Ground state of the parallel double quantum dot system

We resolve the controversy regarding the ground state of the parallel double quantum dot system near half filling. The numerical renormalization group predicts an underscreened Kondo state with residual spin-1/2 magnetic moment, ln2 residual impurity entropy, and unitary conductance, while the Bethe ansatz solution predicts a fully screened impurity, regular Fermi-liquid ground state, and zero conductance. We calculate the impurity entropy of the system as a function of the temperature using the hybridization-expansion continuous-time quantum Monte Carlo technique, which is a numerically exact stochastic method, and find excellent agreement with the numerical renormalization group results. We show that the origin of the unconventional behavior in this model is the odd-symmetry "dark state" on the dots.     

Laser optoacoustic studies of intermolecular V-V processes: CH4/n-alkanes,and density of state aspects in V-V and E-V rates

Using laser excitation of CH₄ at 2947.9 cm^?1, V-V processes from the bending modes of CH₄ to deformation modes in a series of n-alkanes are studied optoacoustically. The results, like other V-V and E-V processes, show an incremental change in acceptor level density with the number of n-alkane C atoms.     

Chemical control of competing electron transfer pathways in iron tetracyano-polypyridyl photosensitizers

Photoinduced intramolecular electron transfer dynamics following metal-to-ligand charge-transfer (MLCT) excitation of [Fe(CN)₄(2,2′-bipyridine)]²⁻ (1), [Fe(CN)₄(2,3-bis(2-pyridyl)pyrazine)]²⁻ (2) and [Fe(CN)₄(2,2′-bipyrimidine)]²⁻ (3) were investigated in various solvents with static and time-resolved UV-Visible absorption spectroscopy and Fe 2p3d resonant inelastic X-ray scattering (RIXS). This series of polypyridyl ligands, combined with the strong solvatochromism of the complexes, enables the ¹MLCT vertical energy to be varied from 1.64 eV to 2.64 eV and the ³MLCT lifetime to range from 180 fs to 67 ps. The ³MLCT lifetimes in 1 and 2 decrease exponentially as the MLCT energy increases, consistent with electron transfer to the lowest energy triplet metal-centred (³MC) excited state, as established by the Tanabe–Sugano analysis of the Fe 2p3d RIXS data. In contrast, the ³MLCT lifetime in 3 changes non-monotonically with MLCT energy, exhibiting a maximum. This qualitatively distinct behaviour results from a competing ³MLCT → ground state (GS) electron transfer pathway that exhibits energy gap law behaviour. The ³MLCT → GS pathway involves nuclear tunnelling for the high-frequency polypyridyl breathing mode (hν = 1530 cm⁻¹), which is most displaced for complex 3, making this pathway significantly more efficient. Our study demonstrates that the excited state relaxation mechanism of Fe polypyridyl photosensitizers can be readily tuned by ligand and solvent environment. Furthermore, our study reveals that extending charge transfer lifetimes requires control of the relative energies of the ³MLCT and the ³MC states and suppression of the intramolecular distortion of the acceptor ligand in the ³MLCT excited state.

Photoinduced intramolecular electron transfer in Fe tetracyano-polypyridyl complexes was investigated with static and time-resolved UV-visible absorption and resonant inelastic X-ray scattering which revealed a competition of two relaxation pathways.     

Revealing the bonding of solvated Ru complexes with valence-to-core resonant inelastic X-ray scattering

Ru-complexes are widely studied because of their use in biological applications and photoconversion technologies. We reveal novel insights into the chemical bonding of a series of Ru(ii)- and Ru(iii)-complexes by leveraging recent advances in high-energy-resolution tender X-ray spectroscopy and theoretical calculations. We perform Ru 2p4d resonant inelastic X-ray scattering (RIXS) to probe the valence excitations in dilute solvated Ru-complexes. Combining these experiments with a newly developed theoretical approach based on time-dependent density functional theory, we assign the spectral features and quantify the metal–ligand bonding interactions. The valence-to-core RIXS features uniquely identify the metal-centered and charge transfer states and allow extracting the ligand-field splitting for all the complexes. The combined experimental and theoretical approach described here is shown to reliably characterize the ground and excited valence states of Ru complexes, and serve as a basis for future investigations of ruthenium, or other 4d metals active sites, in biological and chemical applications.

Combined experimental and theoretical Ru 2p4d resonant inelastic X-ray scattering study probes the chemical bonding and the valence excited states of solvated Ru complexes.     

Optimizing performance of plasmonic devices for photonic circuits

We demonstrate the feasibility of fabricating thermo-optic plasmonic devices for variable optical attenuation and/or low-frequency (kHz) signal modulation. Results of finite-element simulations and experimental characterization of prototype devices indicate that a plasmonic device can reach specifications similar to or better than commercially available thermo-optic integrated optical components. Specifically, we have considered the insertion loss, power consumption, footprint, polarization-dependent loss, extinction ratio, and frequency response of the plasmonic devices, in addition to fabrication and material-related issues. The most serious fabrication challenge is to realize metallic nanowire waveguides with a sufficiently accurate cross-section to ensure low polarization-dependent loss at high extinction ratios.     

Hot Branching Dynamics in a Light-Harvesting Iron Carbene Complex Revealed by Ultrafast X-ray Emission Spectroscopy

Iron N-heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub-ps X-ray spectroscopy study of an Fe^IINHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited molecules relax back to the ground state along two pathways: After population of a hot ³MLCT state, from the initially excited ¹MLCT state, 30 % of the molecules undergo ultrafast (150 fs) relaxation to the ³MC state, in competition with vibrational relaxation and cooling to the relaxed ³MLCT state. The relaxed ³MLCT state then decays much more slowly (7.6 ps) to the ³MC state. The ³MC state is rapidly (2.2 ps) deactivated to the ground state. The ⁵MC state is not involved in the deactivation pathway. The ultrafast partial deactivation of the ³MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen transition-metal complexes for similar ultrafast decays to optimize photochemical performance.     

Long-range dielectric-loaded surface plasmon polariton waveguides operating at telecommunication wavelengths

We report on the realization of long-range dielectric-loaded surface plasmon polariton waveguides (LR-DLSPPWs) consisting of straight and bent subwavelength dielectric ridges deposited on thin and narrow metal stripes supported by a dielectric buffer layer covering a low-index substrate. Using imaging with a near-field optical microscope and end-fire coupling with a tapered fiber connected to a tunable laser at telecommunication wavelengths (1425-1545?nm), we demonstrate low-loss (propagation length ～500?μm) and well-confined (mode width ～1?μm) LR-DLSPPW mode guiding and determine the propagation and bend loss.     

Is the resonance at 125 GeV the Higgs boson?

The recently discovered resonance at 125 GeV has properties remarkably close to those of the Standard Model Higgs boson. We perform model-independent fits of all presently available data. The non-standard best-fits found in our previous analyses remain favored with respect to the SM fit, mainly but not only because the γγ rate remains above the SM prediction.     

Bioactive components of the hop strobilus: comparison of different extraction methods by capillary electrophoretic and chromatographic methods

In the present study, the composition of the hop strobilus extract by using different extraction methods under different solvent conditions was analysed and compared. Several separation methods were applied to obtaining detailed information about the hop extract: capillary zone electrophoresis (CZE), high-performance liquid chromatography-mass-spectrometry (HPLC-MS/MS) and gas chromatography-mass-spectrometry (GC-MS). The electropherograms of different extracts varied dramatically. The oxidation reaction of the hop strobilus extract was examined.