Suchergebnisse

HAL Id:hal-03396644 ; Two-dimensional molecular assemblies on surfaces have opened a way to design and control chirality, featuring promising electronic and chemical properties that depend on the local handedness of the layer. Yet, the mechanisms leading to spontaneous chiral resolution are not fully understood at every reaction stage. Here, starting from achiral 10-bromoanthracene-9-boronic acid as a molecular precursor, we demonstrate enantiomeric induction in products during the stage of covalent bonding, stemming from the competing point symmetries of the Ag(001)-supporting surface and the reaction products. Upon dehalogenation and dehydration of precursors, hexagonal boroxine rings linked by organometallic anthracene dimers are formed, which undergo a strong interaction with a fourfold symmetric substrate. The prochiral structural character of the resulting oligomer and its impact over the spatial distribution of the electronic molecular states are revealed by high-resolution scanning tunneling microscopy and spectroscopy. ; Financial support was provided by the European Union through Interreg-POCTEFA (Grant TNSI/EFA194/16) program, including EFRD funds, as well as by the Spanish Plan Nacional de I + D + i (MAT2016-78293-C6 and PID2019-107338RB-C6). We also acknowledge funding from Gobierno de Aragón (grupo de referencia E13_20R "NANOMIDAS") and Xunta de Galicia (Centro singular de investigación de Galicia, accreditation 2019-2022, ED431G 2019/03). ; Peer reviewed

The interaction among magnetic moments screened by conduction electrons drives quantum phase transitions between magnetically ordered and heavy-fermion ground states. Here, starting from isolated magnetic impurities in the Kondo regime, we investigate the formation of the finite size analogue of a heavy Fermi liquid. We build regularly-spaced chains of Co adatoms on a metallic surface by atomic manipulation. Scanning tunneling spectroscopy is used to obtain maps of the Kondo resonance intensity with sub-atomic resolution. For sufficiently small interatomic separation, the spatial distribution of Kondo screening does not coincide with the position of the adatoms. It also develops enhancements at both edges of the chains. Since we can rule out any other interaction between Kondo impurities, this is explained in terms of the indirect hybridization of the Kondo orbitals mediated by a coherent electron gas, the mechanism that causes the emergence of heavy quasiparticles in the thermodynamic limit. ; Financial support was provided by the Spanish Plan Nacional de I+D+i (grants MAT 2013-46593-C6-3-P, MAT2016-78293-C6-6-R, MAT2015-66888-C3-2-R, and FIS2015-64886-C5-3-P), Charles University (programme PRIMUS/Sci/09) and the European Union through programmes Interreg-POCTEFA (grant TNSI/EFA194/16) and H2020-EINFRA-5-2015 MaX Center of Excellence (grant no. 676598). M.M.-L., M.P., and D.S. acknowledge the use of SAI at Universidad de Zaragoza. R.R. acknowledges The Severo Ochoa Centers of Excellence Program (grant no. SEV-2017-0706) and Generalitat de Catalunya (grant no. 2017SGR1506 and the CERCA Programme). ; Peer reviewed

Recently, mixed honeycomb–kagome lattices featuring metal–organic networks have been theoretically proposed as topological insulator materials capable of hosting nontrivial edge states. This new family of so-called "organic topological insulators" are purely two-dimensional and combine polyaromatic-flat molecules with metal adatoms. However, their experimental validation is still pending given the generalized absence of edge states. Here, we generate one such proposed network on a Cu(111) substrate and study its morphology and electronic structure with the purpose of confirming its topological properties. The structural techniques reveal a practically flawless network that results in a kagome network multi-band observed by angle-resolved photoemission spectroscopy and scanning tunneling spectroscopy. However, at the network island borders we notice the absence of edge states. Bond-resolved imaging of the network exhibits an unexpected structural symmetry alteration that explains such disappearance. This collective lifting of the network symmetry could be more general than initially expected and provide a simple explanation for the recurrent experimental absence of edge states in predicted organic topological insulators. ; We gratefully acknowledge financial support from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant No. MAT2016-78293-C6-6-R, MAT2016-78293-C6-4-R and MAT2017-83468-R) and the Ministry of Science and Innovation (MICINN, Grant No. PID2019-107338RB-C6-3 and PID2019-107338RB-C6-4), from the regional Government of Aragon (E12-20R RASMIA project and Formación de Personal Investigador, 2018 grant) and the regional Government of the Basque Country (IT-1255-19), from the "Juan de la Cierva" program, and from the European Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (Contract No. EFA194/16 TNSI). C. D. is supported by the Royal Society University Research Fellowship (URF/R1/201158). ; We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). ; Peer reviewed