Eligible candidates must fulfill all the requirements necessary to apply for the PREDOC BERRI Fellowship program of the Department of Education of the Basque Government. Note that candidates must be currently resident in the Basque Country since at least 1 January 2018.
The PhD projects will be related to the current interests of the research groups at nanoGUNE:
- Nanomagnetism - Andreas Berger and Paolo Vavassori
- Nanooptics - Rainer Hillenbrand
- Self-Assembly - Alexander Bittner
- Nanobiomechanics - Raul Perez-Jimenez
- Nanodevices - Luis Hueso and Felix Casanova
- Electron Microscopy - Andrey Chuvilin
- Theory - Emilio Artacho
- Nanomaterials - Mato Knez
- Nanoimaging - Jose Ignacio Pascual
- Nanoengineering - Andreas Seifert
The PREDOC BERRI call of the Basque Government for 2018-2019 is now open and interested candidates are welcomed to submit their application together with their CV and Academic Record to the Group Leader of their interest no later than 15 June 2018.
All the information about the fellowships is available at these links:
The study has been publish in the journal Nature Communications and shows that it is possible to fabricate artificial materials, one by one, to produce electronic and magnetic properties that do not exist in any material found in nature. In this case, the scientists observed that conventional electrons in a metal becomes heavy electrons (the technical denomination is heavy fermions) in the proximity of ordered atomic structures of magnetic atoms (cobalt) arranged over the surface. Heavy fermions are electronic states that appear when normal electrons, which are intrinsically magnetic, are attracted towards the structure of magnetic atoms periodically arranged.
The researchers employed a Scanning Tunnelling Microscope at low temperatures to study the shape of this electronic states and demonstrate that they correspond to the emergence of a heavy fermion state. This is te first time that te formation of such novel state of matter is monitored by constructing the artificial material one atom at a time. “We found that the magnetic fingerprint of this electrons extended delocalized along a magnetic chain of up to 20 cobalt atoms, allowing us to demonstrate that they correspond to a new electronic state of matter, and provide a theoretical model for creation of heavy electrons that could be extended to other systems, thus boosting the search of artificial materials with novel functional properties.” Explains David Serrate, scientists in ICMA and leader of this study.
The exotic electronic and magnetic properties of this materials cause great expectations in their possible use for applications such a sensors, superconducting devices or to explore critical quantum proceses. Heavy electrons behave drastically different than normal electrons, because their response to temperature, pressure of magnetic fields scales with the mass of the electrons. Additionally, the observation of these novel states inspire new theoretical models that allows us to explore the quantum limits of matter and design new artificial materials with customized electronic behaviour.
An international committee including leading researchers in the field was selected to assess the research project:
- Dra. Isabel Guillamón (Universidad Autónoma de Madrid). http://www.uam.es/UAM/Home.htm?language=es
- Dr. Andrés Arnau (Universidad del País Vasco UPV/EHU).
- Dr. Jeans Wiebe (University of Hamburg).
After the defense, we asked Dr. Javier Zaldivar to explain us a bit more about his project:
Which was the subject of your thesis?
My work focuses on two topics: STM studies of Yu-Shiba-Rusinov (YSR) states emerging from isolated magnetic atoms deposited on the surface of a superconductor and how YSR states are modified when these atoms are combined to form chains. From a broader perspective, I would say in my thesis we studied the atomic-scale interaction of magnetism and superconductivity, and the possibility of engineering novel states of matter from that interaction.
Why did you choose this subject?
YSR states are a hot topic in the low-temperature STM and quantum computation communities. Few-nm-sized chains of magnetic atoms on the surface of superconductors hold the potential to host modes equivalent to Majorana fermions, a kind of particle with no equivalent outside the world of condensed matter. These modes are a necessary requirement for the development of some proposed platforms for topological quantum computation. We chose this subject because we wanted to understand how YSR states, already an unconventional type of state, can be tuned to resemble a Majorana fermion.
Which metodology/techniques did you use?
Our work is a set of purely STM-based experiments. Atoms are deposited on the surface of a superconductor inside an STM chamber under an extremely clean atmosphere and temperatures of approximately 1 kelvin. Using Scanning Tunneling Spectroscopy we identify the signatures of individual magnetic atoms and use the STM tip to push these atoms one by one to construct custom nano-sized structures containing ten to twenty atoms.
Theoretical predictions usually focus on how the magnetic interactions between atoms tune YSR states to yield Majorana modes. Although we studied the experimental signatures of such interactions and confirmed they hold in real experiments, I think our main conclusion is that the band structure of the superconducting material, an overlooked part of the problem in theoretical predictions, plays a fundamental role in the formation of Majorana modes.
What could be the contribution of your research for present or future nanotechnologies?
The work presented in my thesis focuses on the fundamental properties of assemblies of atoms, a field very distant from that of applied physics. The requirement of atomic-scale-control and very low temperatures prevents the use of our results in current-day technologies. Further research could automatize the construction of chains and the manipulation of Majorana modes, but several stages of research are still required to transform those ideas into a commercially-available technology.
How do you feel now that you have finished the thesis? Which are your plans for the future?
Having finished my thesis, I feel a sense of accomplishment and the satisfaction of giving my best over all this time. I have been surrounded by a team of excellent researchers, from whom I have learnt ideas that have expanded my knowledge of physics further more than I could have imagined when I first visited nanoGUNE some five years ago. Studying exotic phenomena at the atomic scale has been a very stimulating experience, however I am now focused on redirecting my career towards more applied topics.
The meeting marks the starting point of a 4-year research project that is coordinated by CIC nanoGUNE and integrates IBM Research, Donostia International Physics Center, and University of Santiago de Compostela, Technical University of Delft and the University of Oxford. The consortium of these 6 leading European research institutions has been granted a total of €3.5 million from the European Commission under the highly competitive Horizon 2020 FET-Open call, which funds cutting-edge high-risk / high-impact interdisciplinary research projects that must lay the foundations for radically new future technologies.
The SPRING project combines recent scientific breakthroughs from the consortium members to fabricate custom-crafted magnetic graphene nanostructures and test their potential as basic elements in quantum spintronic devices. The targeted long-term vision is the development of an all-graphene – environmentally friendly – platform where spins can be used for transporting, storing and processing information.
The spin is an intrinsic property of electrons that makes them behave like tiny magnets. For instance, every electron in any material carries both a charge and a spin, the latter playing a key role in magnetism.
Within the scientific community there is consensus that spin is the ideal property of matter to expand the performance of current charge-based nanoelectronics into a class of faster and more power-efficient components, being the basis for the emerging technology called quantum spintronics. The SPRING project will investigate the fundamental laws for creating and detecting spins in graphene, this is to read and write spins, and using them to transmit information.
Jose Ignacio Pascual, Ikerbasque Research Professor at CIC nanoGUNE and scientific coordinator of the project, explains that “graphene is ideal to host spins and to transport them. This atomically thin material can now be fabricated with atomic precision, opening the door to fabrication of designer structures with precise shape, composition, spin arrangement, and interconnected by graphene electrodes for electrostatic or quantum gates. The potential is a platform for the second quantum revolution as qubit elements for quantum computation.”
In a new study, published in Physical Review Letters , this challenge was revisited using a scanning tunneling microscope (STM). After assembling a triangular-like piece of graphene on a clean gold surface, high-resolution scanning tunneling spectroscopy measurements revealed that this compound has a net magnetic state characterized by a spin S=1 ground state and, therefore, that this molecule is a small, pure carbon paramagnet. These results are the first experimental demonstration of a high-spin graphene flake.
The findings were further complemented with atomic manipulation steps of hydrogen-passivated triangulene side-products occasionally found in the experiment. By controlled removal of these additional hydrogen atoms in the experiments, the spin state of the flake could be modified from a closed-shell, doubly hydrogenated structure, to an intermediate S=1/2 spin state, and finally to the high-spin S=1 state of the ideal molecular structure.
The experimental proof of a spin-state in the absence of a magnetic quantization axis (detectable by spin-polarized STM) or magnetic anisotropy (detectable by spin-flip inelastic tunneling spectroscopy) is not simple. In this work, the spin signature was obtained from the underscreened Kondo effect – an exotic version of the standard Kondo effect described in the 1960s – that can arise in high-spin systems. Its observation in a graphene flake on a metal has not been reported before and brings here novel insights to understanding spins interacting with surfaces.
The work was the result of a fruitful collaboration between theoretical and experimental groups at the Donostia International Physics Center (DIPC) and CIC nanoGUNE, both research institutes in San Sebastian, as well as an organic synthesis group at CiQUS, in Santiago de Compostela.