Universality and Phase Diagram around Half-filled Landau Level

Gated GaAs/AlGaAs heterostructures were used to determine the low-temperature behavior of the two-dimensional electron gas near filling factor nu=1/2 in the disorder-magnetic-field plane. We identify a line on which sigma_{xy} is temperature independent, has value sigma_{xy}=0.5 (e^{2}/h), and a distinct line on which rho_{xy}=2 (h/e^{2}). The phase boundaries between the Hall insulator and the principal quantum Hall liquids at nu=1 and 1/3 show levitation of the delocalized states of the first Landau levels for electrons and composite fermions. Finally, the data suggest that there is no true metallic phase around nu=1/2.Comment: 7 pages (Revtex), 5 figure

Observation of the screening signature in the lateral photovoltage of electrons in the Quantum Hall regime

The lateral photovoltage generated in the plane of a two-dimensional electron system (2DES) by a focused light spot, exhibits a fine-structure in the quantum oscillations in a magnetic field near the Quantum Hall conductivity minima. A double peak structure occurs near the minima of the longitudinal conductivity oscillations. This is the characteristic signature of the interplay between screening and Landau quantization.Comment: 4 pages, 4 figures, to be published in Phys. Rev.

Tsunamigenic-seismogenic structures, neotectonics, sedimentary processes and slope instability on the southwest Portuguese Margin

Tectonically active structures prone to cause devastating earthquakes and tsunamis, e.g. the Lisbon 1755 earthquake, were investigated during the UNESCO/IOC Training Through Research-10 (TTR-10) cruise on the southwest Portuguese Continental Margin using single channel seismic profiles, a 3.5-kHz hull-mounted sea-bottom profiler, 10-kHz OKEAN long range side-scan sonar, 30-kHz ORETECH deep-towed side-scan sonar, and a high-resolution deep-towed sea-bottom profiler. These data allowed the definition of new active faults and the establishment of morphological criteria for the classification of active faults in the study area. Landslides associated with the activity of a major tectonic structure, the Marquês de Pombal Fault, and other areas with clear signs of mass wasting phenomena were mapped. A slope-to-basin sedimentary system comprising 21 sedimentary ridges up to 20 km long was mapped and described. It was found that the sediments are mainly transported into the deep basins by mass transport processes across the steepest fault scarps forming a channel–levee system, while gravitational slides/slumps dominate the shallower slopes. The sedimentary ridges with an elevation of 40–50 m (50–60 ms TWT) above the seafloor are imaged on the high-resolution seismic profiles as an alternation of high and low amplitude reflectors. It is shown that the Pereira de Sousa Fault, its plateau and the Príncipes de Avis Plateau are experiencing uplift according to sedimentary and morphological criteria.<br/