Measurement of the CP-violating phase ϕ(s) in the decay B(s)(0) → J/ψϕ

We present a measurement of the time-dependent CP-violating asymmetry in B(s)(0) → J/ψ? decays, using data collected with the LHCb detector at the LHC. The decay time distribution of B(s)(0) → J/ψ? is characterized by the decay widths Γ(H) and Γ(L) of the heavy and light mass eigenstates, respectively, of the B(s)(0) - B(s)(0) system and by a CP-violating phase ?(s). In a sample of about 8500 B(s)(0) → J/ψ? events isolated from 0.37 fb(-1) of pp collisions at sqrt[s] = 7 TeV, we measure ?(s) = 0.15 ± 0.18(stat) ± 0.06(syst) rad. We also find an average B(s)(0) decay width Γ(s) ≡ (Γ(L) + Γ(H))/2 = 0.657 ± 0.009(stat) ± 0.008(syst) ps(-1) and a decay width difference ΔΓ(s) ≡ Γ(L) - Γ(H) = 0.123 ± 0.029(stat) ± 0.011(syst) ps(-1). Our measurement is insensitive to the transformation (?(s),ΔΓ(s)) ? (π - ?(s), -ΔΓ(s)).     

Structural and magnetic dynamics of a laser induced phase transition in FeRh

We use time-resolved x-ray diffraction and magneto-optical Kerr effect to study the laser-induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (τ(1)~30 ps). This is significantly faster than the magnetic response (τ(2)~60 ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases coexist on short time scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented.     

Time resolved magnetization dynamics of ultrathin Fe(001) films: spin-pumping and two-magnon scattering

The time-resolved magnetic response of ultrathin epitaxial Fe(001) films grown on GaAs(001) and covered by Au, Pd, and Cr capping layers was investigated by time and spatially resolved Kerr effect measurements. The magnetization was excited by an in-plane magnetic field pulse using the transient internal field generated at a Schottky barrier while the wavelength of the excitation (resonant mode) was roughly 4 microm. Each of the three cap layers affected the spin relaxation in a unique way. Au cap layers resulted in the bulk Gilbert damping of the Fe film. Pd cap layers caused an additional Gilbert damping due to spin-pump or spin-sink effects. Cr cap layers lead to a strong extrinsic damping which can be described by two-magnon scattering. In this case the strength of the extrinsic damping can be controlled by a field induced shift of the spin wave manifold with respect to the excited k vector.     

Analysis of absorption enhancement in tailor‐made periodic polycrystalline silicon microarrays

We present a design study of 3D photonic poly‐Si microarchitectures on 2 µm periodically textured glass substrates for application as absorber layers in crystalline Si thin‐film solar cells. Different arrays of microholes and microcones were fabricated in a low‐cost process, by combining high rate electron beam evaporation, nanoimprint technology and self‐organized solid phase crystallization. Two promising designs exhibiting strong absorption enhancement were identified by optical analysis. High angular acceptance and calculated maximum achievable short‐circuit current density of 27.6 mA/cm² for an effective Si thickness of 1.1 µm highlight the optical potential of these microarchitectures as broadband absorbers in polycrystalline Si thin‐film solar cells.

     

Fluorescence of ammonia-d3 from its first excited singlet state

Structured emission spectra have been observed from ND₃ excited at 2139 Å and 2144 Å. The emission is short-lived (τ_{$\text{1}\text{2}$} < 10^?10 s) and has been assigned to the ND₃($\text{A}$) → ND₃($\text{X}$) fluorescence transition.     

Regiochemical switching in Diels-Alder cycloadditions by change in oxidation state of removable diene sulfur substituents. Synthesis of carbazoles by sequential heteroannulation and Diels-Alder cycloaddition

The palladium-catalyzed heteroannulation of N-carbobenzyloxy-o-iodoanilines with 1-phenylthio-1,3-butadiene afforded indolines 7, which were oxidized with DDQ to produce vinylogous 2-(phenylthio)indoles 8. The latter compounds underwent highly regioselective Diels-Alder cycloadditions with methyl propiolate in the presence of MeAlCl(2) or AlCl(3), with simultaneous elimination of benzenethiol, to afford methyl N-(carbobenzyloxy)carbazole-3-carboxylates 9 and, in some cases, the N-deprotected derivatives 11. This is the opposite regiochemistry of that observed previously with the corresponding sulfone analogues of 8. Thus, the regiochemistry of the cycloaddition can be effectively controlled by appropriate choice of oxidation state of the diene sulfur substituent.