Research

Vision

I am a condensed matter theorist fascinated with the electronic and spin properties of quantum systems engineered with atomic scale precision. My motivation comes primarily from the curiosity to understand fundamental open questions of quantum mechanics and many body physics. As a bonus, this field of research holds the potential to provide solutions to the challenges faced by the electronics industry to keep moving on with the miniaturization of electronic devices and to create a new technological revolution based on quantum technologies. My work relies mostly on model Hamiltonians, occasionally on density functional theory (DFT) calculations, and very often in non-equilibrium quantum dynamics and quantum transport simulations. Most of my research in the last few years can be split in two main topics, dealing with atomic scale spintronics and graphene spintronics. 

Spintronics in Graphene and other 2 dimensional crystals

Spins in graphene. Image courtesy of J. W. González  


The electronic transport and optical  properties of graphene   are unique in many counts,  because the two quantities that control these properties in other materials, the gap energy and the density of states at the Fermi level,  vanish. The spin properties of graphene are also different.The formation of magnetic moments in magnetic materials is most often associated to the reduction of Coulomb repulsion for electrons occupying degenerate atomic levels  in open  d and f shells. This phenomenon is understood since the early days of quantum mechanics and accounts for our understanding of magnetic materials based on transition metals and rare earth.

In contrast, graphene  is expected to host  of a different kind of magnetic moment that occupies at least 3 atoms and is associated to degeneracies  at the molecular level.  These magnetic moments emerge at the zigzag edges of graphene as well as at vacancies and in the neighbourhood of chemisorbed atoms, such as hydrogen and fluorine.  One of the goals of my research it   to understand the emergence of local moments in graphene and how to detect them as well as how to use them in practical applications. 

 I am also interested in understanding  the influence of materials that are either ferromagnetic or have a strong spin orbit coupling, on the electronic properties of  graphene and other 2D crystals, such as MoS2.   Ongoing and future research includes also  the  study of  electronic and transport properties of the recently observed spin filtered edge states  in graphene Quantum Hall bars and    on the effect of spin orbit coupling on the  electronic structure and spin transport of  MoS2 (and related materials) as well as atomically thin Bi(111). 

My ongoing work in this area is very much related to the European Project SPINOGRAPH  on "Spintronics in Graphene", that I coordinate, and is participated by 8 more  groups including  those of Nobel Laureates Geim (Manchester) and  Fert (CNRS, Paris).

Atomic Scale Spintronics

Spintronics aims to take advantage of the spin degree of freedom for practical applications in solid state devices.  Remarkably, there is a variety of solid state systems in which  a single or a few magnetic atoms control the properties of the entire device and even  afford functionality for practical applications.
This is giving birth to the new research field of Atomic scale spintronics

Specific examples of this are    engineered  atomic scale  structures that are fabricated, probed and manipulated with Scanning Tunneling Microscope. This includes both individual magnetic atoms and arrangements of atoms forming  spin chains. Their spin excitations are probed with inelastic electron tunneling spectroscopy (IETS), and in some instances their magnetization is measured and manipulated by means of spin polarized STM magnetometry .

Understanding the  fundamental question of how the classical magnetism behavior emerges in this type of systems is one of my main goals. This is motivated in part by the  observations that show the crossover from quantum magnetism behavior for chains of less than 8 iron atoms to classical behavior, for larger systems.   

The exploration of  the  collective spin excitations  in quantum spin chains, such as spinons,  spin waves,  and topologically protected fractional edge states,  in these engineered finite size spin chains is another exciting venue.  Specifically, theory should address how these excitations can be probed, and what are the effects of finite size and coupling of the spin chain to the dissipative  environment provided by the conducting electrons of the STM tip and substrate.