Optical properties of potential-inserted quantum wells in the near infrared and Terahertz ranges

We propose an engineering of the optical properties of GaAs/AlGaAs quantum wells using AlAs and InAs monolayer insertions. A quantitative study of the effects of the monolayer position and the well thickness on the interband and intersubband transitions, based on the extended-basis sp3d5s* tight-binding model, is presented. The effect of insertion on the interband transitions is compared with existing experimental data. As for intersubband transitions, we show that in a GaAs/AlGaAs quantum well including two AlAs and one InAs insertions, a three level {e1 , e2 , e3 } system where the transition energy e3-e2 is lower and the transition energy e2-e1 larger than the longitudinal optical phonon energy (36 meV) can be engineered together with a e3-e2 transition energy widely tunable through the TeraHertz range

A neotype designation for the Ascension Frigatebird Fregata aquila (Aves: Fregatidae)

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Nondissipative Addressing for Time-Division SQUID Multiplexing

International audienceRecent and future astronomical instruments are based on a focal plane mapped by a large array of superconducting bolometers. Cryogenic analog multiplexing readout techniques, based on superconducting quantum interference devices (SQUIDs), are currently developed to achieve the readout of large arrays of this kind of low noise background-limited detectors. To effectively reduce the number of cryogenic wires (particularly, SQUID biasing), line/column addressing is currently used in time-division multiplexing, i.e., same biasing is applied to a few SQUIDs (on a line) of different columns. This technique should dramatically increase power consumption if parallel biasing is applied via resistors to isolate each column; the power budget is particularly limited on this kind of front-end cryogenic readout. A design with one transformer per SQUID is also used to read out SQUID biased in series with no excess of consumption and crosstalk. We propose here a new biasing technique using simple surface-mounted capacitors, which is easier to implement. These capacitors are used to parallel bias SQUIDs without additional Joule effect while minimizing crosstalk. However, capacitors do not allow dc biasing and need a current mean value equal to zero to avoid biasing source saturation. We have then tested square current biasing through capacitors on a commercial SQUID. This measurement shows that capacitors are able to proper bias SQUID and then to perform a nondissipative addressing for time-division SQUID multiplexing

Hot electron cooling by acoustic phonons in graphene

We have investigated the energy loss of hot electrons in metallic graphene by means of GHz noise thermometry at liquid helium temperature. We observe the electronic temperature T / V at low bias in agreement with the heat diffusion to the leads described by the Wiedemann-Franz law. We report on $T\propto\sqrt{V}$ behavior at high bias, which corresponds to a T4 dependence of the cooling power. This is the signature of a 2D acoustic phonon cooling mechanism. From a heat equation analysis of the two regimes we extract accurate values of the electron-acoustic phonon coupling constant $\Sigma$ in monolayer graphene. Our measurements point to an important effect of lattice disorder in the reduction of $\Sigma$, not yet considered by theory. Moreover, our study provides a strong and firm support to the rising field of graphene bolometric detectors.Comment: 5 figure

Ecological assessment of groundwater ecosystems disturbed by recharge systems using organic matter quality, biofilm characteristics and bacterial diversity

International audienc

Intrinsic interface states in InAs-AlSb heterostructures

We examine the possibility of intrinsic interface states bound to the plane of In-Sb chemical bonds at InAs/AlSb interfaces. Careful parameterization of the bulk materials in the frame of the extended basis spds^* tight-binding model and recent progress in predictions of band offsets severely limit the span of tight-binding parameters describing this system. We find that a heavy-hole like interface state bound to the plane of In-Sb bonds exists for a large range of values of the InSb/InAs band offset

Webs of Lagrangian Tori in Projective Symplectic Manifolds

For a Lagrangian torus A in a simply-connected projective symplectic manifold M, we prove that M has a hypersurface disjoint from a deformation of A. This implies that a Lagrangian torus in a compact hyperk\"ahler manifold is a fiber of an almost holomorphic Lagrangian fibration, giving an affirmative answer to a question of Beauville's. Our proof employs two different tools: the theory of action-angle variables for algebraically completely integrable Hamiltonian systems and Wielandt's theory of subnormal subgroups.Comment: 18 pages, minor latex problem fixe

Measurement of miniband parameters of a doped superlattice by photoluminescence in high magnetic fields

We have studied a 50/50\AA superlattice of GaAs/Al$_{0.21}$Ga$_{0.79}$As composition, modulation-doped with Si, to produce $n=1.4\times 10^{12}$ cm$^{-2}$ electrons per superlattice period. The modulation-doping was tailored to avoid the formation of Tamm states, and photoluminescence due to interband transitions from extended superlattice states was detected. By studying the effects of a quantizing magnetic field on the superlattice photoluminescence, the miniband energy width, the reduced effective mass of the electron-hole pair, and the band gap renormalization could be deduced.Comment: minor typing errors (minus sign in eq. (5)

STM images of sub-surface Mn atoms in GaAs: evidence of hybridization of surface and impurity states

We prove that scanning tunneling microscopy (STM) images of sub-surface Mn atoms in GaAs are formed by hybridization of the impurity state with intrinsic surface states. They cannot be interpreted in terms of bulk-impurity wavefunction imaging. High atomic resolution images obtained using a low-temperature apparatus are compared with advanced, parameter-free tight-binding simulations accounting for both the buckled (110) surface and vacuum electronic properties