Phonon Bloch oscillations in acoustic-cavity structures

We describe a semiconductor multilayer structure based in acoustic phonon cavities and achievable with MBE technology, designed to display acoustic phonon Bloch oscillations. We show that forward and backscattering Raman spectra give a direct measure of the created phononic Wannier-Stark ladder. We also discuss the use of femtosecond laser impulsions for the generation and direct probe of the induced phonon Bloch oscillations. We propose a gedanken experiment based in an integrated phonon source-structure-detector device, and we present calculations of pump and probe time dependent optical reflectivity that evidence temporal beatings in agreement with the Wannier-Stark ladder energy splitting.Comment: PDF file including 4 figure

Optical cavity mode dynamics and coherent phonon generation in high-Q micropillar resonators

International audienceWe study the temporal dynamics of photoexcited carriers in distributed Bragg reflector based semiconductor micropillars at room temperature. Their influence on the process of coherent phonon generation and detection is analyzed by means of pump-probe microscopy. The dependence of the measured mechanical signatures on laser-cavity detuning is explained through a model that accounts for the varying light-cavity coupling existent during the ultrashort times that pump and probe pulses dwell within the structure. To do so, we first explain the optical mode dynamics with an electron-hole diffusion model that accounts for the escape of carriers from the probed area, as well as their recombination in the bulk and on the free surfaces. We thus show that the latter is the most influential factor for pillars below ∼10μm, where 3D confinement of the optical and mechanical fields becomes relevant

Uncoupled excitons in semiconductor microcavities detected in resonant Raman scattering

We present an outgoing resonant Raman-scattering study of a GaAs/AlGaAs based microcavity embedded in a p-i-n junction. The p-i-n junction allows the vertical electric field to be varied, permitting control of exciton-photon detuning and quenching of photoluminescence which otherwise obscures the inelastic light scattering signals. Peaks corresponding to the upper and lower polariton branches are observed in the resonant Raman cross sections, along with a third peak at the energy of uncoupled excitons. This third peak, attributed to disorder activated Raman scattering, provides clear evidence for the existence of uncoupled exciton reservoir states in microcavities in the strong-coupling regime

Scaling rules in optomechanical semiconductor micropillars

International audienceSemiconductor pillar microcavities have recently emerged as a promising optomechanical platform in the unprecedented 20-GHz frequency range. Currently established models for the mechanical behavior of micropillars, however, rely on complete numerical simulations or semianalytical approaches, which makes their application to experiments notoriously difficult. Here we overcome this challenge with an effective model by reducing the full, hybridized mechanical mode picture of a micropillar to an approach that captures the observed global trends. We show experimentally the validity of this approach by studying the lateral size dependence of the frequency, amplitude, and lifetime of the mechanical modes of square-section pillar microcavities, using room-temperature pump-probe microscopy. General scaling rules for these quantities are found and explained through simple phenomenological models of the physical phenomena involved. We show that the energy shift ω m of the modes due to confinement is dependent on the inverse of their frequency ω 0 and lateral size L (ω m ∝ 1/ω 0 L 2) and that the mode lifetime τ is linear with pillar size and inversely proportional to their frequency (τ ∝ L/ω 0). The mode amplitude is in turn inversely proportional to the lateral size of the considered resonators. This is related to the dependence of the optomechanical coupling rate (g 0 ∝ 1/L) with the spatial extent of the confined electromagnetic and mechanical fields. Using a numerical model based on the finite-element method, we determine the magnitude and size dependence of g 0 and, by combining the results with the experimental data, we discuss the attainable single-photon cooperativity in these systems. The effective models proposed and the scaling rules found constitute an important tool in micropillar optomechanics and in the future development of more complex micropillar based devices

Structural analysis, magnetic and transport properties of the (Ru1-xCox)Sr2GdCu2O8 system

The effects of Co substitution on structural and superconducting properties of RuSr2GdCu2O8 compound have been studied. Rietveld refinements of the X-ray diffraction patterns indicate that the cobalt ion progressively replaces ruthenium sites. This replacement induces significant changes on the crystal structure and on the magnetic and superconducting properties. The effects Co substitution on the superconducting behaviour, and more particulary on the changes induce by the hole doping mechanism, were investigated in (Ru1-xCox)Sr2GdCu2O8 by a "bond valence sum" analysis with Co content from x= 0.0 to x = 0.2. The weak ferromagnetic transition at Tm= 138.2 K is shifted to lower temperature, and suppressed at higher Co content. From the crystallographic point of view the Ru-O(1)-Cu bond angle, associated to the rotation of the RuO6 octahedra, around the c-axis remain essetially constant when Ru is substituted by Co. Furthermore, increasing Co content has the effect to increase the weak ferromagnetic moment, which may be interpreted as the main responsible for breaking the delicate balance between magnetic and superconducting ordering.Comment: 21 pages, 8 figure

Scaling and Formulary cross sections for ion-atom impact ionization

The values of ion-atom ionization cross sections are frequently needed for many applications that utilize the propagation of fast ions through matter. When experimental data and theoretical calculations are not available, approximate formulas are frequently used. This paper briefly summarizes the most important theoretical results and approaches to cross section calculations in order to place the discussion in historical perspective and offer a concise introduction to the topic. Based on experimental data and theoretical predictions, a new fit for ionization cross sections is proposed. The range of validity and accuracy of several frequently used approximations (classical trajectory, the Born approximation, and so forth) are discussed using, as examples, the ionization cross sections of hydrogen and helium atoms by various fully stripped ions.Comment: 46 pages, 8 figure

Decoupled CuO_2 and RuO_2 layers in superconducting and magnetically ordered RuSr_2GdCu_2O_8

Comprehensive measurements of dc and ac susceptibility, dc resistance, magnetoresistance, Hall resistivity, and microwave absorption and dispersion in fields up to 8 T have been carried out on RuSr_2GdCu_2O_8 with the aim to establish the properties of RuO_2 and CuO_2 planes. At ~130 K, where the magnetic order develops in the RuO_2 planes, one observes a change in the slope of dc resistance, change in the sign of magnetoresistance, and the appearance of an extraordinary Hall effect. These features indicate that the RuO_2 planes are conducting. A detailed analysis of the ac susceptibility and microwave data on both, ceramic and powder samples show that the penetration depth remains frequency dependent and larger than the London penetration depth even at low temperatures. We conclude that the conductivity in the RuO_2 planes remains normal even when superconducting order is developed in the CuO_2 planes below \~45 K. Thus, experimental evidence is provided in support of theoretical models which base the coexistence of superconductivity and magnetic order on decoupled CuO_2 and RuO_2 planes.Comment: 11 pages, 11 figures, submitted to PR

Competing Ideas of Social Justice and Space: Locating Critiques of Housing Renewal in Theory and in Practice

This article considers the experience of the English government's policy of Housing Market Renewal from the perspective of spatial justice. The paper first proposes an analytical framework that situates competing notions of territorial social justice within a space of complex sociospatial relations. The dialectic of two formulations of social justice is first set up, comparing 'procedural' or deontological forms of justice and the distributional justice of outcomes. Soja's formulation of spatial justice is advanced as an appropriate balance between spatial and socio-historic contexts for the justice question. Drawing on the literature on sociospatial relations, concrete critiques and justifications of HMR are then positioned in terms of the intersection of structuring principles and policy fields. The role of demolition in urban restructuring programmes is used to explore the differential spatialities involved in different justicial perspectives. It is concluded that 'gentrification' critiques of HMR are only partial in their evaluation of justice and lack normative power. Some practical implications for the design of urban restructuring policies are offered

Наследственный лейомиоматоз и почечноклеточный рак: клинический случай

This article presents a case report of hereditary leiomyomatosis and renal cell cancer (HLRCC) with new mutation in a 25-year-old female patient admitted to the clinic for diagnosis and treatment due to multiple skin and uterus leiomyomas. The patient has a history of surgery to remove adrenal pheochromocytoma and papillary kidney cancer. Clinical and laboratory examination as well as medical genetic counseling of the patient were performed. We have detected the heterozygous c.395_399del (p.L132*) germline nonsense mutation in exon 4 of the FH gene using polymerase chain reaction/Sanger sequencing of exons 1–10 of this gene and confirmed the diagnosis of HLRCC. The mutation c.395_399del in a patient with HLRCC was described for the first time. The identical mutation was also found in the mother and sister of the patient. Based on the obtained results, medical genetic counseling was carried out in this family, recommendations were given for further oncological monitoring. The case report could be useful for geneticists, oncologists and other specialists to interpretate the clinical heterogeneity of HLRCC and improve the genetic diagnosis of this rare hereditary oncological syndrome.В настоящей работе представлено описание клинического случая наследственного лейомиоматоза и почечно-клеточного рака (hereditary leiomyomatosis and renal cell cancer, HLRCC) с новой мутацией у пациентки 25 лет, поступившей в клинику для диагностики и лечения в связи с множественными лейомиомами кожи и матки. В анамнезе  у пациентки операции по удалению феохромоцитомы надпочечника и папиллярного рака почки. Проведены клинико-лабораторное обследование и медико-генетическое консультирование пациентки. Полимеразная цепная реакция и секвенирование по Сэнгеру экзонов 1–10 гена FН в ДНК из крови позволили выявить в экзоне 4 нонсенс-мутацию с.395_399del (p.L132*) в гетерозиготном состоянии и тем самым подтвердить диагноз HLRCC. Герминальная мутация с.395_399del у пациента с HLRCC описана нами впервые. Идентичная мутация выявлена у матери и сестры пациентки. По совокупности полученных результатов в семье проведено медико-генетическое консультирование, даны рекомендации по дальнейшему наблюдению. Описанный нами случай может помочь генетикам, онкологам и другим специалистам ориентироваться в клинической гетерогенности HLRCC и генетической диагностике этого редкого наследственного онкологического синдрома