Condensed Matter Physics (Theory and Experimental)

In Condensed Matter works are developed in the following lines of research:

Magnetic and Magnetocaloric Properties in Metallic Compounds

The magnetocaloric effect (EMC) occurs when a magnetic material is placed inside a magnetic field and a change in the temperature of the magnetic material is observed. In ferromagnetic materials the temperature increases when it is placed in a magnetic field and decreases when withdrawn from the magnetic field in an adiabatic process (i.e. without heat exchange). The EMC can be used in magnetic refrigeration and this makes it very attractive from the point of view of technological application. Conventional refrigerators used today in industries, commercial houses and homes use as a refrigerant material a gas typically CFC and HCFC. These gases, however, are identified as the main responsible for the destruction of the ozone layer in the atmosphere, which protects us from the ultraviolet radiation produced by the Sun. Unlike the magnetic refrigerator makes use of (as a refrigerant) the use of the polluting gases and, in addition, produces refrigeration with less loss of energy.

In this line of research we study from the theoretical point of view the magnetic, thermodynamic and magnetocaloric effects in pure and disordered metallic systems. In particular we are interested in the effect of the external magnetic field pressure, the crystalline electric field on the magnetic and magnetocaloric properties of systems with first order phase transition. Theoretical calculations are based on interagent spins models where spin-spin interaction is treated in the midfield approximation or Monte Carlo simulation.

Semiconductor Nanostructures

The possibility of building ever smaller devices gave us access to the scale of systems with nanometric dimensions (1nm = 10-9m). In this scale we observe typical quantum behaviors for the electrons. A purely relativistic effect, the spin-orbit interaction interferes in this scale in a favorable way to be able to use the degree of freedom of the spin of the electron as a vector of transmission and reading of information. This is the central theme of this line of research, which deals specifically with the following problems: electronic and transport properties in semiconductor nanostructures; dilute magnetic semiconductor nanostructures; properties related to electron spin in semiconductor nanostructures (diffusion, relaxation and spin-polarized current). Techniques used: diagrammatic treatment for disorder, Monte Carlo simulation, many-body problems (Green function in and out of equilibrium, quantum kinetic equations, diagrammatic treatment of many bodies in transport theory).

Optical Spectroscopy of Solids

Solid Optical Spectroscopy investigates the optical properties of polycrystalline and monocrystalline samples containing impurities. The techniques used in our research are luminescence, excitation luminescence, optical absorption and photoacoustic spectroscopy, which determine the coordination of the dopant occupation site in the crystalline lattice, electronic levels, transitions and energy parameters, transition probabilities , radiative decay, quantum efficiency and network dynamics, and the optical quality of new optical systems.

In the solids in general, and in the insulating matrices in particular, the physical properties are related to punctual defects that arise in the formation of the compound, by the insertion in the host network of interstitial impurities, or by defects generated by irradiation of the samples. In the case of insulators doped with the transition metals such as chromium, iron, cobalt, nickel and manganese, the most important optical characteristic is the presence of large bands of luminescence and absorption, in the regions of visible and near infrared. The host networks are formed by closed-layer ions and, when the dopant ion is inserted, their energy levels are deployed and many of these new states depend differently on the electrostatic potential (crystalline field) generated by the ions of the first neighborhood. The transitions between two states that have different dependencies with the crystalline field originate the broad bands of emission and absorption observed in these materials, which are called vibron bands. These bands allow applications ranging from active materials to solid state laser at room temperature to use as thermoluminescent dosimeters.

Biomedical Applications Using Synchrotron Light

Images are traditionally constructed by illuminating the object of interest and recording the transmitted intensity as a function of the position in space. Usual imaging techniques are, in principle, quantitative methods for determining the spatial distribution of a physical quantity. The applications of new imaging techniques in medicine, technology and biology have gained considerable interest in the field of Medical Physics. Imaging techniques and characterization of biological tissues using spreading effects have had a pronounced impact on modern biology and are expected to be increasingly important in the future, especially to aid in the medical diagnosis of serious diseases.

During the last years several synchrotron laboratories have developed light lines dedicated to medical applications. The main feature of these sources is the broad and continuous energy spectrum that provides a high flux of photons under an energy band up to 50 keV or greater. In addition, the beam has a high natural collimation and a high degree of coherence in space and time. These features in combination with sophisticated optics make the synchrotron radiation sources suitable for medical applications as the enhancement of image quality is observed while the dose is conserved or reduced in some instances.

The National Synchrotron Light Laboratory (LNLS), located in Campinas, is the only one of its kind in the Southern Hemisphere. The LNLS, in 1987, began to carry out an ambitious project: to place Brazil in a select group of countries capable of producing synchrotron light . Since 1997, the Medical Physics group of DFAT / UERJ has participated in several projects carried out in the LNLS in the XRD1 (X-ray Diffraction), XRD2 (Magnetic Diffraction and 6 Circles) and XRF (Lightning Fluorescence) X). The projects developed are related to the characterization of healthy and cancerous human tissues by X-ray diffraction, evaluation of the elemental concentration in healthy and cancerous human tissues using X-ray fluorescence and development of the imaging technique using X-ray diffraction. been published in specialized journals and in national and international events. In addition, postgraduate and scientific initiation students are involved in fruitful collaborations with COPPE / UFRJ and with the Trieste-Elettra synchrotron laboratory.