J. Fernández‐Rossier

International Iberian Nanotechnology Laboratory

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José L. Lado

Aalto University

J. J. Palacios

Universidad Autónoma de Madrid

David Jacob

University of the Basque Country

F.S. Delgado

Universidad de La Laguna

Gonçalo Catarina

Swiss Federal Laboratories for Materials Science and Technology

Ricardo Ortiz

SUNY Korea

C. Tejedor

Universidad Autónoma de Madrid

Alejandro Ferrón

National University of the Northeast

A. T. Costa

International Iberian Nanotechnology Laboratory

J. C. G. Henriques

Universidade de Santiago de Compostela

Cooperative Institutions

Centre National de la Recherche Scientifique

University of Alicante

Universidad Autónoma de Madrid

International Iberian Nanotechnology Laboratory

Instituto de Ciencia de Materiales de Madrid

Consejo Superior de Investigaciones Científicas

Delft University of Technology

University of Minho

Institut Néel

Université Grenoble Alpes

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Report on 1703.05029v2

arXiv (Cornell University) (2017)

Ján Girovský José L. Lado Floris Kalff E Fahrenfort L Peters

The interaction of electrons with a periodic potential of atoms in crystalline solids gives rise to band structure.The band structure of existing materials can be measured by photoemission spectroscopy and accurately understood in terms of the tight-binding model, however not many experimental approaches exist that allow to tailor artificial crystal lattices using a bottom-up approach.The ability to engineer and study atomically crafted designer materials by scanning tunnelling microscopy and spectroscopy (STM/STS) helps to understand the emergence of material properties.Here, we use atom manipulation of individual vacancies in a chlorine monolayer on Cu(100) to construct one-and two-dimensional structures of various densities and sizes.Local STS measurements reveal the emergence of quasiparticle bands, evidenced by standing Bloch waves, with tuneable dispersion.The experimental data are understood in terms of a tight-binding model combined with an additional broadening term that allows an estimation of the coupling to the underlying substrate.

10.21468/scipost.report.124

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Landau levels in 2D materials using Wannier Hamiltonians obtained by first principles

2D Materials (2016)

José L. Lado J. Fernández‐Rossier

We present a method to calculate the Landau levels and the corresponding edge states of two dimensional (2D) crystals using as a starting point their electronic structure as obtained from standard density functional theory (DFT). The DFT Hamiltonian is represented in the basis of maximally localized Wannier functions. This defines a tight-binding Hamiltonian for the bulk that can be used to describe other structures, such as ribbons, provided that atomic scale details of the edges are ignored. The effect of the orbital magnetic field is described using the Peierls substitution in the hopping matrix elements. Implementing this approach in a ribbon geometry, we obtain both the Landau levels and the dispersive edge states for a series of 2D crystals, including graphene, Boron Nitride, MoS$_2$ , Black Phosphorous, Indium Selenide and MoO$_3$ . Our procedure can readily be used in any other 2D crystal, and provides an alternative to effective mass descriptions.

Wannier function

Hamiltonian (control theory)

Landau quantization

Ribbon

Crystal field theory

Tight binding

10.1088/2053-1583/3/3/035023

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Probing magnetism in 2D van der Waals crystalline insulators via electron tunneling

Science (2018)

Dahlia Klein David MacNeill José L. Lado David Soriano Efrén Navarro‐Moratalla

Magnetic insulators are a key resource for next-generation spintronic and topological devices. The family of layered metal halides promises ultrathin insulating multiferroics, spin liquids, and ferromagnets, but new characterization methods are required to unlock their potential. Here, we report tunneling through the layered magnetic insulator CrI3 as a function of temperature and applied magnetic field. We electrically detect the magnetic ground state and inter-layer coupling and observe a field-induced metamagnetic transition. The metamagnetic transition results in magnetoresistances of 95%, 300%, and 550% for bilayer, trilayer, and tetralayer CrI3 barriers, respectively. We further measure inelastic tunneling spectra for our junctions, unveiling a rich spectrum of collective magnetic excitations (magnons) in CrI3. Our results establish vertical tunneling as a versatile probe of magnetism in atomically thin insulators.

Magnetism

Magnon

10.1126/science.aar3617

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Strong magnetic proximity effect in Van der Waals heterostructures driven by direct hybridization

arXiv (Cornell University) (2023)

Cláudia Cardoso A. T. Costa A. H. MacDonald J. Fernández‐Rossier

We propose a new class of magnetic proximity effects based on the spin dependent hybridization between the electronic states at the Fermi energy in a non-magnetic conductor and the narrow spin split bands of a ferromagnetic insulator. Unlike conventional exchange proximity, we show this hybridization proximity effect has a very strong influence on the non-magnetic layer and can be further modulated by application of an electric field. We use DFT calculations to illustrate this effect in graphene placed next to a monolayer of CrI$_3$, a ferromagnetic insulator. We find strong hybridization of the graphene bands with the narrow conduction band of CrI$_3$ in one spin channel only. We show that our results are robust with respect to lattice mismatch and twist angle variations. Furthermore, we show that an out-of-plane electric field can be used to modulate the hybridization strength, paving the way for applications.

Fermi energy

Exchange interaction

10.48550/arxiv.2305.16813

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Landau Levels in two dimensional materials from first principles

arXiv (Cornell University) (2016)

José L. Lado J. Fernández‐Rossier

Landau quantization

Hamiltonian (control theory)

Ribbon

Wannier function

Crystal field theory

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Ultrafast Coherent Spectroscopy of the Fermi Edge Singularity

Springer eBooks (2007)

Diego Porras J. Fernández‐Rossier C. Tejedor

Bosonization

Formalism (music)

10.1007/3-540-45557-4_53

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Engineering spin exchange in nonbipartite graphene zigzag edges

Physical review. B./Physical review. B (2016)

Ricardo Ortiz José L. Lado Manuel Melle‐Franco J. Fernández‐Rossier

The rules that govern spin exchange interaction in pristine graphene nanostructures are constrained by the bipartite character of the lattice, so that the sign of the exchange is determined by whether magnetic moments are on the same sublattice or not. The synthesis of graphene ribbons with perfect zigzag edges and a fluoranthene group with a pentagon ring, a defect that breaks the bipartite nature of the honeycomb lattice, has been recently demonstrated. Here we address how the electronic and spin properties of these structures are modified by such defects, both for indirect exchange interactions as well as the emergent edge magnetism, studied both with density functional theory and mean-field Hubbard model calculations. In all instances we find that the local breakdown of the bipartite nature at the defect reverts the sign of the otherwise ferromagnetic correlations along the edge, introducing a locally antiferromagnetic intraedge coupling and, for narrow ribbons, also revert the antiferromagnetic interedge interactions that are normally found in pristine ribbons. Our findings show that these pentagon defects are a resource that permits us to engineer the spin exchange interactions in graphene-based nanostructures.

Zigzag

Magnetism

Lattice (music)

10.1103/physrevb.94.094414

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Premio Nobel de Física 2016: Revolución topológica en materia condensada

Revista española de física (2016)

Alberto Cortijo Elsa Prada Pablo San-José Ramón Aguado J. Fernández‐Rossier

La fisica de la materia condensada es mucho mas que una rama de la fisica: es una forma diferente de mirar al universo enraizada en el concepto de emergencia. E sta idea, propuesta por Philip W. Anderson en su famoso articulo de 1972 “More is different” [1] y desarrollada por Robert Laughlin [2], entre otros, defiende que el todo es mucho mas que la simple suma de las partes. Las propiedades de un sistema compuesto, ya sea un cristal, una proteina, o un nucleo atomico, no se pueden deducir, en la practica, de las propiedades de las piezas que los componen (atomos, aminoacidos, quarks), sino que emergen como consecuencia de la organizacion espontanea de sus constituyentes. Dichas propiedades nacen de la complejidad del conjunto y no pueden entreverse analizando los constituyentes por separado: una sinfonia de Beethoven se caracteriza por patrones que se pierden de vista al considerar las notas musicales por separado; saber tres acordes, haciendo referencia a otro premio Nobel de este ano, no te garantiza componer canciones como las de Bob Dylan.

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Long range spin qubit interaction mediated by microcavity polaritons

Bulletin of the American Physical Society (2007)

Carlo Piermarocchi G. F. Quinteiro J. Fernández‐Rossier

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Hyperfine interaction in hydrogenated graphene

Bulletin of the American Physical Society (2016)

N. García Manuel Melle J. Fernández‐Rossier

We study the hyperfine interaction of Hydrogen chemisorbed in graphene nanostructures with a gap in their spectrum, such as islands and ribbons. Chemisorption of Hydrogen on graphene results in a bound in-gap state that hosts a single electron localized mainly in the first neighbours around the adatom. Using both density functional theory and a four-orbital tight-binding model we study the hyperfine interaction between the hydrogen nuclear spin and the conduction electrons in graphene. We find that the strength of the hyperfine interaction decreases for larger nanostructures as the energy gap gets is smaller. We then compare the results of the hyperfine interaction for large nanostructures, obtaining very similar results. The magnitude of the hyperfine interaction is about 150 MHz, in line with that of Si:P. We acknowledge financial support by Marie-Curie-ITN 607904-SPINOGRAPH. References [1] D. Soriano, et al. Phys. Rev. B 81, 165409 (2010) [2] Rachpon Kalra, et al. Phys. Rev. X 4, 021044 (2014) [3] Juha T. Muhonen, et al. Nature Nanotechnology 9, 986–991 (2014)

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