Excitonic instabilities and spontaneous time-reversal symmetry breaking on the honeycomb lattice

We elucidate the close relationship between spontaneous time-reversal symmetry breaking and the physics of excitonic instabilities in strongly correlated multiband systems. The underlying mechanism responsible for the spontaneous breaking of time-reversal symmetry in a many-body system is closely related to the Cooper-like pairing instability of interband particle-hole pairs involving higher-order symmetries. Studies of such pairing instabilities have, however, mainly focused on the mean-field aspects of the virtual exciton condensate, which ignores the presence of the underlying collective Fermi-liquid excitations. We show that this relationship can be exploited to systematically derive the coupling of the condensate order parameter to the intraband Fermi-liquid particle-hole excitations. Surprisingly, we find that the static susceptibility is negative in the ordered phase when the coupling to the Fermi-liquid collective excitations are included, suggesting that a uniform condensate of virtual excitons, with or without time-reversal breaking, is an unstable phase at T = 0.

Methods and results of a search for gravitational waves associated with gamma-ray bursts using the GEO 600, LIGO, and Virgo detectors

In this paper we report on a search for short-duration gravitational wave bursts in the frequency range 64 Hz-1792 Hz associated with gamma-ray bursts (GRBs), using data from GEO 600 and one of the LIGO or Virgo detectors. We introduce the method of a linear search grid to analyze GRB events with large sky localization uncertainties, for example the localizations provided by the Fermi Gamma-ray Burst Monitor (GBM). Coherent searches for gravitational waves (GWs) can be computationally intensive when the GRB sky position is not well localized, due to the corrections required for the difference in arrival time between detectors. Using a linear search grid we are able to reduce the computational cost of the analysis by a factor of O(10) for GBM events. Furthermore, we demonstrate that our analysis pipeline can improve upon the sky localization of GRBs detected by the GBM, if a high-frequency GW signal is observed in coincidence. We use the method of the linear grid in a search for GWs associated with 129 GRBs observed satellite-based gamma-ray experiments between 2006 and 2011. The GRBs in our sample had not been previously analyzed for GW counterparts. A fraction of our GRB events are analyzed using data from GEO 600 while the detector was using squeezed-light states to improve its sensitivity; this is the first search for GWs using data from a squeezed-light interferometric observatory. We find no evidence for GW signals, either with any individual GRB in this sample or with the population as a whole. For each GRB we place lower bounds on the distance to the progenitor, under an assumption of a fixed GW emission energy of 10(-2)M circle dot c(2), with a median exclusion distance of 0.8 Mpc for emission at 500 Hz and 0.3 Mpc at 1 kHz. The reduced computational cost associated with a linear search grid will enable rapid searches for GWs associated with Fermi GBM events once the advanced LIGO and Virgo detectors begin operation.

A theoretical characterization of scaling properties in a bouncing ball system

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Graphene sheet versus two-dimensional electron gas: A relativistic Fano spin filter via STM and AFM tips

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fano interference and a slight fluctuation of the Majorana hallmark

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measuring Quantum Capacitance in Energetically Addressable Molecular Layers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Disorder induced interface states and their influence on the AI/Ge nanowires Schottky devices

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Subtle leakage of a Majorana mode into a quantum dot

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Release of Cyanopyridine from a Ruthenium Complex Adsorbed on Gold: Surface-Enhanced Raman Scattering, Electrochemistry, and Density Functional Theory Analyses

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Probing the antisymmetric Fano interference assisted by a Majorana fermion

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Separation of particles leading either to decay or unlimited growth of energy in a driven stadium-like billiard

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Spin-dependent beating patterns in thermoelectric properties: Filtering the carriers of the heat flux in a Kondo adatom system

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Desenvolvimento de tratamentos térmicos visando ganhos magnéticos em aços com ultra baixa concentração de carbono

The relationship between the microstructure and the magnetic properties of soft magnetic materials, have been studied by different researchers who seek to employ electrical systems, increasing their life span and reduce their energy consumption. Following this same line the Brazilian Synchrotron Light Laboratory developed a new synchrotron light source, the Sirius, where magnetic materials with high magnetic permeability values are being studied for use in accelerator dipoles. The low carbon steel is a ferromagnetic material that has a great relationship between cost and magnetic permeability. Aiming to raise the values of permeability of the material, heat treatments were done and evaluated the magnetic properties, microstructure and mechanical properties to correlate them. It was noted that the thermal annealing were the most effective, and the annealing performed with a small time threshold, which only phenomenon observed was the primary recrystallisation, was the most elevated values of magnetic permeability of the material, due to the average grain size ideal achieved. The heat treatments do not guide the magnetic domains of the material and not influence the mechanical properties of the material due to lack of carbon in the microstructure. The annealing treatments were shown to be an alternative to raising the values of the magnetic permeability of the material and facilitate the implementation of ultra low carbon steel in the dipoles of Sirius

Radioterapia com elétrons

Radiotherapy is a field of medical physics, which has been going through a scientific and technological advancement, it is extreme important the professionals that work in this area continuous their study to improve the quality of service provided. For it, they should know the physical principles related as well their employment in radiotherapy. The electrons have been using in therapy of superficial tumors, because they show rapid decrease of dose in depth, they don’t expose the deeper tissues to radiation. The electron therapy has replaced the surface therapy with x-ray and mold brachytherapy, and nowadays, it represents 10 to 15% of radiotherapy treatments. This study brings the definition of physical parameters used in the dosimetry of electron beam, describes the tests for quality control of linear accelerator with a electrons beam, as well the activities realized in the Radiotherapy Division, of Hospital de Clinicas, in the Universidade Estadual of Campinas, in the Clinac 2100C machine

Efeitos de campos elétrico e magnético em um sistema dissipativo pulsante

The main idea of this work is to understand and analyze the dynamical aspects of the motion of a particle moving in the annular billiard, which corresponds to two circles of radius R and r (rdescribe the system by introducing breathing boundaries that transfer momentum to the particle. Likewise, the collisions with the circles are studied in the conservative (elastic) and dissipative (non-elastic) cases. When we introduce magnetic and electric fields, the particle is submitted to the Lorentz force. It also can suffer successive collisions with the breathing circles, winning or losing energy. For the elastic time-dependent case, we have already observed that a particle can gain unlimited energy. The purpose of this work is to study the effects of both external fields in the mean energy of the system, for the time-dependent case with and without dissipation. Our initial results conduct us to believe that electrical field can contribute to the increasing of mean energy, and a magnetic field applied to the vertical axis of coordinate (what guarantees the particle do not travel away the billiard’s plane) uses to arrest the particle to the whispering gallery orbits and do not contribute to the Fermi acceleration indeed. However, in presence of the electric field, to same values, the magnetic one together can improve this referred process, obtaining greater energy values to the same number of iterations. These results are applied to the concentric case, that was reported did not haven any significant energy gain on the free particle motion