Manipulation of the surface density of states of Ag(111) by means of resonators. Experiment and theory.

We show that the density of surface Shockley states of Ag(111) probed by the differential conductance G(V ) = d I /d V by a scanning-tunneling microscope (STM) can be enhanced significantly at certain energies and positions introducing simple arrays of Co or Ag atoms on the surface, in contrast to other noble-metal surfaces. Specifically we have studied resonators consisting of two parallel walls of five atoms deposited on the clean Ag(111) surface. A simple model in which the effect of the adatoms is taken into account by an attractive local potential and a small hybridization between surface and bulk at the position of the adatoms explains the main features of the observed G(V ) and allows us to extract the proportion of surface and bulk states sensed by the STM tip. These results might be relevant to engineer the surface spectral density of states, to study the effects of surface states on the Kondo effect, and to separate bulk and surface contributions in STM studies of topological surface states

Real space manifestations of coherent screening in atomic scale Kondo lattices

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)

Publisher Correction : Real space manifestations of coherent screening in atomic scale Kondo lattices

Aquesta és una correcció a l'article 10.1038/s41467-019-10103-

Influence of shockley surface state in the Kondo resonance of Co adatoms on Ag(111)

Resumen del trabajo presentado a la 10th Conferencia Fuerzas y Túnel, celebrada en Girona (España) del 5 al 7 de septiembre de 2016.-- et al.The magnetic properties of magnetic atoms on metals are inherently connected with many body interactions between the localized magnetic moments and the supporting surface. This is because the electronic orbitals of atoms couple with the continuum of conduction electrons of the metal host. But this influence is reciprocal, since the properties of the substrate also change locally due to the presence of an atom. The understanding of the behavior of the spin moments of the atoms on a metal surface is one of the pillars of spintronics for the development of prototypes at the atomic scale. In particular, the study of the Kondo resonance appearing under particular conditions when a magnetic adatom lies on a metal surface provides deep insight into the involved magnetic interactions. We have chosen Co/Ag(111) as a model system to study the influence of the host LDOS in the Kondo effect of Co atoms. Combining STS and lateral manipulation techniques, we have carried out a study of the Kondo resonance as a function of the contacting lead LDOS of the Ag(111) surface with accurate control of the Co position. This has enabled us to probe a high degree of inhomogeneity in the surface state of Ag(111). Here we unambiguously identify the relevant contribution of surface state electrons to the relevant energy scale of the many-body Kondo sate (the Kondo temperature TK), in contrast to other previous works. This entails that the coupling strength between a magnetic impurity and its foremost environment can be tuned through the electronic properties of the metal host, leading to important fundamental and technological implications.Peer reviewe

RAW DATA: Real space manifestations of coherent screening in atomic scale Kondo lattices

Supporting raw data for the article entitled "Real space manifestations of coherent screening in atomic scale Kondo lattices", to be accepted by Nature CommunicationsFinancial 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). MML, MP and DS acknowledge the use of SAI at Universidad de Zaragoza. RR 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 reviewe

Real space manifestations of coherent screening in atomic scale Kondo lattices

Altres ajuts: CERCA Programme/Generalitat de CatalunyaThe 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

Characterization of 2D-assembled overlayers based on p-aminophenol on Cu(110)

Trabajo presentado en el International Workshop On-surface Synthesis, celebrado en San Sebastián del 27 al 30 de junio de 2016.On-surface chemistry has emerged as an important research field leading to unconventional self-assembled nanoarchitectures with tunable properties [1,2]. The development of surfacesensitive spectroscopies has provided a powerful set of tools for a detailed characterization of the structure, composition, and physicochemical properties of the molecular structures obtained by this methodology. We have evaporated p-aminophenol (p-AP) on Cu(110) at 493 K and followed a bottom-up azocoupling reaction, leading to dimer formation: 4,4'-azobis(phenol). We have characterized the on-surface synthesized self-assembled structure by different techniques. Thus, by using a combination of STM/AFM, LEED, XPS and NEXAFS as well as DFT calculations, we are able to unveil the structural and chemical characteristics of the process and outcome. The structural analysis reveals that p-AP molecules have coupled forming new molecular species that self-organize on the surface. They lay in a flat geometry preserving the in-plane ¿- conjugated benzene units as depicted by NEXAFS. LEED pattern analysis shows that the molecular layer exhibit a long-range order with a [(5,1),(-1,2)] symmetry, forming chains rotated 20º with respect to the [001] direction of the Cu surface, as deduced by the STM/AFM images. (Fig 1). Finally, the XPS N1s spectra reveal an oxidation reaction from amine to imine while XPS O1s data suggests that oxygen atoms are covalently bound to the substrate. In summary, all the information obtained by following this multitechnique study, allow us to figure out a model of the structure promoted by the catalytic properties of substrate in a thermal activated process.N

Chemical Disorder in Topological Insulators: A Route to Magnetism Tolerant Topological Surface States

We show that the chemical inhomogeneity in ternary three-dimensional topological insulators preserves the topological spin texture of their surface states against a net surface magnetization. The spin texture is that of a Dirac cone with helical spin structure in the reciprocal space, which gives rise to spin-polarized and dissipation-less charge currents. Thanks to the nontrivial topology of the bulk electronic structure, this spin texture is robust against most types of surface defects. However, magnetic perturbations break the time-reversal symmetry, enabling magnetic scattering and loss of spin coherence of the charge carriers. This intrinsic incompatibility precludes the design of magnetoelectronic devices based on the coupling between magnetic materials and topological surface states. We demonstrate that the magnetization coming from individual Co atoms deposited on the surface can disrupt the spin coherence of the carriers in the archetypal topological insulator Bi₂Te₃, while in Bi₂Se₂Te the spin texture remains unperturbed. This is concluded from the observation of elastic backscattering events in quasiparticle interference patterns obtained by scanning tunneling spectroscopy. The mechanism responsible for the protection is investigated by energy resolved spectroscopy and ab initio calculations, and it is ascribed to the distorted adsorption geometry of localized magnetic moments due to Se–Te disorder, which suppresses the Co hybridization with the surface states

Chemical Disorder in Topological Insulators: A Route to Magnetism Tolerant Topological Surface States

We show that the chemical inhomogeneity in ternary three-dimensional topological insulators preserves the topological spin texture of their surface states against a net surface magnetization. The spin texture is that of a Dirac cone with helical spin structure in the reciprocal space, which gives rise to spin-polarized and dissipation-less charge currents. Thanks to the nontrivial topology of the bulk electronic structure, this spin texture is robust against most types of surface defects. However, magnetic perturbations break the time-reversal symmetry, enabling magnetic scattering and loss of spin coherence of the charge carriers. This intrinsic incompatibility precludes the design of magnetoelectronic devices based on the coupling between magnetic materials and topological surface states. We demonstrate that the magnetization coming from individual Co atoms deposited on the surface can disrupt the spin coherence of the carriers in the archetypal topological insulator Bi2Te3, while in Bi2Se2Te the spin texture remains unperturbed. This is concluded from the observation of elastic backscattering events in quasiparticle interference patterns obtained by scanning tunneling spectroscopy. The mechanism responsible for the protection is investigated by energy resolved spectroscopy and ab initio calculations, and it is ascribed to the distorted adsorption geometry of localized magnetic moments due to Se–Te disorder, which suppresses the Co hybridization with the surface states.This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see DOI: 10.1021/acs.nanolett.7b00311. Posted with permission.</p