Item Accepted version Open AccessCurrent rectification in a double quantum dot through fermionic reservoir engineering(American Physical Society (APS), 2018) Malz, D; Nunnenkamp, A; Malz, Daniel [0000-0002-8832-0927]; Nunnenkamp, Andreas [0000-0003-2390-7636]Reservoir engineering is a powerful tool for the robust generation of quantum states or transport properties. Using both a weak-coupling quantum master equation and the exact solution, we show that directional transport of electrons through a double quantum dot can be achieved through an appropriately designed electronic environment. Directionality is attained through the interference of coherent and dissipative coupling. The relative phase is tuned with an external magnetic field, such that directionality can be reversed, as well as turned on and off dynamically. Our work introduces fermionic reservoir engineering, paving the way to a new class of nanoelectronic devices. Item Accepted version Open AccessAll-Optical Control of the Silicon-Vacancy Spin in Diamond at Millikelvin Temperatures.(American Physical Society, 2018-02-02) Becker, Jonas N; Pingault, Benjamin; Groß, David; Gündoğan, Mustafa; Kukharchyk, Nadezhda; Markham, Matthew; Edmonds, Andrew; Atatüre, Mete; Bushev, Pavel; Becher, ChristophThe silicon-vacancy center in diamond offers attractive opportunities in quantum photonics due to its favorable optical properties and optically addressable electronic spin. Here, we combine both to achieve all-optical coherent control of its spin states. We utilize this method to explore spin dephasing effects in an impurity-rich sample beyond the limit of phonon-induced decoherence: Employing Ramsey and Hahn-echo techniques at temperatures down to 40 mK we identify resonant coupling to a substitutional nitrogen spin bath as limiting decoherence source for the electron spin. Item Open AccessFrom the artificial atom to the Kondo-Anderson model: Orientation-dependent magnetophotoluminescence of charged excitons in InAs quantum dots(American Physical Society (APS), 2013) Van Hattem, B; Corfdir, P; Brereton, P; Pearce, P; Graham, AM; Stanley, MJ; Hugues, M; Hopkinson, M; Phillips, RT; Pearce, Phoebe [0000-0001-9082-9506]; Phillips, Richard [0000-0002-8279-3475]We present a magnetophotoluminescence study on neutral and charged excitons confined to InAs/GaAs quantum dots. Our investigation relies on a confocal microscope that allows arbitrary tuning of the angle between the applied magnetic field and the sample growth axis. First, from experiments on neutral excitons and trions, we extract the in-plane and on-axis components of the Landé tensor for electrons and holes in the s shell. Then, based on the doubly negatively charged exciton magnetophotoluminescence, we show that the p-electron wave function spreads significantly into the GaAs barriers. We also demonstrate that the p-electron g factor depends on the presence of a hole in the s shell. The magnetic field dependence of triply negatively charged excitons photoluminescence exhibits several anticrossings, as a result of coupling between the quantum dot electronic states and the wetting layer. Finally, we discuss how the system evolves from a Kondo-Anderson exciton description to the artificial atom model when the orientation of the magnetic field goes from Faraday to Voigt geometry. Item Open AccessTemperature-dependence of exciton radiative recombination in (Al,Ga)N/GaN quantum wells grown on a-plane GaN substrates(The Japan Society of Applied Physics, 2013-05) Corfdir, P; Dussaigney, A; Teisseyre, H; Suski, T; Grzegory, I; Lefebvre, P; Giraud, E; Shahmohammadi, M; Phillips, RT; Ganiere, JD; Grandjean, N; Deveaud, B; Phillips, Richard [0000-0002-8279-3475]This article presents the dynamics of excitons in a-plane (Al,Ga)N/GaN single quantum wells of various thicknesses grown on bulk GaN substrates. For all quantum well samples, recombination is observed to be predominantly radiative in the low-temperature range. At higher temperatures, the escape of charge carriers from the quantum well to the (Al,Ga)N barriers is accompanied by a reduction in internal quantum efficiency. Based on the temperature-dependence of time-resolved photoluminescence experiments, we also show how the local disorder affects the exciton radiative lifetime at low temperature and the exciton non-radiative lifetime at high temperature. Item Open AccessExciton localization mechanisms in wurtzite/zinc-blende GaAs nanowires(American Physical Society (APS), 2013) Graham, AM; Corfdir, P; Heiss, M; Conesa-Boj, S; Uccelli, E; Fontcuberta I Morral, A; Phillips, RT; Phillips, Richard [0000-0002-8279-3475]We investigate the emission properties of excitons in GaAs nanowires containing quantum disks formed by structural alternation between the zinc-blende and wurtzite phases, by means of temperature-dependent photoluminescence. At 10 K the emission from an ensemble of disks is distributed in a band of full width at half maximum ∼30 meV, whereas the emission linewidth for a single disk is 700 μeV. While the disk ensemble emission exhibits an S-shaped temperature dependence, the emission from single quantum disks follows the temperature dependence of the band gap over the whole temperature range. This indicates that intradisk exciton localization on impurities is negligible and that increasing the temperature induces a transfer of excitons from narrow to thick disks along the length of the wires. Our observations of the emission linewidth for single crystal-phase quantum disks show a scattering rate of excitons with acoustic phonons eight times larger than the values usually reported for (Al,Ga)As/GaAs quantum wells. This large scattering rate demonstrates that the electron effective mass in wurtzite GaAs is much heavier than in zinc-blende GaAs and is evidence of coupling between the Γ7 and Γ8 conduction bands of wurtzite GaAs. Item Open AccessRole of the dielectric mismatch on the properties of donors in semiconductor nanostructures bounded by air(American Institute of Physics, 2012) Corfdir, Pierre; Lefebvre, PierreWe compute by envelope function calculations the binding energy EB of donor atoms in thin slabs of semiconductor bounded by air, accounting for the dielectric mismatch between air and the semiconductor. We detail how EB depends on the donor-site and on the thickness of the slab. We show that due to the competition between surface and dielectric mismatch effects, EB does not monotonically decrease from the center to the surface of the nanostructures. Finally, we discuss our results in regard to recent photoluminescence experiments performed on ensemble and single GaN nanowires. Item Open AccessImportance of excitonic effects and the question of internal electric fields in stacking faults and crystal phase quantum discs: The model-case of GaN(American Institute of Physics, 2012) Corfdir, Pierre; Lefebvre, PierreWe compute using envelope function calculations the energy and the oscillator strength of excitons in zinc blende/wurtzite quantum wells (QWs), such as those that appear in many examples of semiconductor nanowires, and in basal plane stacking faults (BSFs). We address specifically the model-case of GaN. In addition to the electron-hole Coulomb interaction, we account for the quantum-confined Stark effect. We demonstrate that despite the type-II band alignment at the zinc blende/wurtzite interfaces, a significant binding and a rather strong oscillator strength are preserved by excitonic effects. When adjacent crystal phase QWs are coupled together, we compute increased as well as decreased exciton oscillator strength with respect to the single QW case, depending on the QW-QW coupling scheme. Comparing the results of our calculations with available data, we finally conclude in favor of the absence of built-in electric fields perpendicular to the BSF planes. Item Open AccessImpact of biexcitons on the relaxation mechanisms of polaritons in III-nitride based multiple quantum well microcavities(American Physical Society, 2012) Corfdir, Pierre; Levrat, Jacques; Rossbach, Georg; Butté, Raphaël; Feltin, Eric; Carlin, Jean-François; Christmann, Gabriel; Lefebvre, Pierre; Ganière, Jean-Daniel; Grandjean, Nicolas; Deveaud-Plédran, BenoîtWe report on the direct observation of biexcitons in a III nitride based multiple quantum well microcavity operating in the strong light-matter coupling regime by means of nonresonant continuous wave and time-resolved photoluminescence at low temperature. First, the biexciton dynamics is investigated for the bare active medium (multiple quantum wells alone) evidencing localization on potential fluctuations due to alloy disorder and thermalization between both localized and free excitonic and biexcitonic populations. Then, the role of biexcitons is considered for the full microcavity: in particular, we observe that for specific detunings the bottom of the lower polariton branch is directly fed by the radiative dissociation of either cavity biexcitons or excitons mediated by one LO-phonon. Accordingly, minimum polariton lasing thresholds are observed, when the bottom of the lower polariton branch corresponds in energy to the exciton or cavity biexciton first LO-phonon replica. This singular observation highlights the role of excitonic molecules in the polariton condensate formation process as being a more efficient relaxation channel when compared to the usually assumed acoustical phonon emission one.