167 research outputs found
Photoluminescence rings in Corbino disk at quantizing magnetic fields
Spatially resolved photoluminescence of modulation doped AlGaAs/GaAs
heterojunction was investigated in a sample of Corbino disk geometry subject to
strong perpendicular magnetic fields. Significant spatial modulation of the
photoluminescence was observed in form of one or more concentric rings which
travelled across the sample when the magnetic field strength was varied. A
topology of the observed structure excludes the possibility of being a trace of
an external current. The effect is attributed to formation of compressible and
incompressible stripes in a 2DEG density gradient across the sample.Comment: 5 two-column pages, 4 figures (one of them in color
Can an electric current orient spins in quantum wells?
A longstanding theoretical prediction is the orientation of spins by an
electrical current flowing through low-dimensional carrier systems of
sufficiently low crystallographic symmetry. Here we show by means of terahertz
transmission experiments through two-dimensional hole systems a growing spin
orientation with an increasing current at room temperature.Comment: 5 pages, 2 figure
Circular photogalvanic effect induced by monopolar spin orientation in p-GaAs/AlGaAs MQW
The circular photogalvanic effect (CPGE) has been observed in (100)-oriented
-GaAs/AlGaAs quantum wells at normal incidence of far-infrared radiation. It
is shown that monopolar optical spin orientation of free carriers causes an
electric current which reverses its direction upon changing from left to right
circularly polarized radiation. CPGE at normal incidence and the occurence of
the linear photogalvanic effect indicate a reduced point symmetry of studied
multi-layered heterostructures. As proposed, CPGE can be utilized to
investigate separately spin polarization of electrons and holes and the
symmetry of quantum wells.Comment: 4 pages, 3 figure
Spin-sensitive Bleaching and Spin-Relaxation in QW's
Spin-sensitive saturation of absorption of infrared radiation has been
investigated in p-type GaAs QWs. It is shown that the absorption saturation of
circularly polarized radiation is mostly controlled by the spin relaxation time
of the holes. The saturation behavior has been investigated for different QW
widths and in dependence on the temperature with the result that the saturation
intensity substantially decreases with narrowing of QWs. Spin relaxation times
were experimentally obtained by making use of calculated (linear) absorption
coefficients for inter-subband transitions
Nonlinear subgap photoconductivity of polycrystalline silicon
The photoconductance of polycrystalline silicon films at photon energies smaller than the band gap has been measured as a function of intensity applying a 1.3 ÎŒm wavelength semiconductor laser. The observed photosignal increases superlinearly at low intensities and saturates above about 1.5 W/cmâ2. This distinct nonlinearity is caused by a significant energy dependence of optical to thermal cross sections of trap states in the band gap. Assuming a threeâlevelârate equation model, grain boundary trap densities were evaluated
Near-field induced FIR Josephson-detection by x-axis-oriented YBa_{2}Cu_{3}O_{7-d} -films
A novel approach to intrinsic Josephson-detection of far infrared radiation is reported utilizing near-zone field effects at electric contacts on c-axis oriented YBa2Cu3O7- films. While only a bolometric signal was observed focusing the radiation far off the contacts on c-axis normal films, irradiating the edge of contacts yielded an almost wavelength independent fast signal showing the characteristic intensity dependence of Josephson-detection. The signal is attributed to a c-axis parallel component of the electric radiation field being generated in the near-zone field of diffraction at the metallic contact structures
- âŠ