A5068919650- Semiconductor Quantum Structures and Devices
- Quantum and electron transport phenomena
- Physics of Superconductivity and Magnetism
- Graphene research and applications
- Semiconductor materials and devices
- Advancements in Semiconductor Devices and Circuit Design
- Magnetic properties of thin films
- Electronic and Structural Properties of Oxides
- Diamond and Carbon-based Materials Research
- Semiconductor Lasers and Optical Devices
- Quantum optics and atomic interactions
- GaN-based semiconductor devices and materials
- Quantum, superfluid, helium dynamics
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum Dots Synthesis And Properties
- Photonic and Optical Devices
- Topological Materials and Phenomena
- Graphene and Nanomaterials Applications
- 2D Materials and Applications
- Characterization and Applications of Magnetic Nanoparticles
- Spectroscopy and Laser Applications
- Laser Design and Applications
- Carbon Nanotubes in Composites
- Near-Field Optical Microscopy
- Magneto-Optical Properties and Applications
University of Exeter
2004-2021
National Research Council
2011
The University of Texas at Austin
2010
University of Nottingham
2010
AT&T (United States)
1996
Dartmouth College
1996
Max Planck Institute for Solid State Research
1990-1992
Laboratoire National des Champs Magnétiques Intenses
1990-1991
Centre National de la Recherche Scientifique
1990-1991
Max Planck Society
1990-1991
The magnitude and sign of the effective magnetic splitting factor ${\mathit{g}}^{\mathrm{*}}$ for conduction electrons in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wells have been determined as a function well width down to 5 nm. experimental method is based on combined measurements decay time photoluminescence suppression its circular polarization under polarized optical pumping field perpendicular growth axis (Hanle effect)....
Below a critical filling factor (${\ensuremath{\nu}}_{\mathit{c}}$=0.28) and temperature (${\mathit{T}}_{\mathit{c}}$=1.4 K at 26 T) an additional line has been observed in the luminescence spectrum of GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterojunction; it grows intensity with decreasing \ensuremath{\nu}, dominating \ensuremath{\nu}1/11. Its appearance is accompanied by strong reduction overall integrated intensity, while its relative...
Discontinuities have been observed in the energy dependence on magnetic field of luminescence line corresponding to 2D electron-hole recombination GaAs/AlGaAs heterojunctions at filling factors \ensuremath{\nu}=2/3, 1/3, 4/5, 3/5, 2/5, 1/5, 1/7, and 1/9. We associate these energy-position shifts with discontinuous behavior chemical potential due condensation electrons into an incompressible Fermi-liquid state, thereby evaluate gaps fractional down
Remarkable softenings of long wavelength intersubband spin excitations dilute electron double layers are observed at even integer quantum Hall states. These in coupled GaAs wells were probed by resonant inelastic light scattering. Their softening is attributed to enhanced exchange vertex corrections (excitonic binding) the The collapse spin-density mode with $\ensuremath{\delta}{S}_{z}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ an energy close Zeeman splitting suggests existence...
The energy spectra of isolated one-dimensional (1D) electron channels have been studied by photoluminescence in zero and finite magnetic fields B. Arrays periodic quantum wires (period =290--400 nm, width =150--170 nm) were etched from modulation-doped ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/GaAs heterojunctions, with special low-concentration Be \ensuremath{\delta} doping the buffer layer to increase intensity. We able attain 1D limit, i.e.,...
Inelastic light scattering by low-energy spin-excitations reveals three distinct configurations of spin electron double layers in gallium arsenide quantum wells at even-integer Hall states. The transformations among these states appear as phase transitions driven the interplay between Coulomb interactions and Zeeman splittings. One correlates with emergence a spin-flip intersubband excitation vanishingly low energy provides direct evidence link soft collective excitations two-dimensional system.
While thermally cycling monolayer, bilayer, and trilayer graphene between 5 K 300 K, Raman spectroscopy has shown that cooling to induces a strain in these flakes of −0.081 ± 0.003%. This was used measure the thermal expansion coefficient (TEC), which found be (−3.2 0.2)×10−6 K−1 for monolayers, (−3.4 0.4)×10−6 bilayers, (−3.8 0.6)×10−6 trilayers at room temperature. The TEC showed similar temperature dependence across all thicknesses good agreement with theoretical predictions. study, thus,...
Interband reflectivity measurements have been performed on a variety of GaAs-${\mathrm{Ga}}_{0.64}$${\mathrm{Al}}_{0.36}$As multiple-quantum-well structures, in magnetic fields up to 9.5 T, applied perpendicular the layers. Sharp features are observed spectra at 1.8 K, which identified as excitonic Landau-level transitions between hole subbands and electron wells. The relative positions resonances obtained from comparison calculated structures with experimental data. seen data persist down...
We report measurements of optically induced density depletion the two-dimensional electron system formed at interface a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterojunction with \ensuremath{\delta}-doped layer Be acceptors in GaAs 250 \AA{} from interface. Our show that low laser power effect is controlled by recombination electrons photoexcited holes have become bound to acceptors. The point which all sample been neutralized indicated sudden...
We have investigated the radiative recombination of two-dimensional (2D) electrons with holes bound to acceptors from a \ensuremath{\delta} layer, positioned at well-defined distance interface, in n-type GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As single heterojunctions and thereby characterized system by photoluminescence photoluminescence-excitation techniques. Using magnetotransport magneto-optics we demonstrate that, under continuous...
We have studied photoluminescence from GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As strain-induced quantum dots in a magnetic field. These high radiative efficiency and long (\ensuremath{\sim}ns) luminescent decay times. At low excitation intensities, corresponding to average carrier densities of less than one electron-hole pair per dot, excited-state (``hot'') luminescence due slow interstate relaxation is observed. intermediate where there are...
Low-energy spin-density intersubband excitations of electron bilayers in GaAs double quantum wells have been investigated by inelastic light scattering the search for unstable modes. Excitonic vertex corrections due to exchange Coulomb interactions were thus determined down very low densities. The experiments are interpreted within time-dependent local-density approximation (TDLDA) and with a nonlocal theory. pronounced softening at zero magnetic field (a vertex-correction driven...
Coherent ultrathin GaAsN insertions are formed in a GaN matrix by predeposition of an GaAs layer on surface, followed annealing NH3 atmosphere and overgrowth with GaN. During the overgrowth, most As atoms substituted N, dense array coherent nanodomains lateral sizes about 3-4 nm matrix. We report green luminescence due to insertions, surviving at high observation temperatures excitation densities.
We have obtained a two-dimensional electron-solid phase diagram in the extreme magnetic quantum limit by studying temperature dependence of radiative recombination electrons GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterojunction with holes bound to \ensuremath{\delta} layer, 250 \AA{} away GaAs, Be acceptors. The low-energy shoulder luminescence line, indicating presence electron solid, is seen disappear at filling-factor-dependent critical...
We have performed magnetophotoluminescence and magnetophotoluminescence-excitation spectroscopy at 1.8 K on a GaAs/${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{Al}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum-well structure in which the carrier density single 50 \AA{} quantum well can be varied from zero up to about 2\ifmmode\times\else\texttimes\fi{}${10}^{11}$ carriers ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ by use of Schottky gate. This results transfer either electrons or holes...
We have measured the optical saturation intensity of GaAs quantum dots and found it to be 50 W/cm2; more than an order magnitude smaller that reported for wells. Compared such wells, our also show a larger amount saturation, again by magnitude. find depends exponentially on photoexcitation energy, with greater intensities required photon energies closer bottom dot confinement potential.
We have measured the circular photogalvanic effect in a GaAs two-dimensional hole gas zero and perpendicular magnetic field. The increase of photoinduced voltage very small field, when excited at fixed photon energy, demonstrates behavior reminiscent that seen anomalous Hall measurements on ferromagnets. spectral dependence field exhibits series maxima minima oscillate around volts. When plotted, energy positions these peaks form clear Landau-level-like fan chart.