In this study, we report production, isolation, and characterization for the relatively small endohedral metallofullerene, La 2 @C 72. As described, La 2 @C 72 is readily isolated from conventional electric-arc-generated carbon/metal soot. This new species was purified by HPLC chromatography and characterized by laser desorption mass spectrometry and UV-vis spectroscopy. The mass spectrum also demonstrates the presence of the monometal species, La@C 72 , but the absence of empty-cage C 72. Since empty-cage C 72 has not been successfully isolated to date, the results of the present study are in agreement with the argument for metalmediated stabilization of the C 72 carbon cage by lanthanum ions. The chromatographic retention data suggest that the electronic structure of La 2 @C 72 is consistent with a (La 3+) 2 @C 72 6species and the prediction of a relatively small dipole moment.

Charge-transfer complexes of conjugated polymers as intermediates in charge photogeneration for organic photovoltaics Bakulin, Artem A.; Martyanov, Dmitry; Paraschuk, Dmitry Yu.; van Loosdrecht, Paul H. M.; Pshenichnikov, Maxim S. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Ultrafast visible-pump/IR-probe spectroscopy is applied to study the wavelength dependence of charge photogeneration in materials based on donor-acceptor charge-transfer complexes (CTCs) of the conjugated polymer MEH-PPV. In binary polymer-acceptor blends, photoexcitation in the absorption band of either CTC or polymer results in similar dynamics of the charge-associated transient absorption. Likewise, in polymer/CTC-acceptor/fullerene ternary blends, where charge separation occurs via a two-step pathway, the photophysics is also independent of excitation wavelength. These similarities in charge dynamics indicate that CTC excited states serve as an intermediate for charge photogeneration. The conclusions of the ultrafast study are supported by photocurrent spectroscopy.

In the quest for realizations of quantum spin liquids, the exploration of Kitaev materials -spin-orbit entangled Mott insulators with strong bond-directional exchanges -has taken center stage. However, in these materials the local spin-orbital j = 1/2 moments typically show long-range magnetic order at low temperature, thus defying the formation of a spin-liquid ground state. Using resonant inelastic x-ray scattering (RIXS), we here report on a proximate spin liquid regime with clear fingerprints of Kitaev physics in the magnetic excitations of the honeycomb iridates α-Li2IrO3 and Na2IrO3. We observe a broad continuum of magnetic excitations that persists up to at least 300 K, more than an order of magnitude larger than the magnetic ordering temperatures. We prove the magnetic character of this continuum by an analysis of the resonance behavior. RIXS measurements of the dynamical structure factor for energies within the continuum show that dynamical spin-spin correlations are restricted to nearest neighbors. Notably, these spectroscopic observations are also present in the magnetically ordered state for excitation energies above the conventional magnon excitations. Phenomenologically, our data agree with inelastic neutron scattering results on the related honeycomb compound α-RuCl3, establishing a common ground for a proximate Kitaev spin-liquid regime in these materials.

The honeycomb compound α-RuCl 3 is widely discussed as a proximate Kitaev spin-liquid material. This scenario builds on spin-orbit entangled j = 1/2 moments arising for a t 5 2g electron configuration with strong spin-orbit coupling λ and a large cubic crystal field. The actual low-energy electronic structure of α-RuCl 3 , however, is still puzzling. In particular, infrared absorption features at 0.30, 0.53, and 0.75 eV seem to be at odds with a j = 1/2 scenario. Also the energy of the spin-orbit exciton, the excitation from j = 1/2 to 3/2, and thus the value of λ, are controversial. Combining infrared and Raman data, we show that the infrared features can be attributed to single, double, and triple spin-orbit excitons. We find λ = 0.16 eV and = 42(4) meV for the observed noncubic crystal-field splitting, supporting the validity of the j = 1/2 picture for α-RuCl 3. The unusual strength of the double excitation is related to the underlying hopping interactions, which form the basis for dominant Kitaev exchange.

The cover picture of this issue of Phys. Status Solidi C has been taken from the article [1]. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)