Topology induced anomalous defect production by crossing a quantum critical point

We study the influence of topology on the quench dynamics of a system driven across a quantum critical point. We show how the appearance of certain edge states, which fully characterise the topology of the system, dramatically modifies the process of defect production during the crossing of the critical point. Interestingly enough, the density of defects is no longer described by the Kibble-Zurek scaling, but determined instead by the non-universal topological features of the system. Edge states are shown to be robust against defect production, which highlights their topological nature.Comment: Phys. Rev. Lett. (to be published

Optical imaging of resonant electrical carrier injection into individual quantum dots

We image the micro-electroluminescence (EL) spectra of self-assembled InAs quantum dots (QDs) embedded in the intrinsic region of a GaAs p-i-n diode and demonstrate optical detection of resonant carrier injection into a single QD. Resonant tunneling of electrons and holes into the QDs at bias voltages below the flat-band condition leads to sharp EL lines characteristic of individual QDs, accompanied by a spatial fragmentation of the surface EL emission into small and discrete light- emitting areas, each with its own spectral fingerprint and Stark shift. We explain this behavior in terms of Coulomb interaction effects and the selective excitation of a small number of QDs within the ensemble due to preferential resonant tunneling paths for carriers.Comment: 4 page

Topology induced anomalous defect production by crossing a quantum critical point

We study the influence of topology on the quench dynamics of a system driven across a quantum critical point. We show how the appearance of certain edge states, which fully characterise the topology of the system, dramatically modifies the process of defect production during the crossing of the critical point. Interestingly enough, the density of defects is no longer described by the Kibble-Zurek scaling, but determined instead by the non-universal topological features of the system. Edge states are shown to be robust against defect production, which highlights their topological nature.Comment: Phys. Rev. Lett. (to be published

Controlling high-frequency collective electron dynamics via single-particle complexity

We demonstrate, through experiment and theory, enhanced high-frequency current oscillations due to magnetically-induced conduction resonances in superlattices. Strong increase in the ac power originates from complex single-electron dynamics, characterized by abrupt resonant transitions between unbound and localized trajectories, which trigger and shape propagating charge domains. Our data demonstrate that external fields can tune the collective behavior of quantum particles by imprinting configurable patterns in the single-particle classical phase space.Comment: 5 pages, 4 figure

Entanglement crossover close to a quantum critical point

We discuss the thermal entanglement close to a quantum phase transition by analyzing the concurrence for one dimensional models in the quantum Ising universality class. We demonstrate that the entanglement sensitivity to thermal and to quantum fluctuations obeys universal $T\neq 0$--scaling behaviour. We show that the entanglement, together with its criticality, exhibits a peculiar universal crossover behaviour.Comment: 12 pages; 5 figures (eps). References added; to be published in Europhysics Letter

Excitonic mobility edge and ultra-short photoluminescence decay time in n-type GaAsN

We use time-resolved photoluminescence (PL) spectroscopy to study the recombination dynamics in Si-doped GaAsN semiconductor alloys with a nitrogen content up to 0.2%. The PL decay is predominantly monoexponential and exhibits a strong energy dispersion. We find ultra-short decay times on the high-energy side and long decay times on the low-energy side of the photoluminescence spectrum. This asymmetry can be explained by the existence of an additional non-radiative energy transfer channel and is consistent with previous studies on intrinsic GaAsN epilayers. However, the determined maximum decay times of GaAsN:Si are significantly reduced in comparison to undoped GaAsN. The determined excitonic mobility edge energy constantly decreases with an increase in the N content, in agreement with the two-level band anticrossing model

Polarization-modulation near-field optical microscope for quantitative local dichroism mapping

A couple of experimental techniques have been implemented to an aperture near-field scanning optical microscopy (NSOM) to obtain reliable measurement of sample dichroism on the local scale. First, a method to test NSOM tapered fiber probes toward polarization conservation into the near optical field is reported. The probes are characterized in terms of the in-plane polarization of the near field emerging from their aperture, by using a thin dichroic layer of chromophore molecules, structured along stretched polymeric chains, to probe such polarization when approached in the near-field region of the probe. Second, to assure that the light intensity coupled in the fiber is polarization independent, an active system operating in real time has been realized. Such combination of techniques allowed quantitative imaging of local dichroism degree and average orientation by means of dual-phase lock-in demodulation of the optical signal. Translation of the coupled light polarization state in the near field has been observed for one-half of the tested probes. For the others, the tip acts as a polarizer, and therefore showed it was not suitable for polarization modulation NSOM measurements

Organic μ cavities based on thermally evaporated TeOx-LiF distributed Bragg reflectors

We report on the realization of high-quality organic microcavities consisting of distributed Bragg reflectors based on lithium fluoride (LiF) and tellurium dioxide (TeOx) deposited by thermal evaporation. The materials are transparent in the range of 350 nm-5 mum and have an evaporation temperature of about 1000 K. The large difference in the refractive index (about 0.9 in the visible and near-infrared range) allows one to obtain reflectivity higher than 99% over a spectral region about 200 nm wide with a small number of periods. The mirror deposition technique is suitable for the fabrication of organic quantum microcavities in a single deposition process. Three fully evaporated organic lambda cavities with Phyrrometene 580 as the active material are described. The cavities show a Q value of up to 300, good uniformity, and reproducibility

Time evolution of methotrexate-induced kidney injury: A comparative study between different biomarkers of renal damage in rats

Methotrexate (MTX) is commonly used in the treatment of malignant diseases and autoimmune and chronic inflammatory disorders. Along with its effective therapeutic power, MTX has adverse effects on the kidneys. Discovery of new biomarkers is required to improve the early detection of renal damage and optimize the effectiveness of treatments. The aim of this study was to evaluate the time course of MTX-induced nephrotoxicity and to compare the urinary excretion of the organic anion transporter 5 (uOat5) with alterations in other markers of renal function, and to elucidate the possible molecular mechanisms involved in uOat5. Animals were exposed to a unique dose of MTX (80 mg/kg body weight, intraperitoneal). Experiments were carried out at days 2, 4, 8 or 14 after MTX administration. Markers of renal damage, such as creatinine and urea plasma levels, urinary activity of alkaline phosphatase, microalbuminuria, urinary excretion of neutrophil gelatinase-associated lipocalin (uNGAL) and histopathology, were evaluated. Renal organic anion transporter 5 (Oat5) expression and its presence in different urine fraction were assessed by western blotting. uOat5 was significantly increased 2 days after MTX treatment, before than any alteration in other parameters of kidney injury or renal morphology occurred. uNGAL showed an inverted pattern of urinary excretion compared to uOat5. Exosomal pathway is involved in the urinary excretion of Oat5 and depends on the degree of damage induced by MTX. These experimental data allow proposing uOat5 as a potential non-invasive biomarker for early detection of MTX-induced nephrotoxicity.Fil: Severin, María Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmaceuticas. Departamento de Ciencias Fisiológicas. Area Farmacología; ArgentinaFil: Campagno, Romina Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmaceuticas. Departamento de Ciencias Fisiológicas. Area Farmacología; ArgentinaFil: Brandoni, Anabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmaceuticas. Departamento de Ciencias Fisiológicas. Area Farmacología; ArgentinaFil: Torres, Adriana Mónica. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmaceuticas. Departamento de Ciencias Fisiológicas. Area Farmacología; Argentin