Indications of coherence-incoherence crossover in layered transport

For many layered metals the temperature dependence of the interlayer resistance has a different behavior than the intralayer resistance. In order to better understand interlayer transport we consider a concrete model which exhibits this behavior. A small polaron model is used to illustrate how the interlayer transport is related to the coherence of quasi-particles within the layers. Explicit results are given for the electron spectral function, interlayer optical conductivity and the interlayer magnetoresistance. All these quantities have two contributions: one coherent (dominant at low temperatures) and one incoherent (dominant at high temperatures).Comment: 6 pages, 4 figures, REVTEX

Tunable local polariton modes in semiconductors

We study the local states within the polariton bandgap that arise due to deep defect centers with strong electron-phonon coupling. Electron transitions involving deep levels may result in alteration of local elastic constants. In this case, substantial reversible transformations of the impurity polariton density of states occur, which include the appearance/disappearance of the polariton impurity band, its shift and/or the modification of its shape. These changes can be induced by thermo- and photo-excitation of the localized electron states or by trapping of injected charge carriers. We develop a simple model, which is applied to the $O_P$ center in $GaP$. Further possible experimental realizations of the effect are discussed.Comment: 7 pages, 3 figure

Криптическое разнообразие рода Leucosolenia (Porifera: Calcarea) в Белом и Баренцевом морях

International audienceResults and discussion. Molecular analysis of two independent markers revealed eight monophyletic species-level lineages. Surprisingly, Leucosolenia complicata was found only in the NorthEast Atlantic, where it shows stable diagnostic morphological traits: tri-and tetractines with unpaired actines commonly longer than paired ones and the presence of both lanceolate diactines and small trichoxeas. In contrast, in the White sea Leucosolenia diversity is represented by a complex of three pseudo-cryptic species, which differ in external features, cytology, skeleton arrangement and spicule morphology. Leucosolenia sp. 1 is characterized by lanceolate diactines and T-shaped tri-and tetractines with unpaired actines commonly shorter than paired ones. Leucosolenia sp. 2 possess smooth and spined trichoxeas, which form prominent spicular crown around oscula and cover cormus tubes, making them hispid. In addition its tri-and tetractines are thin, many of them are abnormal. Tetractines are rare, presented only in oscular rim. Leucosolenia sp. 3 is easily distinguished by voluminous spherical cormus with one or several long oscular tubes, presence of lanceolate diactines and T-or V-shaped tri-and tetractines, some of which are abnormal. In addition, we found peculiar type of mesohyl cells with specific inclusions, occurring in large number. Leucosolenia sp. 1 and Leucosolenia sp. 2 are most common species in the White sea. In the upper intertidal zone they usually occurred sympatrically, while deeper waters are inhabited mostly by Leucosolenia sp. 1. Leucosolenia sp. 3 is also found in deep waters, but restricted to a single locality near Krestovye islands, which have specific fauna

Perceived complexity and distinct boundaries: a revision of calcareous sponge Leucosolenia complicata in the White Sea

International audienc