Electronic structure of one-dimensional copper oxide chains in LiCu2O2 from angle-resolved photoemission and optical spectroscopy

Angle-resolved photoemission (ARPES) and optical measurements were performed on single crystal samples of LiCu2O2, an antiferromagnetic S=1/2 spin-chain compound. The ARPES spectra show several dispersive branches associated with hybrid copper-oxygen states. The occurrence of the valence band maximum halfway between the center and the edge of the Brillouin zone, and the complex spectral line shapes are not reproduced by the existing calculations of the electronic structure. We suggest that they can be interpreted within a one-dimensional scenario of strongly correlated antiferromagnetic insulators. The combination of ARPES and optics allows us to estimate the magnitude of the charge-transfer gap (Delta=1.95 eV). Moreover, the temperature-dependent optical conductivity bears signatures of the three different magnetic phases of this material

Near-edge x-ray absorption fine structure investigation of graphene

We report the near-edge x-ray absorption fine structure (NEXAFS) spectrum of a single layer of graphite (graphene) obtained by micromechanical cleavage of Highly Ordered Pyrolytic Graphite (HOPG) on a SiO2 substrate. We utilized a PhotoEmission Electron Microscope (PEEM) to separately study single- double- and few-layers graphene (FLG) samples. In single-layer graphene we observe a splitting of the pi* resonance and a clear signature of the predicted interlayer state. The NEXAFS data illustrate the rapid evolution of the electronic structure with the increased number of layers.Comment: 5 pages, 4 figure

Linking working memory and long-term memory: A computational model of the learning of new words

The nonword repetition (NWR) test has been shown to be a good predictor of children’s vocabulary size. NWR performance has been explained using phonological working memory, which is seen as a critical component in the learning of new words. However, no detailed specification of the link between phonological working memory and long-term memory (LTM) has been proposed. In this paper, we present a computational model of children’s vocabulary acquisition (EPAM-VOC) that specifies how phonological working memory and LTM interact. The model learns phoneme sequences, which are stored in LTM and mediate how much information can be held in working memory. The model’s behaviour is compared with that of children in a new study of NWR, conducted in order to ensure the same nonword stimuli and methodology across ages. EPAM-VOC shows a pattern of results similar to that of children: performance is better for shorter nonwords and for wordlike nonwords, and performance improves with age. EPAM-VOC also simulates the superior performance for single consonant nonwords over clustered consonant nonwords found in previous NWR studies. EPAM-VOC provides a simple and elegant computational account of some of the key processes involved in the learning of new words: it specifies how phonological working memory and LTM interact; makes testable predictions; and suggests that developmental changes in NWR performance may reflect differences in the amount of information that has been encoded in LTM rather than developmental changes in working memory capacity. Keywords: EPAM, working memory, long-term memory, nonword repetition, vocabulary acquisition, developmental change

P16-17. Antigen sensitivity is a major determinant of CD8+ T-cell polyfunctionality and HIV suppressive activity

International audiencen.

Object-action dissociation : a voxel-based lesion-symptom mapping study on 102 patients after glioma removal

Data concerning the neural basis of noun and verb processing are inconsistent. Some authors assume that action-verb processing is based on frontal areas while nouns processing relies on temporal regions; others argue that the circuits processing verbs and nouns are closely interconnected in a predominantly left-lateralized fronto-temporal-parietal network; yet, other researchers consider that the primary motor cortex plays a crucial role in processing action verbs. In the present study, one hundred and two patients with a tumour either in the right or left hemisphere were submitted to picture naming of objects and actions before and after surgery. To test the effect of specific brain regions in object and action naming, patients' lesions were mapped and voxel-lesion-symptom mapping (VLSM) was computed. Behavioural results showed that left-brain damaged patients were significantly more impaired than right brain-damaged patients. The VLSM showed that these two grammatical classes are segregated in the left hemisphere. In particular, scores in naming of objects correlated with damage to the anterior temporal region, while scores in naming of actions correlated with lesions in the parietal areas and in the posterior temporal cortex. In addition, VLSM analyses carried out on non-linguistic tasks were not significant, confirming that the regions associated with deficits in object and action naming were not generally engaged in all cognitive tasks. Finally, the involvement of subcortical pathways was investigated and the inferior longitudinal fasciculus proved to play a role in object naming, while no specific bundle was identified for actions

On the floating of the topological surface state on top of a thick lead layer: The case of the Pb/Bi2Se3 interface

The puzzling question about the floating of the topological surface state on top of a thick Pb layer, has now possibly been answered. A study of the interface made by Pb on Bi2Se3 for different temperature and adsorbate coverage condition, allowed us to demonstrate that the evidence reported in the literature can be related to the surface diffusion phenomenon exhibited by the Pb atoms, which leaves the substrate partially uncovered. Comprehensive density functional theory calculations show that despite the specific arrangement of the atoms at the interface, the topological surface state cannot float on top of the adlayer but rather tends to move inward within the substrate.Comment: 9 pages, 5 figure

Electronic band structure of three-dimensional topological insulators with different stoichiometry composition

We report on a comparative theoretical and experimental investigation of the electronic band structure of a family of three-dimensional topological insulators, AIVBi4Te7−xSex (AIV= Sn, Pb;x = 0, 1). We prove by means of density functional theory calculations and angle-resolved photoemission spectroscopy measurements that partial or total substitution of heavy atoms by lighter isoelectronic ones affects the electronic properties of topological insulators. In particular, we show that the modification of the Dirac cone position relative to the Fermi level and the bulk band gap size can be controlled by varying the stoichiometry of the compound. We also demonstrate that the investigated systems are inert to oxygen exposure.The authors acknowledge financial support from the Saint Petersburg State University (Grant No. 40990069), the Tomsk State University competitiveness improvement program (Grant No. 8.1.01.2018), the Fundamental Research Program of the State Academies of Sciences (line of research III.23.2.9), and the project EUROFEL-ROADMAP ESFRI. This work was also partly supported by the Italian Ministry of Education, Universities and Research (MIUR) through project PON03PE_00092_1 (EOMAT) and by the Science Development Foundation under the President of the Republic of Azerbaijan (Grant No. EIF/MQM/Elm-Tehsil-1-2016- 1(26)-71/01/4-M-33). S.V.E. acknowledges support from the Russian Science Foundation (Grant No. 18-12-00169) for part of the electronic band structure calculations.Peer reviewe

One-dimensional Rashba states with unconventional spin texture in Bi chains

Spin-polarized electrons confined in low-dimensional structures are of high interest for spintronics applications. Here, we investigate the electronic structure of an ordered array of Bi monomer and dimer chains on the Ag(110) surface. By means of spin-resolved photoemission spectroscopy, we find Rashba-Bychkov split bands crossing the Fermi level with one-dimensional constant energy contours. These bands are up-spin polarized for positive wave vectors and down-spin polarized for negative wave vectors, at variance with the Rashba-Bychkov model that predicts a pair of states with opposite spin in each half of the surface Brillouin zone. Density functional theory shows that spin-selective hybridization with the Ag bulk bands originates this unconventional spin texture