Charge-transfer exciton in La2CuO4 probed with resonant inelastic x-ray scattering

We report a high-resolution resonant inelastic x-ray scattering study of La2CuO4. A number of spectral features are identified that were not clearly visible in earlier lower-resolution data. The momentum dependence of the spectral weight and the dispersion of the lowest energy excitation across the insulating gap have been measured in detail. The temperature dependence of the spectral features was also examined. The observed charge transfer edge shift, along with the low dispersion of the first charge transfer excitation are attributed to the lattice motion being coupled to the electronic system. In addition, we observe a dispersionless feature at 1.8 eV, which is associated with a d-d crystal field excitation.Comment: 5 pages, 4 figure

X-ray induced electronic structure change in CuIr2_2S4_4

The electronic structure of CuIr$_2$S$_4$ has been investigated using various bulk-sensitive x-ray spectroscopic methods near the Ir $L_3$-edge: resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy in the partial fluorescence yield (PFY-XAS) mode, and resonant x-ray emission spectroscopy (RXES). A strong RIXS signal (0.75 eV) resulting from a charge-density-wave gap opening is observed below the metal-insulator transition temperature of 230 K. The resultant modification of electronic structure is consistent with the density functional theory prediction. In the spin- and charge- dimer disordered phase induced by x-ray irradiation below 50 K, we find that a broad peak around 0.4 eV appears in the RIXS spectrum.Comment: 4 pages and 4 figure

Resonant inelastic X-ray scattering study of overdoped La2−x_{2-x}Srx_{x}CuO4_{4}

Resonant inelastic x-ray scattering (RIXS) at the copper K absorption edge has been performed for heavily overdoped samples of La$_{2-x}$Sr$_{x}$CuO$_{4}$ with $x= 0.25$ and 0.30. We have observed the charge transfer and molecular-orbital excitations which exhibit resonances at incident energies of $E_i= 8.992$ and 8.998 keV, respectively. From a comparison with previous results on undoped and optimally-doped samples, we determine that the charge-transfer excitation energy increases monotonically as doping increases. In addition, the $E_i$-dependences of the RIXS spectral weight and absorption spectrum exhibit no clear peak at $E_i = 8.998$ keV in contrast to results in the underdoped samples. The low-energy ($\leq 3$ eV) continuum excitation intensity has been studied utilizing the high energy resolution of 0.13 eV (FWHM). A comparison of the RIXS profiles at $(\pi ~0)$ and $(\pi ~\pi)$ indicates that the continuum intensity exists even at $(\pi ~\pi)$ in the overdoped samples, whereas it has been reported only at $(0 ~0)$ and $(\pi ~0)$ for the $x=0.17$ sample. Furthermore, we also found an additional excitation on top of the continuum intensity at the $(\pi ~\pi)$ and $(\pi ~0)$ positions.Comment: 7 pages, 7 figure

Peran Cagar Biosfer Cibodas Dalam Penyerapan Co 2

Cagar biosfer merupakan kawasan konservasi yang keberadaanya diakui secara Internasional sebagai suatu kawasan yang mempromosikan keseimbangan hubungan antara manusia dan lingkungan. Cagar biosfer memiliki 3 zona yakni zona inti sebagai kawasan konservasi, zona penyangga sebagai kawasan pelindung zona inti, serta zona transisi yang diperuntukan bagi kawasan pembangunan berkelanjutan. Cagar Biosfer Cibodas merupakan salah satu dari tujuh cagar biosfer yang ada di Indonesia dengan ekosistem terbesar hutan hujan pegunungan. Salah satu jasa lingkungan yang diberikan oleh Cagar Biosfer Cibodas adalah kemampuannya dalam penyerapan CO2 . Penelitian ini bertujuan untuk menduga nilai penyerapan CO2 di Cagar Biosfer Cibodas menggunakan nilai fluks karbon yang ditunjukkan oleh nilai (NPP). Hasil dari penelitian ini memberikan nilai fluks karbon tertinggi pada zona inti, zona penyangga dan zona transisi terjadi pada tahun 2006 yaitu berturut-turut sebesar 1.689,2 gC/m /tahun, 1.543,4 gC/m /tahun dan 1.197,3 gC/m /tahun. Potensi total penyerapan CO2 pada zona inti tertinggi terjadi pada tahun 1991 sebesar 1.473.572,4 ton/tahun, pada zona penyangga terjadi pada tahun 2006 sebesar 705.096,4 ton/tahun, dan pada zona transisi terjadi pada tahun 1991 sebesar 1.036.069,6 ton/tahun

Structural origin of the anomalous temperature dependence of the local magnetic moments in the CaFe2_{2}As2_{2} family of materials

We report a combination of Fe K$\beta$ x-ray emission spectroscopy and $ab$-intio calculations to investigate the correlation between structural and magnetic degrees of freedom in CaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$. The puzzling temperature behavior of the local moment found in rare earth-doped CaFe$_{2}$As$_{2}$ [\textit{H. Gretarsson, et al., Phys. Rev. Lett. {\bf 110}, 047003 (2013)}] is also observed in CaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$. We explain this phenomenon based on first-principles calculations with scaled magnetic interaction. One scaling parameter is sufficient to describe quantitatively the magnetic moments in both CaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ ($x=0.055$) and Ca$_{0.78}$La$_{0.22}$Fe$_{2}$As$_{2}$ at all temperatures. The anomalous growth of the local moments with increasing temperature can be understood from the observed large thermal expansion of the $c$-axis lattice parameter combined with strong magnetoelastic coupling. These effects originate from the strong tendency to form As-As dimers across the Ca layer in the CaFe$_{2}$As$_{2}$ family of materials. Our results emphasize the dual local-itinerant character of magnetism in Fe pnictides

Antibacterial activity in the blood cells of 'Carcinas maenas' (L.) and other crustaceans

In vitro antibacterial activity in the haemocytes of Carcinus maenas (L) was investigated. Haemocyte lysate supernatants (HLS) were assayed against twelve Gram-positive and Gram-negative marine bacteria, eight of which proved sensitive to the antibacterial factor or factors contained therein. Antibacterial activity was also found in HLS from four other marine crustaceans-Glyptonotus antarcticus, Galathea strigosa, Nephrops norvegicus and Crangon crangon. Activity in C. maenas HLS was independent of divalent cations, operated at high titre, was stable after treatment at 100 °C for 30 minutes and also after three months storage at -70 °C; it was present in the granular cells (which also contain the prophenoloxidase (proPO) activating system, a putative recognition mechanism in arthropods), but was absent from hyaline cells and plasma. In vitro studies were carried out to determine whether a relationship exists between the proPO system and the antibacterial activity in the haemocytes of C. maenas. It was shown that phenoloxidase and an activating serine protease were not responsible for the observed antimicrobial effects, although the possibility that activity resides with some other component of the proPO system has not been excluded. Seasonal variation in antibacterial activity, haemocyte counts and HLS protein concentrations was found, with conspicuous depression of antibacterial activity at two key points in the year. This occurred in conjunction with extremes of water temperature and it is proposed that the variation in antibacterial activity is due to underlying temperature effects on haemocyte counts and protein levels. Low levels of lytic activity against Micrococcus luteus cell walls and low levels of bacterial agglutination were recorded, but the powerful antibacterial activity in HLS could not be attributed to these alone. Gel filtration with Sephadex G-l00 revealed at least three antibacterial proteins of differing molecular size, with estimated MW of 72 kDa, 34 kDa and 4 kDa. The 72 kDa and 34 kDa proteins were bacteriostatic and the 4 kDa protein was bacteriolytic

Observation of a 500meV Collective Mode in La2−x_{2-x}Srx_xCuO4_4 and Nd2_2CuO4_4

Utilizing resonant inelastic x-ray scattering, we report a previously unobserved mode in the excitation spectrum of La$_{2-x}$Sr$_x$CuO$_4$ at 500 meV. The mode is peaked around the ($\pi$,0) point in reciprocal space and is observed to soften, and broaden, away from this point. Samples with x=0, 0.01, 0.05, and 0.17 were studied. The new mode is found to be rapidly suppressed with increasing Sr content and is absent at $x$=0.17, where it is replaced by a continuum of excitations. The peak is only observed when the incident x-ray polarization is normal to the CuO planes and is also present in Nd$_2$CuO$_4$. We suggest possible explanations for this excitation.Comment: 5 pages, 5 figure