, expression efficiency, expressed oil temperature, oil production cost are discussed in the paper.

A study of the effect of the jet-like flow on the near wake behind a circular cylinder close to a plane wall

The flow around a circular cylinder placed near a plane wall has been investigated experimentally using PIV, with the purpose of studying the jet-like flow that takes place in the gap between the cylinder and the wall and its effects on the wake flow. The Reynolds number based on the diameter of the cylinder, D, and the incoming flow velocity was about 8700. The gap size, G, between the cylinder and the plane wall was varied between G/D=0.15 and 1.00. The results showed the existence of three distinct flow regimes as the cylinder-wall gap size is varied: (1) The large gap flow regime (G/D>0.8) in which the vortex shedding is nearly symmetric. Small influence of the wall has been detected in this flow regime; (2) The intermediate gap flow regime (0.3<G/D<0.8) in which the vortex shedding becomes intermittent with the appearance of small structures due to the transition of the elongated shear layers; and (3) The small gap flow regime (G/D<0.3) in which the jet like-flow destroys the lower shear layer and prevents the onset of the alternating vortex shedding. The proper orthogonal decomposition (POD) analysis showed that at the intermediate gap flow regime the large scale vortices have been bowed and deformed by the vorticity created by the presence of the wall, their formation location was moved downstream as the gap-to-diameter ratio was decreased. At the small gap flow regime the instantaneous flow fields and the POD results revealed the existence of large scale vortices shed from the upper shear layer (other than Von Kármán vortices). The streamline plots showed that the flow structure at this gap regime is identical to the structure of the flow behind a back-step. Phase averaged flow fields showed that the location of the jet-like flow “axis” depended on the upper shear layer vortices formation cycle. In fact, the jet-like flow took different “incident” angles and different downstream locations at different phase instants during the formation of the upper shear layer vortices.

Role of preoperative 3D CT reconstruction for evaluation of patients with esophageal atresia and tracheoesophageal fistula

The role of preoperative contrast-enhanced computerized tomography (CT) of chest with three-dimensional (3D) reconstructions was evaluated in neonates with esophageal atresia and tracheoesophageal fistula. This was a prospective study which investigated 30 cases of esophageal atresia with tracheoesophageal fistula. All patients were evaluated preoperatively with contrast-enhanced spiral CT using a low-dose CT protocol. 3D CT reconstruction images were evaluated for the type of esophageal atresia, the distance between the upper and lower esophageal pouches, origin, level and position of the fistula, and the presence or absence of any other cardiac, pulmonary or mediastinal lesions and the findings were correlated with the findings at surgery. The radiation dose for each patient was calculated using the formula-Effective dose (E) = DLP × (E/DLP)age. All the 30 cases had type-C esophageal atresia with tracheoesophageal fistula as per Gross classification. The exact site of the fistula could be identified only in 26 (80 %) cases. The mean gap between the upper pouch and lower fistula was 0.95 ± 0.57 cm (range 0.2-2.8 cm) on CT scan and 1.38 ± 0.61 cm (range 0.5-3.2 cm) at surgery. On statistical analysis, the correlation was found to be significant (p < 0.0001). In addition, lung pathology (consolidation), cardiac pathology and vertebral anomaly were also detected on CT scan in some cases. The mean radiation dose for the neonates who underwent CT chest was calculated to be 1.79 mSv which is significantly high. Though preoperative CT scan of chest has many advantages, it involves significant exposure to ionizing radiation and risk of radiation-induced cancer in the future. Additionally in 20 % of cases, the fistula could not be located on CT scan. The most common variety of esophageal atresia and tracheoesophageal fistula is Gross type C (86 %) that has low to intermediate gap (97 %) and can be anastomosed primarily. Thus, CT scan can provide good anatomical delineation, but may not help in surgical decision making. Hence, performing CT in these cases would unnecessarily expose the neonates to ionizing radiation. Therefore, there is no role for CT scan in the routine preoperative assessment of EA with distal TEF.

Do deer and shrubs override canopy gap size effects on growth and survival of yellow birch, northern red oak, eastern white pine, and eastern hemlock seedlings?

Innovative forestry practices that use natural disturbance and stand developmental processes as models to increase forest complexity are now being considered as a way to conserve biodiversity while managing for a range of objectives. We evaluated the influence of harvest-created gap size (6, 10, 20, 30, and 46m diameter gaps and uncut references) over 12 growing seasons on planted tree seedling growth and survival for four tree species that tend to experience poor recruitment in both managed and unmanaged northern hardwood forests in eastern North America. We expected, based on silvics, that the three mid-tolerant species (yellow birch [Betula alleghaniensis], red oak [Quercus rubra], and white pine [Pinus strobus]) would perform best in intermediate-sized gaps, and the one shade tolerant species (hemlock [Tsuga canadensis]) would perform best in small gaps. However, all four of the species grew taller with increasing gap size, while survival was highest in intermediate gap sizes. Although gap size had statistically significant effects on growth and survival, the magnitude of the effects were modest. With the exception of a small portion of white pine individuals (35% of survivors were >150cm tall), trees were short (<1m) and few survived (<30%) 12years after planting. Evidence from deer exclosures and individual gaps with high shrub (Rubus idaeus) densities suggest that browsing and shrub competition resulted in poor tree growth and survival, and may have constrained the magnitude of many potential tree seedling responses to gap size. Our study highlights the management challenges of using gap size as a tool to influence future forest composition in forests with overly abundant deer and pervasive shrub layers and underscores the importance of silvicultural prescriptions that include measures for reducing these impacts.

Cavitation bubble dynamics in a liquid gap of variable height

We report on an experimental study of cavitation bubble dynamics within sub-millimetre-sized narrow gaps. The gap height is varied, while the position of the cavitation event is fixed with respect to the lower gap wall. Four different sizes of laser-induced cavitation bubbles are studied using high-speed photography of up to 430,000 frames per second. We find a strong influence of the gap height, H, on the bubble dynamics, in particular on the collapse scenario. Also, similar bubble dynamics was found for the same non-dimensional gap height η = H/Rx, where Rx is the maximum radius in the horizontal direction. Three scenarios are observed: neutral collapse at the gap centre, collapse onto the lower wall and collapse onto the upper wall. For intermediate gap height the bubble obtains a conical shape 1.4 &lt; η &lt; 7.0. For large distances, η &gt; 7.0, the bubble no longer feels the presence of the upper wall and collapses hemispherically. The collapse time increases with respect to the expansion time for decreasing values of η. Due to the small scales involved, the final stage of the bubble collapse could not be resolved temporally and numerical simulations were performed to elucidate the details of the flow. The simulations demonstrate high-speed jetting towards the upper and lower walls and complex bubble splitting for neutral collapses.

The interaction of gap age and microsite for herb layer species in a near-natural spruce forest

Question: To what degree does the regeneration of understorey forest species depend on gaps of different age and on gap-induced and non-gap-induced microsites? Do species preferences for a specific microsite change with the developmental stage of the gap? How do different species in the understorey interact over time? Location: Near-natural spruce forest on Mt. Brocken in the Harz National Park, Germany. Methods: We established 90 study plots, stratified according to different gap age classes and undisturbed forest, and including subplots with three different gap-induced types of microsites (logs, stumps and root plates) and two non-gap-induced microsites (moss-covered rocks and ordinary forest ground). Results: Significant interactions of species were encountered with gap age as well as with microsite type, light availability and competition. While shoot densities of Vaccinium myrtillus were highest at intermediate gap age, Calamagrostis villosa and Trientalis europaea showed highest densities in the oldest gaps. The species preferred different microsites but had higher densities on non-gap-induced microsites, and their preferences changed over time. Unexpectedly, species shoot densities were not always negatively affected by densities of competing species. Conclusion: The results confirmed the importance of gaps for regeneration of forest herb layer species, but pointed to a much higher importance of microsites that were not induced by gaps compared to gap-induced microsites. Niche differentiation between different herb layer species can be conceived as species-specific preferences for microsite types that change with gap age, as a result of light conditions, degree of decay of logs and root plates and presence of competitors.

변형된 원형 버섯 구조의 0차 공진을 이용한 메타 재질 대역 통과 여파기의 설계

본 논문에서는 변형된 원형 버섯 구조의 메타 재질을 이용하여 새로운 대역 통과 여파기의 설계법을 제안한다. 0차 공진(Zeroth-Order Resonance: ZOR) 특성을 보이는 반원 형태의 버섯 구조 셀을 공진기로 이용하며, 각각의 이웃하는 0차 공진기 사이에 갭을 두어 용량성 결합을 유도한다. 제안된 메타 재질 대역 통과 여파기 설계법은 회로 해석 및 3차원 모의 실험과 측정을 통하여 해석 및 설계 목표와 비교 분석되어 그 타당성을 증명하였다. 0차 공진의 특수한 전계 분포 및 분산도를 통하여 메타 재질임을 증명하였으며, 대역 통과 여파기의 소형화에 대하여도 논의된다. In this paper, the design of a new bandpass filter based on the modified circular mushroom metamaterial structure is proposed. In detail, half circular mushroom cells are used as the zeroth order resonators(ZOR), and an intermediate gap is adopted to introduce the coupling between neighboring ZOR resonators. The proposed bandpass filter design is validated by the circuit and 3D EM simulations and measurements compared to the target specifications, and the metamaterial properties are proved by the ZOR field distributions and dispersion diagram. Also, the effect of size reduction is addressed.

Triarylmethane‐34 (TRAM‐34), inhibitor of Ca2+‐activated K+ channels of intermediate conductance, is a potent blocker of gap junctions

Ca2+‐activated K+ channels of intermediate conductance (IKCa) and gap junctions (GJs) between endothelial and smooth muscle cells have been proposed to play a central role in the vasodilator response mediated by the endothelium‐derived hyperpolarizing factor (EDHF). Although TRAM‐34, the IKCa channels blocker, has emerged as an important pharmacological tool for studying EDHF‐mediated responses, its effect on GJs has not been described. We analyzed intercellular communication and cellular distribution of the GJ protein subunit, connexins (Cxs), in HeLa cells transfected with Cx43 or Cx43 conjugated to EGFP. Treatment with 10μM TRAM‐34 induced a time dependent reduction in dye coupling to Lucifer yellow; the average number of coupled cells observed in positive tests was reduced by ~50% after 20 min and abolished after 70 min. Dye coupling was recovered to control 30 min after TRAM‐34 wash out. The reduction in GJ communication was not associated with changes in levels or distribution of Cx43‐EGFP. Therefore, TRAM‐34, in addition to inhibit IKCa channels, also potently blocks the cell‐to‐cell communication mediated by the GJ protein Cx43 that is an important connexin involved in the coordination of resistance vessel function.VRAID 15/2009, FONDEF D07I1086.

Effects of frequency ratio on bridge aerodynamics determined by free-decay sectional model tests

A series of wind tunnel free-decay sectional model dynamic tests were conducted to examine the effects of torsional-to-vertical natural frequency ratio of 2DOF bridge dynamic systems on the aerodynamic and dynamic properties of bridge decks. The natural frequency ratios tested were around 2.2:1 and 1.2:1 respectively, with the fundamental vertical natural frequency of the system held constant for all the tests. Three 2.9 m long twin-deck bridge sectional models, with a zero, 16% (intermediate gap) and 35% (large gap) gap-to-width ratio, respectively, were tested to determine whether the effects of frequency ratio are dependent on bridge deck cross-section shapes. The results of wind tunnel tests suggest that for the model with a zero gap-width, a model to approximate a thin flat plate, the flutter derivatives, and consequently the aerodynamic forces, are relatively independent of the torsional-to-vertical frequency ratio for a relatively large range of reduced wind velocities, while for the models with an intermediate gap-width (around 16%) and a large gap-width (around 35%), some of the flutter derivatives, and therefore the aerodynamic forces, are evidently dependent on the frequency ratio for most of the tested reduced velocities. A comparison of the modal damping ratios also suggests that the torsional damping ratio is much more sensitive to the frequency ratio, especially for the two models with nonzero gap (16% and 35% gap-width). The test results clearly show that the effects of the frequency ratio on the flutter derivatives and the aerodynamic forces were dependent on the aerodynamic cross-section shape of the bridge deck.

Electron Spin Relaxation Due to Phonon Modulation of the Rashba Interaction in Quantum Dots

In this work we calculate the spin-flip transition rates, considering the phonon modulation of the spin–orbit interaction. For this purpose will use the spin–phonon interaction Hamiltonian proposed by Pavlov and Firsov. We compare the contributions of the electron–phonon deformation potential (DP) and piezoelectric (PE) coupling to the spin relaxation. We reveal the importance of an appropriate description of the electron Lande g-factor in the calculation of the rates. Our results demonstrate that, for narrow-gap materials, the DP interaction becomes the dominant one. This behavior is not observed in wide or intermediate gap semiconductors, where the PE coupling, in general, governs the relaxation processes.

Cell contacts in the mouse mammary gland

The nature and distribution of cell contacts have been examined in thin sections and freeze-fracture replicas of mammary gland samples from female C3H/Crgl mice at stages from birth through pregnancy, lactation, and postweaning involution. Epithelial cells of major mammary ducts at all stages examined are linked at their luminal borders by junctional complexes consisting of tight junctions, variable intermediate junctions, occasional small gap junctions, and one or more series of desmosomes. Scattered desmosomes and gap junctions link ductal epithelial and myoepithelial cells in all combinations; hemidesmosomes attach myoepithelial cells to the basal lamina. Freeze-fracture replicas confirm the erratic distribution of gap junctions and reveal a loose, irregular network of ridges comprising the continuous tight-junctional belts. Alveoli develop early in gestation and initially resemble ducts. Later, as alveoli and small ducts become actively secretory, they lose all desmosomes and most intermediate junctions, whereas tight and gap junctions persist, The tight-junctional network becomes compact and orderly, its undulating ridges oriented predominantly parallel to the luminal surface. It is suggested that these changes in junctional morphology, occurring in secretory cells around parturition, may" be related to the greatly enhanced rate of movement of milk precursors and products tbrough the lactating epithelium, or to the profound and recurrent changes in shape of secretory cells that occur in relation to myoepithelial cell contraction, or to both.

Spin relaxation rates in quantum dots: Role of the phonon modulated spin–orbit interaction

We calculate the spin relaxation rates in InAs and GaAs parabolic quantum dots due to the interaction of spin carriers with acoustical phonons. We consider a spin relaxation mechanism completely intrinsic to the system, since it is based on the modulation of the spin–orbit interaction by the acoustic phonon potential, which is independent of any structural properties of the confinement potential. The electron–phonon deformation potential and the piezoelectric interaction are described by the Pavlov–Firsov spin–phonon Hamiltonian. Our results demonstrate that, for narrow-gap semiconductors, the deformation potential interaction becomes dominant. This behavior is not observed for wide or intermediate gap semiconductors, where the piezoelectric coupling, in general, governs the relaxation processes. We also demonstrate that the spin relaxation rates are particularly sensitive to values of the Landé g -factor, which depend strongly on the spatial shape of the confinement.

The Coulomb gap and low energy statistics for Coulomb glasses

We study the statistics of local energy minima in the configuration space oftwo-dimensional lattice Coulomb glasses with site disorder and the behavior of theCoulomb gap depending on the strength of random site energies. At intermediatedisorder, i.e., when the typical strength of the disorder is of the same order as thenearest-neighbor Coulomb energy, the high energy tail of the distribution of the localminima is exponential. We furthermore analyze the structure of the local minima andshow that most sites of the system have the same occupation numbers in all ofthese states. The density of states (DOS) shows a transition from the crystallinestate at zero disorder (with a hard gap) to an intermediate, probably glassy statewith a Coulomb gap. We analyze this Coulomb gap in some detail and showthat the DOS deviates slightly from the traditional linear behavior in 2D. Forfinite systems these intermediate Coulomb gap states disappear for large disorderstrengths and only a random localized state in which all electrons are in the minimaof the random potential exists.Dedication: This paper is dedicated to ThomasNattermann, our dearest friend, brilliant colleague, and outstanding teacher.