Research

Vision

I am a condensed matter theorist fascinated with the electronic and spin properties of quantum systems engineered with atomic scale precision.   The main motivation has been to explore quantum mechanics at the atomic scale, with the hope to make sense of the beautiful weirdness of the theory.   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. 

In the last 10 years I have focused my research in two main areas: 1) the electronic properties of graphene and other atomically thin  materials;  2) the exploration of individual atomic and nuclear  spins using STM.   A new focus of my research is to explore new strategies for Quantum Simulation, exploiting the resources provided by atomic scale manipulation.

Electronic properties  of 2D materials 

Scheme of a Van der Waals Spin Valve
(from C. Cardoso, D. Soriano,N. A. García
 and J. Fernández-Rossier,

Phys. Rev. Lett. 121, 067701 ('18))

The discovery of graphene, in 2004, started  a revolution  in Condensed Matter Physics,  providing a platform to study Dirac electrons. It was also a revolution in Material science,  starting the research in a new class of structures, 2D Crystals. 

In the incoming years, many other 2D crystals have been discovered,  with very different electronic properties: semiconductors, insulators, superconductors, and more recently ferromagnets, such as CrI3.  Things get even more interesting because it is relatively straight-forward to combine these materials to produce the so called Van der Waals heterostructures, with potential to create Quantum Composites,  quantum materials with electronic properties á la carte. In the figure I show such a device, a graphene bilayer whose conductivity is turned on and off depending on the relative magnetization of two adjacent layers of Cri3. 

Another fascinating recent development comes from the fabrication of graphene nanoribbons and nanoislands with atomically sharp edges.   In case of zigzag edges,  graphene  is expected to host a new type of  magnetic moment that, unlike atomic magnetism in normal ferromagnets,  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, including quantum bits and quantum simulators. 

Engineering quantum magnetism at the atomic scale 

Figure made by José Luis Lado.

A large part of my research is devoted to explore non-trivial spin physics in  engineered  atomic scale  structures that are fabricated, probed and manipulated with Scanning Tunneling Microscope (STM). 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 with a recently invented technique, electron spin resonance driven with STM-ERS.  In addition, the  magnetization of these engineered atomic scale nanomagnets can be  measured and manipulated by means of spin polarized STM.

The advances in atomic scale design of magnetic quantum structures, and the tremendous step forward in spin spectroscopy provided by ESR-STM,  make it now possible to use these artificial structures to carry out quantum simulations of  short-range spin model Hamiltonians, and to explore spin liquids,   spinons,   topologically protected fractional edge states, etc.