Ph. Boucaud

Light hadrons from lattice QCD with light (u, d), strange and charm dynamical quarks

We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (Nf = 2 + 1 + 1) dynamical quarks using Wilson twisted mass fermions at maximal twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing a ≈ 0:078 fm and a ≈ 0:086 fm with lattice sizes ranging from L ≈ 1:9 fm to L ≈ 2:8 fm. We measure with high statistical precision the light pseudoscalar mass mPS and decay constant fPS in a range 270 ≲ mPS ≲ 510 MeV and determine the low energy parameters f0 and

Dynamical twisted mass fermions with light quarks

{\bar{l}_{3,4}}

Intraband absorption in n-doped InAs/GaAs quantum dots

of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to Nf = 2 results are performed.

Long-wavelength (≈15.5 μm) unipolar semiconductor laser in GaAs quantum wells

We present results of dynamical simulations with 2 flavours of degenerate Wilson twisted mass quarks at maximal twist in the range of pseudo scalar masses from 300 to 550 MeV. The simulations are performed at one value of the lattice spacing a \lesssim 0.1 fm. In order to have O(a) improvement and aiming at small residual cutoff effects, the theory is tuned to maximal twist by requiring the vanishing of the untwisted quark mass. Precise results for the pseudo scalar decay constant and the pseudo scalar mass are confronted with chiral perturbation theory predictions and the low energy constants F, \bar{l}_3 and \bar{l}_4 are evaluated with small statistical errors.

The Infrared Behaviour of the Pure Yang–Mills Green Functions

We have investigated the intraband absorption within the conduction band of InAs/GaAs quantum dots. The islands obtained by self-organized epitaxy are modulation doped with a silicon planar doping 2 nm below the dot layer plane. The dots exhibit infrared absorption polarized along the growth axis in the midinfrared spectral range. The absorption is maximum around 150 meV with a large broadening around 130 meV. This broadening is attributed to size fluctuations within the one dot layer plane and the consequent variation of the electron confinement energy with the dot size. The magnitude of the absorption along the growth axis for the one dot layer plane is ≈2.5×10−2% which corresponds to an equivalent absorption cross section σz≈3.1×10−15 cm2. We show that the intraband absorption can also be clearly observed using a photoinduced infrared absorption technique with the doped quantum dots.

On the IR behaviour of the Landau-gauge ghost propagator

A unipolar semiconductor laser emitting in the mid-infrared spectral region is demonstrated. The laser scheme relies on a simple three-level system in GaAs/AlGaAs asymmetric coupled quantum wells. Population inversion between excited states is achieved by optical pumping of electrons from the ground state with a CO2 laser. Long-wavelength (≈15.5 μm) laser emission is demonstrated. The laser is operated in the pulsed regime up to a temperature of 110 K and with an output peak power ≈0.4 W at 77 K. Unipolar quantum well semiconductor lasers based on this principle are capable of covering the long wavelength mid-infrared spectral region above 12 μm.

Detailed analysis of second‐harmonic generation near 10.6 μm in GaAs/AlGaAs asymmetric quantum wells

We review the infrared properties of the pure Yang–Mills correlators and discuss recent results concerning the two classes of low-momentum solutions for them reported in literature, i.e. decoupling and scaling solutions. We will mainly focus on the Landau gauge and pay special attention to the results inferred from the analysis of the Dyson–Schwinger equations of the theory and from “quenched” lattice QCD. The results obtained from properly interplaying both approaches are strongly emphasized.

Infrared spectroscopy of intraband transitions in self-organized InAs/GaAs quantum dots

We examine analytically the ghost propagator Dyson-Schwinger Equation (DSE) in the deep IR regime and prove that a finite ghost dressing function at vanishing momentum is an alternative solution (solution II) to the usually assumed divergent one (solution I). We furthermore find that the Slavnov-Taylor identities discriminate between these two classes of solutions and strongly support the solution II. The latter turns out to be also preferred by lattice simulations within numerical uncertainties.

Heavy → light semileptonic decays of pseudoscalar mesons from lattice QCD

We report on the observation of resonant intersubband second‐harmonic generation in asymmetric GaAs/AlGaAs quantum wells using a cw or Q‐switched tunable CO2 laser as the pumping source. The dependence of the second‐harmonic intensity with the pump photon wavelength is presented for the first time. A Lorentzian‐like second‐harmonic line shape is found with a maximum at 10.9 μm and a linewidth of 0.4 μm (4.1 meV). These results are in good agreement with theoretical predictions. The expected quadratic dependence of the second‐harmonic conversion efficiency with pump intensity is well verified for intensities up to 150 kW/cm2. The calibrated second‐harmonic power reaches 0.13 μW for a cw pump power of 0.8 W. The value of 7.2×10−7 m/V deduced for the second‐order nonlinear susceptibility is about 1900 times greater than that found in bulk GaAs.

Electroluminescence of Ge'Si self-assembled quantum dots grown by chemical vapor deposition

We have investigated the midinfrared absorption between confined levels of undoped InAs/GaAs quantum dots obtained by self-organized growth. The infrared absorption is measured by a photoinduced infrared spectroscopy. Quantum dots with different sizes are analyzed as a function of temperature, interband pump photon energy, intensity, and infrared polarization. We show that in the 90–250 meV energy range the quantum dots exhibit intraband absorption between confined levels, which are polarized along the growth axis as for usual conduction intersubband transitions in quantum wells. Intraband absorption is observed for either selective excitation of the dots or excitation via absorption in the wetting and GaAs layers. Based on the energy position and the temperature dependence, the infrared resonances are attributed to intraband transitions between confined holes and to bound-to-continuum transitions of electrons, which, respectively, shift to high and low energy as the dot size is decreased. The reported fe...