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1. Electron delocalization in a 2D Mott insulator

Author

Ayani, Cosme G., Pisarra, Michele, Ibarburu, Iván M., Rebanal, Clara, Garnica, Manuela, Calleja, Fabián, Martín, Fernando, and de Parga, Amadeo L. Vázquez

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

The prominent role of electron-electron interactions in two-dimensional (2D) materials versus three-dimensional (3D) ones is at the origin of the great variety of fermionic correlated states reported in the literature. In this respect, artificial van der Waals heterostructures comprising single layers of highly correlated insulators allow one to explore the effect of the subtle interlayer interaction in the way electrons correlate. In this work, we study the temperature dependence of the electronic properties of a van der Waals heterostructure composed of a single-layer Mott insulator lying on a metallic substrate by performing quasi-particle interference (QPI) maps. We show the emergence of a Fermi contour in the 2D Mott insulator at temperatures below 11K, which we attribute to the delocalization of the Mott electrons associated with the formation of a quantum coherent Kondo lattice. This Kondo lattice introduces a new periodicity in the system, so that the resulting Fermi surface encompasses both the substrate conduction electrons and the now delocalized correlated electrons from the 2D Mott insulator. Density Functional Theory calculations allow us to pinpoint the scattering vectors responsible for the experimentally observed quasi-particle interference maps, thus providing a complete picture of the delocalization of highly correlated electrons in a 2D Mott insulator., Comment: 15 pages, 4 figures

Published
2024

2. Metastable polymorphic phases in monolayer TaTe2

Author

Di Bernardo, Iolanda, Ripoll-Sau, Joan, Calleja, Fabian, Ayani, Cosme G., Miranda, Rodolfo, Silva-Guillen, Jose Angel, Canadell, Enric, Garnica, Manuela, and de Parga, Amadeo L. Vazquez

Subjects
Condensed Matter - Materials Science
Abstract

Polymorphic phases and collective phenomena - such as charge density waves (CDWs) - in transition metal dichalcogenides (TMDs) dictate the physical and electronic properties of the material. Most TMDs naturally occur in a single given phase, but the fine-tuning of growth conditions via methods like molecular beam epitaxy (MBE) allows to unlock otherwise inaccessible polymorphic structures. Exploring and understanding the morphological and electronic properties of new phases of TMDs is an essential step to enable their exploitation in technological applications. Here, we use scanning tunneling microscopy to map MBE-grown monolayer TaTe2. We report the first observation of the 1H polymorphic phase, coexisting with the 1T, and demonstrate that their relative coverage can be controlled by adjusting synthesis parameters. Several super-periodic structures, compatible with CDWs, are observed to coexist on the 1T phase. Finally, we provide theoretical insight on the delicate balance between Te...Te and Ta-Ta interactions that dictates the stability of the different phases. Our findings demonstrate that TaTe2 is an ideal platform to investigate competing interactions, and indicate that accurate tuning of growth conditions is key to accessing metastable states in TMDs.

Published
2023
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3. Switchable molecular functionalization of an STM tip: from a Yu-Shiba-Rusinov tip to a Kondo tip

Author

Ayani, Cosme. G., Calleja, Fabian, Ibarburu, Ivan M., Casado, Pablo, Nazriq, Nana K. M., Yamada, Toyo. K., Garnica, Manuela., de Parga, Amadeo L. Vázquez, and Miranda, Rodolfo

Subjects
Physics - Applied Physics, Condensed Matter - Superconductivity
Abstract

In this work we fabricate and characterize a functionalized superconducting (SC) Nb tip of a scanning tunnelling microscope (STM). The tip is functionalized with a Tetracyanoquinodimethane molecule (TCNQ) that accepts charge from the tip and develops a magnetic moment. As a consequence, in scanning tunnelling spectroscopy (STS), sharp, bias symmetric sub-gap states identified as Yu-Shiba-Rusinov (YSR) bound states appear against the featureless density of states of a metallic gr/Ir(111) sample. Although the coupling regime of the magnetic impurity with the SC tip depends on the initial absorption configuration of the molecule, the interaction strength between the superconducting tip and the charged TCNQ molecule can be reversibly controlled by tuning the tip-sample distance. The controlled transition from one coupling regime to the other allows us to verify the relation between the energy scales of the two competing many-body effects for the functionalized tip. Quenching the SC state of the Nb tip with a magnetic field switches abruptly from a tip dominated by the YSR bound states to a Kondo tip.

Published
2022

4. Probing the phase transition to a coherent 2D Kondo lattice

Author

Ayani, Cosme G., Pisarra, Michele, Ibarburu, Iván M., Garnica, Manuela, Miranda, Rodolfo, Calleja, Fabián, Martín, Fernando, and de Parga, Amadeo L. Vázquez

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Strongly correlated materials exhibit exotic electronic states arising from the strong correlation between electrons. Dimensionality provides a tuning knob because thinning down to atomic thickness reduces screening effects and enhances electron correlations. In this work, a 2D Kondo lattice has been created by stacking a layer of 1T-TaS2 on a 2H-TaS2 crystal, which are bound by weak van der Waals interactions. By using high-resolution scanning tunnelling spectroscopy and density functional theory, we unambiguously demonstrate the formation of a 2D Kondo lattice from an ensemble of independent Kondo impurities present at higher temperatures. The possibility to create 2D Kondo lattices in van der Waals heterostructures paves the way for the exploration of unconventional metallic, magnetic and superconducting states not present in more standard correlated materials.

Published
2022
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6. Graphene grown on transition metal substrates: Versatile templates for organic molecules with new properties and structures

Author

Díaz, Cristina, Calleja, Fabián, Vázquez de Parga, Amadeo L., Martín, Fernando, Díaz, Cristina, Calleja, Fabián, Vázquez de Parga, Amadeo L., and Martín, Fernando

Abstract

The interest in graphene (a carbon monolayer) adsorbed on metal surfaces goes back to the 60’s, long before isolated graphene was produced in the laboratory. Owing to the carbon-metal interaction and the lattice mismatch between the carbon monolayer and the metal surface, graphene usually adopts a rippled structure, known as moir´e, that confers it interesting electronic properties not present in isolated graphene. These moir´e structures can be used as versatile templates where to adsorb, isolate and assemble organic-molecule structures with some desired geometric and electronic properties. In this review, we first describe the main experimental techniques and the theoretical methods currently available to produce and characterize these complex systems. Then, we review the diversity of moiré structures that have been reported in the literature and the consequences for the electronic properties of graphene, attending to the magnitude of the lattice mismatch and the type of interaction, chemical or physical, between graphene and the metal surface. Subsequently, we address the problem of the adsorption of single organic molecules and then of several ones, from dimers to complete monolayers, describing both the different arrangements that these molecules can adopt as well as their physical and chemical properties. We pay a special attention to graphene/Ru(0001) due to its exceptional electronic properties, which have been used to induce long-range magnetic order in tetracyanoquinodimethane (TCNQ) monolayers, to catalyze the (reversible) reaction between acetonitrile and TCNQ molecules and to efficiently photogenerate large acenes., MICINN, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Published
2024

7. Metastable Polymorphic Phases in Monolayer TaTe2

Author

Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Ciencia e Innovación (España), Comunidad de Madrid, Agencia Estatal de Investigación (España), ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Generalitat de Catalunya, Bernardo, Iolanda Di [0000-0002-2364-5544], Silva-Guillén, Jose Ángel [0000-0002-0483-5334], Calleja, Fabián [0000-0001-6007-8641], Miranda, Rodolfo [0000-0002-1064-6724], Canadell, Enric [0000-0002-4663-5226], Garnica, Manuela [0000-0002-7861-9490], Vázquez de Parga, Amadeo L. [0000-0003-0551-1603], Bernardo, Iolanda Di, Ripoll Sau, Joan, Silva-Guillén, Jose Ángel, Calleja, Fabián, Ayani, Cosme G., Miranda, Rodolfo, Canadell, Enric, Garnica, Manuela, Vázquez de Parga, Amadeo L., Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Ciencia e Innovación (España), Comunidad de Madrid, Agencia Estatal de Investigación (España), ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Generalitat de Catalunya, Bernardo, Iolanda Di [0000-0002-2364-5544], Silva-Guillén, Jose Ángel [0000-0002-0483-5334], Calleja, Fabián [0000-0001-6007-8641], Miranda, Rodolfo [0000-0002-1064-6724], Canadell, Enric [0000-0002-4663-5226], Garnica, Manuela [0000-0002-7861-9490], Vázquez de Parga, Amadeo L. [0000-0003-0551-1603], Bernardo, Iolanda Di, Ripoll Sau, Joan, Silva-Guillén, Jose Ángel, Calleja, Fabián, Ayani, Cosme G., Miranda, Rodolfo, Canadell, Enric, Garnica, Manuela, and Vázquez de Parga, Amadeo L.

Abstract

Polymorphic phases and collective phenomena-such as charge density waves (CDWs)-in transition metal dichalcogenides (TMDs) dictate the physical and electronic properties of the material. Most TMDs naturally occur in a single given phase, but the fine-tuning of growth conditions via methods such as molecular beam epitaxy (MBE) allows to unlock otherwise inaccessible polymorphic structures. Exploring and understanding the morphological and electronic properties of new phases of TMDs is an essential step to enable their exploitation in technological applications. Here, scanning tunneling microscopy (STM) is used to map MBE-grown monolayer (ML) TaTe2 . This work reports the first observation of the 1H polymorphic phase, coexisting with the 1T, and demonstrates that their relative coverage can be controlled by adjusting synthesis parameters. Several superperiodic structures, compatible with CDWs, are observed to coexist on the 1T phase. Finally, this work provides theoretical insight on the delicate balance between Te…Te and Ta-Ta interactions that dictates the stability of the different phases. The findings demonstrate that TaTe2 is an ideal platform to investigate competing interactions, and indicate that accurate tuning of growth conditions is key to accessing metastable states in TMDs.

Published
2023

8. Two Distinct Phases of Bilayer Graphene Films on Ru(0001)

Author

Papagno, Marco, Pacilé, Daniela, Topwal, Dinesh, Moras, Paolo, Sheverdyaeva, Polina Makarovna, Natterer, Fabian Donat, Lehnert, Anne, Rusponi, Stefano, Dubout, Quentin, Calleja, Fabian, Frantzeskakis, Emmanouil, Pons, Stéphane, Fujii, Jun, Vobornik, Ivana, Grioni, Marco, Carbone, Carlo, and Brune, Harald

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

By combining angle-resolved photoemission spectroscopy and scanning tunneling microscopy we reveal the structural and electronic properties of multilayer graphene on Ru(0001). We prove that large ethylene exposure allows to synthesize two distinct phases of bilayer graphene with different properties. The first phase has Bernal AB stacking with respect to the first graphene layer, displays weak vertical interaction and electron doping. The long-range ordered moir\'e pattern modulates the crystal potential and induces replicas of the Dirac cone and minigaps. The second phase has AA stacking sequence with respect to the first layer, displays weak structural and electronic modulation and p-doping. The linearly dispersing Dirac state reveals the nearly-freestanding character of this novel second layer phase.

Published
2013
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12. Probing the Phase Transition to a Coherent 2D Kondo Lattice

Author

Ayani C.G., Pisarra M., Ibarburu I.M., Garnica, Manuela, Miranda, Rodolfo, Calleja, Fabián, Martín, Fernando, Vázquez de Parga A.L., Ayani C.G., Pisarra M., Ibarburu I.M., Garnica, Manuela, Miranda, Rodolfo, Calleja, Fabián, Martín, Fernando, and Vázquez de Parga A.L.

Published
2023

13. Efficient photogeneration of nonacene on nanostructured graphene

Author

Ayani, Cosme G., Pisarra, Michele, Urgel, José I., Navarro, Juan Jesús, Díaz, Cristina, Hayashi, Hironobu, Yamada, Hiroko, Calleja, Fabián, Miranda, Rodolfo, Fasel, Román, Martín, Fernando, Vázquez de Parga, Amadeo L., Ayani, Cosme G., Pisarra, Michele, Urgel, José I., Navarro, Juan Jesús, Díaz, Cristina, Hayashi, Hironobu, Yamada, Hiroko, Calleja, Fabián, Miranda, Rodolfo, Fasel, Román, Martín, Fernando, and Vázquez de Parga, Amadeo L.

Abstract

The on-surface photogeneration of nonacene from a-bisdiketone precursors deposited on nanostructured epitaxial graphene grown on Ru(0001) has been studied by means of low temperature scanning tunneling microscopy and spectroscopy. The presence of an unoccupied surface state, spatially localized in the regions where the precursors are adsorbed, and energetically accessible in the region of the electromagnetic spectrum where n–p* transitions take place, allows for a 100% conversion of the precursors into nonacenes. With the help of state-of-the-art theoretical calculations, we show that such a high yield is due to the effective population of the surface state by the incoming light and the ensuing electron transfer to the unoccupied states of the precursors through an inelastic scattering mechanism. Our findings are the experimental confirmation that surface states can play a prominent role in the surface photochemistry of complex molecular systems, in accordance with early theoretical predictions made on small molecules., MICINN, MINECO, Comunidad de Madrid, Swiss National Science Foundation, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Published
2023

17. Atomic-scale study of type-II Dirac semimetal PtTe2surface

Author

Casado Aguilar P., Calleja, Fabián, Kuo C.-N., Lue C.S., Ghosh B., Agarwal A., Politano A., Vázquez de Parga, Amadeo L., Miranda, Rodolfo, Silva-Guillén, José Ángel, Garnica, Manuela, Casado Aguilar P., Calleja, Fabián, Kuo C.-N., Lue C.S., Ghosh B., Agarwal A., Politano A., Vázquez de Parga, Amadeo L., Miranda, Rodolfo, Silva-Guillén, José Ángel, and Garnica, Manuela

Published
2022

19. Two-dimensional Kondo lattice in a TaS2 van der Waals heterostructure

Author

Ayani, Cosme G., Pisarra, Michele, Ibarburu, Iván M., Garnica, Manuela, Miranda, Rodolfo, Calleja, Fabián, Martín, Fernando, and de Parga, Amadeo L. Vázquez

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics, Strongly Correlated Electrons (cond-mat.str-el), Mesoscale and Nanoscale Physics (cond-mat.mes-hall), Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences, Condensed Matter::Strongly Correlated Electrons, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect
Abstract

Strongly correlated materials exhibit exotic electronic states arising from the strong correlation between electrons. Dimensionality provides a tuning knob because thinning down to atomic thickness reduces screening effects and enhances electron correlations. In this work, a 2D Kondo lattice has been created by stacking a layer of 1T-TaS2 on a 2H-TaS2 crystal, which are bound by weak van der Waals interactions. By using high-resolution scanning tunnelling spectroscopy and density functional theory, we unambiguously demonstrate the formation of a 2D Kondo lattice from an ensemble of independent Kondo impurities present at higher temperatures. The possibility to create 2D Kondo lattices in van der Waals heterostructures paves the way for the exploration of unconventional metallic, magnetic and superconducting states not present in more standard correlated materials.

Published
2022
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20. Efficient photogeneration of nonacene on nanostructured graphene

Author

Ayani C.G., Pisarra M., Urgel J.I., Navarro J.J., Díaz C., Hayashi H., Yamada H., Calleja, Fabián, Miranda, Rodolfo, Fasel R., Martín, Fernando, Vázquez de Parga, Amadeo L., Ayani C.G., Pisarra M., Urgel J.I., Navarro J.J., Díaz C., Hayashi H., Yamada H., Calleja, Fabián, Miranda, Rodolfo, Fasel R., Martín, Fernando, and Vázquez de Parga, Amadeo L.

Published
2021

21. Electron–phonon coupling in superconducting 1T-PdTe2

Author

Anemone G., Casado Aguilar P., Garnica, Manuela, Calleja, Fabián, Al Taleb A., Kuo C.-N., Lue C.S., Politano A., Vázquez de Parga, Amadeo L., Benedek G., Farías D., Miranda, Rodolfo, Anemone G., Casado Aguilar P., Garnica, Manuela, Calleja, Fabián, Al Taleb A., Kuo C.-N., Lue C.S., Politano A., Vázquez de Parga, Amadeo L., Benedek G., Farías D., and Miranda, Rodolfo

Published
2021

22. Thermally Activated Processes for Ferromagnet Intercalation in Graphene-Heavy Metal Interfaces

Author

Ajejas F., Anadon A., Gudin A., Diez J.M., Ayani C.G., Olleros-Rodríguez P., De Melo Costa L., Navío C., Gutierrez A., Calleja, Fabián, Vázquez de Parga, Amadeo L., Miranda, Rodolfo, Camarero, Julio, Perna, Paolo, Ajejas F., Anadon A., Gudin A., Diez J.M., Ayani C.G., Olleros-Rodríguez P., De Melo Costa L., Navío C., Gutierrez A., Calleja, Fabián, Vázquez de Parga, Amadeo L., Miranda, Rodolfo, Camarero, Julio, and Perna, Paolo

Published
2020

23. Thermally Activated Processes for Ferromagnet Intercalation in Graphene-Heavy Metal Interfaces

Author

Ajejas F., Anadón A., Gudin A., Diez J.M., Ayani C.G., Olleros P., de Melo Costa L., Navío C., Gutierrez A., Calleja, Fabián, Vázquez de Parga, Amadeo L., Miranda, Rodolfo, Camarero, Julio, Perna, Paolo, Ajejas F., Anadón A., Gudin A., Diez J.M., Ayani C.G., Olleros P., de Melo Costa L., Navío C., Gutierrez A., Calleja, Fabián, Vázquez de Parga, Amadeo L., Miranda, Rodolfo, Camarero, Julio, and Perna, Paolo

Published
2019

24. Robust, carbon related, superconducting nanostructure at the apex of a tungsten STM tip

Author

Ayani C.G., Calleja, Fabián, Casado Aguilar P., Norris A., Navarro J.J., Garnica, Manuela, Acebrón M., Granados, Daniel, Vázquez de Parga, Amadeo L., Rodrigo J.G., Miranda, Rodolfo, Ayani C.G., Calleja, Fabián, Casado Aguilar P., Norris A., Navarro J.J., Garnica, Manuela, Acebrón M., Granados, Daniel, Vázquez de Parga, Amadeo L., Rodrigo J.G., and Miranda, Rodolfo

Published
2019

25. Electronic Properties of Sulfur Covered Ru(0001) Surfaces

Author

Pisarra, M., Diaz, Cristina, Bernardo Gavito, Ramon, Navarro, Juan Jesús, Black, Andrés, Calleja, Fabián, Granados, Daniel, Miranda, Rodolfo, Vázquez De Parga, Amadeo L., Martin, Fernando, Pisarra, M., Diaz, Cristina, Bernardo Gavito, Ramon, Navarro, Juan Jesús, Black, Andrés, Calleja, Fabián, Granados, Daniel, Miranda, Rodolfo, Vázquez De Parga, Amadeo L., and Martin, Fernando

Abstract

The structural properties of sulfur superstructures adsorbed on Ru(0001) have been widely studied in the past. However, much less effort has been devoted to determine their electronic properties. To understand the connection between structural and elec- tronic properties, we have carried out density functional theory periodic boundary calculations mimicking the four long range ordered sulfur superstructures identified experimentally by means of scanning tunneling microscopy (STM) techniques. Our simulations allow us to characterize the nature of the sulfur-Ru bond, the charge trans- fer between the Ru substrate and the sulfur adlayers, the interface states, as well as a parabolic state recently identified in STM experiments. A simple analysis, based on a one-dimensional model, reveals that this parabolic state is related to a potential well state, formed in the surface when the concentration of sulfur atoms is large enough to generate a new minimum in the surface potential.

Published
2018

27. Graphene catalyzes the reversible formation of a C–C bond between two molecules

Author

Navarro J.J., Pisarra M., Nieto-Ortega B., Villalva J., Ayani C.G., Díaz C., Calleja, Fabián, Miranda, Rodolfo, Martín, Fernando, Pérez, Emilio M., Vázquez de Parga, Amadeo L., Navarro J.J., Pisarra M., Nieto-Ortega B., Villalva J., Ayani C.G., Díaz C., Calleja, Fabián, Miranda, Rodolfo, Martín, Fernando, Pérez, Emilio M., and Vázquez de Parga, Amadeo L.

Published
2018

28. Evidence of large spin-orbit coupling effects in quasi-free-standing graphene on Pb/Ir(1 1 1)

Author

Otrokov M.M., Klimovskikh I.I., Calleja, Fabián, Shikin A.M., Vilkov O., Rybkin A.G., Estyunin D., Muff S., Dil J.H., Vázquez de Parga, Amadeo L., Miranda, Rodolfo, Ochoa H., Guinea, Francisco, Cerdá J.I., Chulkov E.V., Arnau A., Otrokov M.M., Klimovskikh I.I., Calleja, Fabián, Shikin A.M., Vilkov O., Rybkin A.G., Estyunin D., Muff S., Dil J.H., Vázquez de Parga, Amadeo L., Miranda, Rodolfo, Ochoa H., Guinea, Francisco, Cerdá J.I., Chulkov E.V., and Arnau A.

Published
2018

29. Electronic Properties of Sulfur Covered Ru(0001) Surfaces

Author

Pisarra M., Díaz C., Bernardo, Ramón, Navarro J.J., Black A., Calleja, Fabián, Granados, Daniel, Miranda, Rodolfo, Vázquez de Parga, Amadeo L., Martín, Fernando, Pisarra M., Díaz C., Bernardo, Ramón, Navarro J.J., Black A., Calleja, Fabián, Granados, Daniel, Miranda, Rodolfo, Vázquez de Parga, Amadeo L., and Martín, Fernando

Published
2018

30. Coverage evolution of the unoccupied Density of States in sulfur superstructures on Ru(0001)

Author

Pisarra M., Bernardo, Ramón, Navarro J.J., Black A., Díaz C., Calleja, Fabián, Granados, Daniel, Miranda, Rodolfo, Martín, Fernando, Vázquez de Parga, Amadeo L., Pisarra M., Bernardo, Ramón, Navarro J.J., Black A., Díaz C., Calleja, Fabián, Granados, Daniel, Miranda, Rodolfo, Martín, Fernando, and Vázquez de Parga, Amadeo L.

Published
2018

31. Evidence of large spin-orbit coupling effects in quasi-free-standing graphene on Pb/Ir(111)

Author

Eusko Jaurlaritza, Universidad del País Vasco, Ministerio de Economía y Competitividad (España), Tomsk State University, Comunidad de Madrid, Saint Petersburg State University, Russian Foundation for Basic Research, Russian Science Foundation, Otrokov, M. M., Klimovskikh, Ilya I., Calleja, Fabián, Shikin, Alexander M., Vilkov, Oleg Yu., Rybkin, Artem G., Estyunin, D., Muff, Stefan, Dil, J. Hugo, Vázquez de Parga, A. L., Miranda, Rodolfo, Ochoa, Héctor, Guinea, F., Cerdá, Jorge I., Chulkov, Eugene V., Arnau, Andrés, Eusko Jaurlaritza, Universidad del País Vasco, Ministerio de Economía y Competitividad (España), Tomsk State University, Comunidad de Madrid, Saint Petersburg State University, Russian Foundation for Basic Research, Russian Science Foundation, Otrokov, M. M., Klimovskikh, Ilya I., Calleja, Fabián, Shikin, Alexander M., Vilkov, Oleg Yu., Rybkin, Artem G., Estyunin, D., Muff, Stefan, Dil, J. Hugo, Vázquez de Parga, A. L., Miranda, Rodolfo, Ochoa, Héctor, Guinea, F., Cerdá, Jorge I., Chulkov, Eugene V., and Arnau, Andrés

Abstract

A combined scanning tunneling microscopy, angle- and spin-resolved photoemission spectroscopy and density functional theory study of graphene on Ir(1 1 1) intercalated with a well-ordered, full Pb monolayer is presented. Lead intercalation between graphene and Ir(111) reduces the coupling to the metallic substrate in such a way that its corrugation becomes negligible and distortions of the linear dispersion largely disappear, while graphene's sublattice symmetry is maintained and it turns out to be n-doped. Remarkably, the spin–orbit splittings induced by the proximity of the Ir(1 1 1) surface are preserved after Pb intercalation in a wide energy range. We further show that the Pb/Ir(1 1 1) surface induces a complex spin texture with both in-plane and out-of-plane components. Our calculations reveal the origin of the out-of-plane spin components in graphene to trace back to the out-of-plane spin-polarized surface and resonance states of Ir(1 1 1), while the Pb interlayer on its own does not induce any vertical spin polarization in the carbon sheet. However, the Brillouin zone folding imposed by the rectangular symmetry of the intercalated Pb layer plays an instrumental role in the spin–orbit coupling (SOC) transfer to graphene, as well as in the linearization of its bands. Finally, since no sizeable gap is observed at the Dirac point, we suggest that an intrinsic (Kane and Mele type) SOC does not exceed the extrinsic (Rashba) SOC for graphene on Pb/Ir(111).

Published
2018

32. Tuning Intermolecular Charge Transfer in Donor-Acceptor Two-Dimensional Crystals on Metal Surfaces

Author

Rodríguez-Fernández J., Robledo M., Lauwaet K., Martín-Jiménez A., Cirera B., Calleja, Fabián, Díaz-Tendero S., Alcamí M., Floreano L., Domínguez-Rivera M., Vázquez de Parga, Amadeo L., Écija, David, Gallego J.M., Miranda, Rodolfo, Martín, Fernando, Otero, Roberto, Rodríguez-Fernández J., Robledo M., Lauwaet K., Martín-Jiménez A., Cirera B., Calleja, Fabián, Díaz-Tendero S., Alcamí M., Floreano L., Domínguez-Rivera M., Vázquez de Parga, Amadeo L., Écija, David, Gallego J.M., Miranda, Rodolfo, Martín, Fernando, and Otero, Roberto

Published
2017

34. Tuning intermolecular charge transfer in donor-acceptor two-dimensional crystals on metal surfaces

Author

Ministerio de Economía y Competitividad (España), Comunidad de Madrid, Universidad Autónoma de Madrid, Ministero dell'Istruzione, dell'Università e della Ricerca, Ministerio de Ciencia e Innovación (España), Rodríguez-Fernández, Jonathan, Robledo, Maitreyi, Lauwaet, Koen, Martín-Jiménez, Alberto, Cirera, Borja, Calleja, Fabián, Díaz-Tendero, Sergio, Alcamí, Manuel, Floreano, Luca, Domínguez-Rivera, Marcos, Vázquez de Parga, Amadeo L., Écija, David, Gallego, José M., Miranda, Rodolfo, Martín, Fernando, Otero, Roberto, Ministerio de Economía y Competitividad (España), Comunidad de Madrid, Universidad Autónoma de Madrid, Ministero dell'Istruzione, dell'Università e della Ricerca, Ministerio de Ciencia e Innovación (España), Rodríguez-Fernández, Jonathan, Robledo, Maitreyi, Lauwaet, Koen, Martín-Jiménez, Alberto, Cirera, Borja, Calleja, Fabián, Díaz-Tendero, Sergio, Alcamí, Manuel, Floreano, Luca, Domínguez-Rivera, Marcos, Vázquez de Parga, Amadeo L., Écija, David, Gallego, José M., Miranda, Rodolfo, Martín, Fernando, and Otero, Roberto

Abstract

Organic charge transfer (CT) compounds display a wide range of exotic electronic properties (charge-density wave stabilization, Peierls transitions, etc.) depending on the amount of charge transferred from the donor (D) to the acceptor (A) species. A complete exploration of the complex electronic phase diagrams for such compounds would thus require methods to systematically tune the amount of charge exchanged in the CT process. This has proven however challenging in the past: chemical functionalization of the constituent molecules can also affect the packing of the molecular units in the crystal, whereas changing D:A stoichiometry is often not possible in the bulk. Interestingly, it was recently found that multiple stoichiometries can actually be achieved by codeposition of different amounts of D and A molecules on metal surfaces. The question, however, of whether CT processes between D and A molecules can be tuned with the D:A ratio in such mixtures has not yet been studied, and it is no trivial matter, since competing CT processes between the metal surface and the organic adsorbates might hinder interadsorbate charge transfer. Here we demonstrate that the CT process from the organic donor tetrathiafulvalene (TTF) to the acceptor tetracyanoquino-p-dimethane (TCNQ) can be tuned with exquisite accuracy (∼0.1 e) by controlling the stoichiometry of D:A cocrystals deposited on Ag(111). This control opens new avenues to explore the complex phase diagrams of organic CT compounds and to tailor their electronic properties.

Published
2017

35. Spatial variation of a giant spin-orbit effect induces Landau-like levels in graphene

Author

Calleja, Fabián, Ochoa, Héctor, Garnica, Manuela, Barja, Sara, Otrokov, M. M., Chulkov, Eugene V., Arnau, Andrés, Vázquez de Parga, A. L., Guinea, F., and Miranda, Rodolfo

Subjects
Physics::Atomic and Molecular Clusters
Abstract

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 large spin coherence length of electrons in graphene is an interesting characteristic in the potential development of spintronic devices. However, it could be exploited only if suitable spin manipulation techniques are found for graphene. A possible mechanism is the enhancement of the weak spin-orbit (S-O) coupling present in carbon atoms, for instance through the interaction with heavy metal atoms. Our experiments and calculations suggest that the partial intercalation of lead atoms in between a graphene sheet and an underlying iridium crystal leads to a spatial modulation of the S-O coupling that generates a pseudo magnetic field able to produce Landau-like levels in the density of states of graphene.

Published
2016

36. Tuning Intermolecular Charge Transfer in Donor–Acceptor Two-Dimensional Crystals on Metal Surfaces

Author

Rodríguez-Fernández, Jonathan, primary, Robledo, Maitreyi, additional, Lauwaet, Koen, additional, Martín-Jiménez, Alberto, additional, Cirera, Borja, additional, Calleja, Fabián, additional, Díaz-Tendero, Sergio, additional, Alcamí, Manuel, additional, Floreano, Luca, additional, Domínguez-Rivera, Marcos, additional, Vázquez de Parga, Amadeo L., additional, Écija, David, additional, Gallego, José M., additional, Miranda, Rodolfo, additional, Martín, Fernando, additional, and Otero, Roberto, additional

Published
2017
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38. Organic covalent patterning of nanostructured graphene with selectivity at the atomic level

Author

Navarro, Juan Jesús, Leret, Sofía, Calleja, Fabián, Stradi, Daniele, Black, Andrés, Bernardo-Gavito, Ramón, Garnica, Manuela, Granados, Daniel, Vázquez De Parga, Amadeo L., Pérez, Emilio M., Miranda, Rodolfo, Navarro, Juan Jesús, Leret, Sofía, Calleja, Fabián, Stradi, Daniele, Black, Andrés, Bernardo-Gavito, Ramón, Garnica, Manuela, Granados, Daniel, Vázquez De Parga, Amadeo L., Pérez, Emilio M., and Miranda, Rodolfo

Abstract

Organic covalent functionalization of graphene with long-range periodicity is highly desirable-it is anticipated to provide control over its electronic, optical, or magnetic properties-and remarkably challenging. In this work we describe a method for the covalent modification of graphene with strict spatial periodicity at the nanometer scale. The periodic landscape is provided by a single monolayer of graphene grown on Ru(0001) that presents a moiré pattern due to the mismatch between the carbon and ruthenium hexagonal lattices. The moiré contains periodically arranged areas where the graphene-ruthenium interaction is enhanced and shows higher chemical reactivity. This phenomenon is demonstrated by the attachment of cyanomethyl radicals (CH2CN•) produced by homolytic breaking of acetonitrile (CH3CN), which is shown to present a nearly complete selectivity (>98%) binding covalently to graphene on specific atomic sites. This method can be extended to other organic nitriles, paving the way for the attachment of functional molecules.

Published
2016

39. Organic Covalent Patterning of Nanostructured Graphene with Selectivity at the Atomic Level

Author

Navarro J.J., Leret S., Calleja, Fabián, Stradi D., Black A., Bernardo, Ramón, Garnica, Manuela, Granados, Daniel, Vázquez de Parga, Amadeo L., Pérez, Emilio M., Miranda, Rodolfo, Navarro J.J., Leret S., Calleja, Fabián, Stradi D., Black A., Bernardo, Ramón, Garnica, Manuela, Granados, Daniel, Vázquez de Parga, Amadeo L., Pérez, Emilio M., and Miranda, Rodolfo

Published
2016

41. Intercalation of sulfur in graphene/Ru(0001)

Author

Bernardo Gavito, Ramon, Black, Andrés, Navarro, Juan Jesús, Calleja, Fabián, Vázquez De Parga, Amadeo L., Granados, Daniel, Miranda, Rodolfo, Bernardo Gavito, Ramon, Black, Andrés, Navarro, Juan Jesús, Calleja, Fabián, Vázquez De Parga, Amadeo L., Granados, Daniel, and Miranda, Rodolfo

Published
2015

42. Covalent patterning of graphene with periodicity at the nanometer scale

Author

Navarro, Juan Jesús, Calleja, Fabián, Leret, Sofía, Stradi, Daniele, Black, Andrés, Bernardo Gavito, Ramon, Garnica, Manuela, Granados, Daniel, Vázquez De Parga, Amadeo L., Pérez, Emilio M., Miranda, Rodolfo, Navarro, Juan Jesús, Calleja, Fabián, Leret, Sofía, Stradi, Daniele, Black, Andrés, Bernardo Gavito, Ramon, Garnica, Manuela, Granados, Daniel, Vázquez De Parga, Amadeo L., Pérez, Emilio M., and Miranda, Rodolfo

Published
2015

43. Spatial variation of a giant spin-orbit effect induces electron confinement in graphene on Pb islands

Author

Calleja, Fabián, Ochoa H., Garnica, Manuela, Barja S., Navarro J.J., Black A., Otrokov M.M., Chulkov E.V., Arnau A., Vázquez de Parga, Amadeo L., Guinea, Francisco, Miranda, Rodolfo, Calleja, Fabián, Ochoa H., Garnica, Manuela, Barja S., Navarro J.J., Black A., Otrokov M.M., Chulkov E.V., Arnau A., Vázquez de Parga, Amadeo L., Guinea, Francisco, and Miranda, Rodolfo

Published
2015

44. Controlling the spin of Co atoms on Pt(111) by hydrogen adsorption

Author

Dubout Q., Donati F., Wäckerlin C., Calleja, Fabián, Etzkorn M., Lehnert A., Claude L., Gambardella P., Brune H., Dubout Q., Donati F., Wäckerlin C., Calleja, Fabián, Etzkorn M., Lehnert A., Claude L., Gambardella P., and Brune H.

Published
2015

45. Spatial variation of a giant spin-orbit effect induces electron confinement in graphene on Pb islands

Author

European Commission, European Research Council, Universidad del País Vasco, Eusko Jaurlaritza, Ministerio de Economía y Competitividad (España), Consejo Superior de Investigaciones Científicas (España), Calleja, Fabián, Ochoa, Héctor, Garnica, Manuela, Barja, Sara, Otrokov, M. M., Chulkov, Eugene V., Arnau, Andrés, Vázquez de Parga, A. L., Guinea, F., Miranda, Rodolfo, European Commission, European Research Council, Universidad del País Vasco, Eusko Jaurlaritza, Ministerio de Economía y Competitividad (España), Consejo Superior de Investigaciones Científicas (España), Calleja, Fabián, Ochoa, Héctor, Garnica, Manuela, Barja, Sara, Otrokov, M. M., Chulkov, Eugene V., Arnau, Andrés, Vázquez de Parga, A. L., Guinea, F., and Miranda, Rodolfo

Abstract

The electronic band structure of a material can acquire interesting topological properties in the presence of a magnetic field or as a result of the spin-orbit coupling. We study graphene on Ir, with Pb monolayer islands intercalated between the graphene sheet and the Ir surface. Although the graphene layer is structurally unaffected by the presence of the Pb islands, its electronic properties change markedly, with regularly spaced resonances appearing. We interpret these resonances as the effect of a strong and spatially modulated spin-orbit coupling, induced in graphene by the Pb monolayer. As well as confined electronic states, the electronic spectrum has a series of gaps with non-trivial topological properties, resembling a realization of the quantum spin Hall effect proposed by Bernevig and Zhang.

Published
2015

49. Probing the site-dependent kondo response of nanostructured graphene with organic molecules

Author

Comunidad de Madrid, Ministerio de Educación y Ciencia (España), Garnica, Manuela, Stradi, D., Calleja, Fabián, Barja, Sara, Díaz, Cristina, Alcamí, Manuel, Arnau, Andrés, Vázquez de Parga, A. L., Martín, Fernando, Miranda, Rodolfo, Comunidad de Madrid, Ministerio de Educación y Ciencia (España), Garnica, Manuela, Stradi, D., Calleja, Fabián, Barja, Sara, Díaz, Cristina, Alcamí, Manuel, Arnau, Andrés, Vázquez de Parga, A. L., Martín, Fernando, and Miranda, Rodolfo

Abstract

TCNQ molecules are used as a sensitive probe for the Kondo response of the electron gas of a nanostructured graphene grown on Ru(0001) presenting a moiré pattern. All adsorbed molecules acquired an extra electron by charge transfer from the substrate, but only those adsorbed in the FCC-Top areas of the moiré show magnetic moment and Kondo resonance in the STS spectra. DFT calculations trace back this behavior to the existence of a surface resonance in the low areas of the graphene moiré, whose density distribution strongly depends on the stacking sequence of the moiré area and effectively quenches the magnetic moment for HCP-Top sites. © 2014 American Chemical Society.

Published
2014

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