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  • Resultat 1-10 av 76
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1.
  • Kristinsdottir, Liney Halla, et al. (författare)
  • Total current blockade in an ultracold dipolar quantum wire.
  • 2013
  • Ingår i: Physical Review Letters. - 1079-7114. ; 110:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Cold-atom systems offer a great potential for the future design of new mesoscopic quantum systems with properties that are fundamentally different from semiconductor nanostructures. Here, we investigate the quantum-gas analogue of a quantum wire and find a new scenario for the quantum transport: Attractive interactions may lead to a complete suppression of current in the low-bias range, a total current blockade. We demonstrate this effect for the example of ultracold quantum gases with dipolar interactions.
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3.
  • Ayedh, Hussein, et al. (författare)
  • Acoustic phonons in nanowires with embedded heterostructures
  • 2011
  • Ingår i: Journal of Nanomaterials. - : Hindawi Limited. - 1687-4129 .- 1687-4110. ; 2011
  • Tidskriftsartikel (refereegranskat)abstract
    • Abstract in Undetermined Acoustic phonons are studied in finite nanowires based on the elastic continuum model. The phonon dispersion relations are compared for different types of approximations both for pure nanowires and nanowire heterostructures including cubic and wurtzite materials. We find that the isotropic approximation highly underestimates the frequency of torsional modes. The impact of heterostructures on the lowest modes is rather weak and can be described by an average of the different structure parameters.
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4.
  • Banit, F, et al. (författare)
  • Self-consistent theory of the gain linewidth for quantum-cascade lasers
  • 2005
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:4, s. 1-41108
  • Tidskriftsartikel (refereegranskat)abstract
    • The linewidth in intersubband transitions can be significantly reduced below the sum of the lifetime broadening for the involved states, if the scattering environment is similar for both states. This is studied within a nonequilibrium Green function approach here. We find that the effect is of particular relevance for a recent, relatively low doped, Terahertz quantum-cascade laser.
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5.
  • Carosella, F., et al. (författare)
  • Free-carrier absorption in quantum cascade structures
  • 2012
  • Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 85:8
  • Tidskriftsartikel (refereegranskat)abstract
    • We show that the free-carrier absorption in quantum cascade lasers (QCLs) is very small and radically different from the classical Drude result due to the orthogonality between the direction of the carrier free motion and the electric field of the laser emission. A quantum mechanical calculation of the free-carrier absorption and intersubband oblique absorption induced by interface defects, Coulombic impurities, and optical phonon absorption/emission is presented for QCLs with a double-quantum-well design. The interaction between the electrons and the optical phonons dominates at room temperature.
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6.
  • Carosella, F., et al. (författare)
  • One-dimensional massless Dirac bands in semiconductor superlattices
  • 2014
  • Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 89:23
  • Tidskriftsartikel (refereegranskat)abstract
    • Semiconductor superlattices may display dispersions that are degenerate either at the zone center or zone boundary [G. Bastard, Wave Mechanics Applied to Semiconductor Heterostructures, Monographies de Physique (Les Editions de Physique, Les Ulis, 1988); C. Sirtori, F. Capasso, D. L. Sivco, and A. Y. Cho, Appl. Phys. Lett. 64, 2982 (1994)]. We show that they are linear upon the wave vector in the vicinity of the crossing point. This establishes a realisation of massless Dirac bands within semiconductor materials. We show that the eigenstates and the corresponding Wannier functions of these superlattices have peculiar symmetry properties. We discuss the stability of the properties of such superlattices versus the electron in-plane motion. As a distinct fingerprint, the inter-sub-band magnetoabsorption spectrum for such superlattices is discussed.
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7.
  • Dorsch, Sven, et al. (författare)
  • Heat Driven Transport in Serial Double Quantum Dot Devices
  • 2021
  • Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 21:2, s. 988-994
  • Tidskriftsartikel (refereegranskat)abstract
    • Studies of thermally induced transport in nanostructures provide access to an exciting regime where fluctuations are relevant, enabling the investigation of fundamental thermodynamic concepts and the realization of thermal energy harvesters. We study a serial double quantum dot formed in an InAs/InP nanowire coupled to two electron reservoirs. By means of a specially designed local metallic joule-heater, the temperature of the phonon bath in the vicinity of the double quantum dot can be enhanced. This results in phonon-assisted transport, enabling the conversion of local heat into electrical power in a nanosized heat engine. Simultaneously, the electron temperatures of the reservoirs are affected, resulting in conventional thermoelectric transport. By detailed modeling and experimentally tuning the interdot coupling, we disentangle both effects. Furthermore, we show that phonon-assisted transport is sensitive to excited states. Our findings demonstrate the versatility of our design to study fluctuations and fundamental nanothermodynamics.
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8.
  • Dupont, E., et al. (författare)
  • A phonon scattering assisted injection and extraction based terahertz quantum cascade laser
  • 2012
  • Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 111:7
  • Tidskriftsartikel (refereegranskat)abstract
    • A lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the GaAs/Al0.25Ga0.75As material system that maximizes the product of population inversion and oscillator strength at 150 K. The fabricated devices using Au double-metal waveguides show lasing at 3.2 THz up to 138 K. The electrical characteristics display no sign of differential resistance drop at lasing threshold, which, in conjunction with the low optical power of the device, suggest-thanks to the rate equation model-a slow depopulation rate of the lower lasing state, a hypothesis confirmed by non-equilibrium Green's function calculations. [http://dx.doi.org/10.1063/1.3702571]
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9.
  • Franckie, Martin, et al. (författare)
  • Comparative analysis of quantum cascade laser modeling based on density matrices and non-equilibrium Green's functions
  • 2014
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:10
  • Tidskriftsartikel (refereegranskat)abstract
    • We study the operation of an 8.5 mu m quantum cascade laser based on GaInAs/AlInAs lattice matched to InP using three different simulation models based on density matrix (DM) and non-equilibrium Green's function (NEGF) formulations. The latter advanced scheme serves as a validation for the simpler DM schemes and, at the same time, provides additional insight, such as the temperatures of the sub-band carrier distributions. We find that for the particular quantum cascade laser studied here, the behavior is well described by simple quantum mechanical estimates based on Fermi's golden rule. As a consequence, the DM model, which includes second order currents, agrees well with the NEGF results. Both these simulations are in accordance with previously reported data and a second regrown device. (C) 2014 AIP Publishing LLC.
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10.
  • Franckie, Martin, et al. (författare)
  • Injection schemes in THz quantum cascade lasers under operation
  • 2013
  • Ingår i: Proceedings of SPIE. - : SPIE. - 9780819496966 ; 8846
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The two main design schemes for Terahertz quantum cascade lasers, based on tunnelling and scattering injection, respectively, are theoretically compared. We apply our simulation package based on the non-equilibrium Green’s function technique. Our results provide a good description of the gain degradation with temperature. Thermal backfilling contributes to decrease of population inversion in both cases. However, the dropping inversion cannot account for the total reduction of gain.
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  • Resultat 1-10 av 76

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