D. Giratá

In-plane electrodynamics of the superconductivity inBi2Sr2CaCu2O8+δ: Energy scales and spectral weight distribution

The in-plane infrared and visible (3 meV–3 eV) reflectivity of Bi2Sr2CaCu2O8+� (Bi-2212) thin films is measured between 300 K and 10 K for different doping levels with unprecedented accuracy. The optical conductivity is derived through an accurate fitting procedure. We study the transfer of spectral weight from finite energy into the superfluid as the system becomes superconducting. In the over-doped regime, the superfluid develops at the expense of states lying below 60 meV, a conventional energy of the order of a few times the superconducting gap. In the underdoped regime, spectral weight is removed from up to 2 eV, far beyond any conventional scale. The intraband spectral weight change between the normal and superconducting state, if analyzed in terms of a change of kinetic energy is � 1 meV. Compared to the condensation energy, this figure addresses the issue of a kinetic energy driven mechanism.

Structural and Electrical Properties of Grain Boundary Josephson Junctions Based on Bi2Sr2CaCu2O8+δ Thin Films

An in situ deposition sputtering process at high pressure has been developed for preparing high quality superconducting Bi2Sr2CaCu2O8+δ thin films on different substrates. Both microstructural and electrical properties were well characterized by TEM, AFM, RBS, X-ray diffraction, resistivity and magnetic susceptibility. The high reproducibility of the film quality facilitated a detailed study of Josephson effect in bicrystalline grain boundary junctions (GBJs). Thin films were deposited on (001) SrTiO3 bicrystals with misorientation angles of 24° and patterned by a photolithography process using Br-ethanol chemical etching. The width of the microbridges ranges from 10 to 50 μm. The critical current densities across the grain boundary have been measured and compared to the critical current in the film. A modulation in the critical current was found under magnetic field and also Shapiro steps in the I–V curves under microwave irradiation have been observed indicating a Josephson behavior. Electrical properties are well described by the resistively shunted junction (RSJ) model. The IcRn product reaches values around 2.0 mV at 4.2 K.

Characterization of La2/3Ca1/3xMnO3 with Low Doping of Fe and Cr (abstract)

We have characterized magnetization, transport, and structure of La2/3Ca1/3MnO3 thin films and bulk powder samples undoped and with low doping of 57Fe (1% and 3%) and Cr (6%, 7%, and 8%). The powder samples were synthesized by solid‐state reaction and thin films grown on (100)‐SrTiO3 STO, and (100)‐LaAlO3 LAO single‐crystal substrates by high O2 pressure (500 mTorr) using dc magnetron sputtering. We found changes in the values of the magnetoresistance and metal‐insulator transition temperatures, as well as the magnetization and Curie temperatures. These behaviors are dependent of the composition of the samples. However, we observed from the hysteresis loops that the coercitive field did not change significantly with Cr or Fe addition at different temperatures. Doping decreased the double exchange and the ferromagnetic order, possibly due to the competing influences from the strain relaxation.

Women in Physics and Scientific Research in Colombia

Generally speaking, scientists in Colombia do not have a role in changing the social or economic situation of the nation. Although the proportion of women who study physics increases slowly year by year, the number of women who work in physics research has not considerably increased. Many problems in Colombia might be solved if women’s status as researchers in Colombia changed. It is necessary to promote a national project for improving women’s status in the sciences and to present this project to the Colombian government. Many Colombian women have grown up believing they are not able to take scientific jobs, and therefore choose to study other disciplines “for women.” If Colombian women found opportunities in physics and the sciences in general, they would likely pursue such disciplines, but we need government support to promote an efficient program that will give women more information about physics as a feasible career option.

SURFACE TOPOGRAPHY ON EPITAXIAL HoBa2Cu3O7-δ AND Bi2Sr2CaCu2O8+δ THIN FILMS

Surface topography on epitaxial HoBa2Cu3O7-δ (HBCO) and Bi2Sr2CaCu2O8+δ (BSCCO) thin films analysis by using the atomic force microscopy (AFM) technique was carried out. The films were deposited in situ on SrTiO3 substrates with thicknesses ranging from 100 to 300 nm by a high-pressure sputtering process. Chemical etching with a nonaqueous solution of Br-ethanol was used to modify the surface of the samples. HBCO films showed spiral grains, while BSCCO samples exhibited a terraced growth. Etching with Br-ethanol has different effects on HBCO and BSCCO. In HBCO, etching produces clean surfaces with light changes on the surface morphology, whereas in BSCCO it conduces to strong changes in the structure and the roughness of the film surface.