J. Rubio

Phonon Raman scattering in quantum wires

Abstract Phonons in narrow quantum wires of In 0.53 Ga 0.47 As showing strong one-dimensional confinement of carriers have been studied by Raman spectroscopy. A strong enhancement of the Raman intensity of the longitudinal optical phonon of the wires is observed for wire widths decreasing down to 40 nm. For narrower wires (10–30 nm), the Raman intensity falls very rapidly as the surface roughness becomes comparable to the wire width. No changes in the phonon frequency have been observed. The increased Raman intensity is attributed to enhanced resonance effects due to the one-dimensional confinement of carriers. The role of wavevector non-conservation and surface electric fields on the Frohlich scattering efficiency are discussed.

Site selective spectroscopy under high magnetic field in KGd(WO4)2 :Nd crystals

Abstract The emission and excitation spectra of Nd3+ ions in KGd(WO4)2 crystals have been studied showing a clear structure in the single transitions associated with Stark sublevels of Nd3+ ions at low temperature. In this work, site selective spectroscopy under the presence of high magnetic field (up to 10 T) has been used. A variety of Nd3+ centers is responsible for the shape of the spectra at 0 T, which can not be selectively excited. By increasing magnetic field Zeeman splitting of the Stark levels is observed and the Nd3+ centers can be selectively excited. The Zeeman splitting is in agreement with an effective giromagnetic factor of 2.01 for the lowest Kramer doublet of the 4I11/2 state of Nd3+ ions.

Magnetic field dependence of many-body processes in quantum well luminescence

The effect of electron-electron interactions on the optical properties of a two-dimensional electron gas under magnetic fields is studied in a modulation-doped single quantum well of InGaAs. Optical singularities at the Fermi level and shake-up side-bands are observed at low temperatures. Their intensities and lineshapes undergo drastic changes which are periodic in the filling factor. The results are interpreted in terms of the magnetic-field dependent screening properties of the two-dimensional electron gas.

Many-body effects in photoluminescence of a two-dimensional electron gas in high magnetic field

Abstract The behaviour of a two-dimensional electron gas has been studied in a series of modulation doped quantum wells of the type In 0.53 Ga 0.47 As/InP with different electron densities. The low energy sidebands in the optical emission spectra in high magnetic field due to many-body effects have been investigated. In a sample with a high electron density the first shake-up sideband is followed up to 20 T, where it reappears after crossing with phonon replicas. Its intensity profile in high magnetic field confirms previous interpretations on the filling factor dependence. In a sample with a lower electron density, polarization measurements illustrated the emptying of the higher spin state in the first Landau level, reaching a high degree of polarization at a filling factor below one.

Role of the valence-band mass on the many-body optical properties of a two-dimensional electron gas

Abstract The Fermi-edge singularity and shake-up sidebands have been measured in the optical emission spectrum of a modulation doped single quantum well of InGaAs/InP with spatially variable Fermi energy and valence-band mass. Both magnitudes change across the sample due to a slight variation of the well width. The intensity of the optical Fermi-edge singularity at zero magnetic field increases with increasing hole mass, in excellent quantitative agreement with our many-body calculations. Emission spectra under a magnetic field at even filling factors show that, contrary to the Fermi-edge singularity, shake-up bands do not depend on the hole mass, in qualitative agreement with previous calculations.