Showing papers by "Simon Brown published in 1996"
TL;DR: The influence of the doubly occupied bound state (${X}^{\ensuremath{-}}$) on the line shape is discussed and the results with realistic many-body calculations are compared.
Abstract: We have obtained absolute interband absorption spectra from a series of modulation-doped GaAs/${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As multiple quantum wells covering a wide range of two-dimensional electron densities. The evolution of the threshold line shape from an exciton to a Fermi-edge singularity is quantified. We discuss the influence of the doubly occupied bound state (${X}^{\ensuremath{-}}$) on the line shape and compare the results with realistic many-body calculations.
34 citations
TL;DR: A low-temperature magnetotransport study of two double GaAs quantum well, triple AlAs barrier resonant tunneling structures demonstrates the critical influence of the second quantum well on the tunneling behavior, and identifies tunneling transitions that are unique to triple-barrier structures.
Abstract: We present a low-temperature (mK) magnetotransport study, using intense pulsed magnetic fields to 50 T, of two double GaAs quantum well, triple AlAs barrier resonant tunneling structures, which demonstrates the critical influence of the second quantum well on the tunneling behavior. We show that charge accumulation in the first well, and thus the overall tunneling characteristic, is controlled by the position of the lowest bound state in the second well, and identify tunneling transitions that are unique to triple-barrier structures. We also demonstrate that the tunneling current is sensitive to integer and fractional quantum Hall effect states, and find that the voltage-tunable accumulation of charge in one of the samples provides an unusual environment for the study of ground states of a two-dimensional electron system. \textcopyright{} 1996 The American Physical Society.
22 citations
TL;DR: In this article, the authors present a ballistic weak localization process in which the contributing classical trajectories pass directly between the entrance and exit leads and are not shaped by the walls of the cavity but purely by the profiles of the leads.
Abstract: Weak localization, a semiclassical process established in disordered systems, has recently been used as an experimental probe of the classical dynamics of ballistic cavities. Through a systematic study of the classical and quantum behaviour of three ballistic cavities featuring large width to length aspect ratios, we highlight the important role of the entrance and exit leads. We present a novel ballistic weak localization process in which the contributing classical trajectories pass directly between the entrance and exit leads and are not shaped by the walls of the cavity but purely by the profiles of the leads. This demonstration of a small section of a cavity supporting a `local' weak localization process has important implications for studies which relate cavity geometry to the dynamics it supports.
2 citations
TL;DR: In this article, theoretical and experimental results on the evolution of the threshold absorption of a 2D electron gas as a function of electron density were presented, focusing on the low density regime where the spectrum evolves from an exciton to a Fermi edge singularity.
1 citations
05 Jul 1996
TL;DR: In this paper, the phase diagram of the upper critical field versus temperature has been investigated for various layer thicknesses with the field both parallel and perpendicular to the layers, and the results are shown to conform with existing theories on layered superconductors.
Abstract: We report results of measurements on the superconductor/insulator system consisting of alternating layers of amorphous Ta and amorphous Ge. This system is relatively complex owing to a very thin mixed interface layer in which the pairing interaction is stronger than in the Ta itself. Measurements have now been performed using a dilution refrigerator at temperatures down to 50 mK, and using magnetic fields of up to 14 tesla. The phase diagram of the upper critical field versus temperature has been investigated for various layer thicknesses with the field both parallel and perpendicular to the layers. The results are shown to conform with existing theories on layered superconductors. The nonlinear I-V characteristic of these multilayers is also analyzed in zero field for a sample with thin superconducting layers and evidence for a Kosterlitz- Thouless transition is observed.