18 September 2020 Hugues Vincelette
Graduate portrait

Guillaume Hardy’s perseverance

Guillaume Hardy

Photo : IQ

More than 30 years after a ground-breaking discovery that won two IBM researchers, J. Georg Bednorz and K. Alexander Müller, a Nobel Prize in Physics in 1987, cuprates are still a subject of great interest in the world of physics. These high temperature (30o K) superconducting materials have great potential, especially for lossless transmission of electricity.

Guillaume Hardy, holder of a recent doctorate in physics, is also interested in this family of materials. After obtaining a diploma from the Sciences, lettres et arts program from the Cégep de Sherbrooke, Guillaume chose to undertake his bachelor’s degree in physics. The multiplicity of subjects to explore is what drew him to physics, whether it be astronomy, solid matter physics or fundamental physics.

Doctoral Project

Guillaume Hardy’s doctoral project is, in a way, the extension of his master’s work on doping by the proximity effect. It is as if superconductivity becomes contagious from one material to another, with the advantage of not having recourse to chemical substitution.

Guillaume follows a trail drawn by the work of Flavio Bruno and his collaborators. The team experimentally observed a transfer of electrons from one material to another, that is from Sm2CuO4 to LaFeO3, a parent compound. It would therefore be possible to dope the electron-doped cuprate by proximity.

At the master’s level, Guillaume had the opportunity to familiarize himself with the handling of samples, material fabrication by using the pulsed laser ablation technique, X-ray characterization, and transport measurements in a cryogenic system. These techniques have been of great help during his doctoral work.

He explains his doctoral project in a more detailed manner: “What interested us above all was resistivity and the Hall effect, from which we can determine the concentration of carriers. We used thin layers of varying thickness, in monolayers, bilayers, and superstructures, which are actually bilayers placed repeatedly. We could therefore determine the behaviour of the carriers near the interfaces between the layers. We finally realized that the task was more complex than we had anticipated, especially because of the high sensitivity of cuprates to the slightest variation in oxygenation. Indeed, Bruno’s team used sputtering, while we used pulsed laser ablation, which resulted in different oxygenations. In addition, to obtain quality layers, mesh disagreement must be minimized when different materials are deposited on top of each other. Therefore, a small difference between lattice parameters can vary the mobility of oxygen vacancies in materials. So, under certain growing conditions, we can see a behaviour appear which gives the impression that there is charge transfer.”

The Results

Guillaume’s results are surprising: “Despite our best efforts to obtain an electron transfer, we were unable to detect the slightest trace of this effect. We have tested it with different combinations of materials, and small variations in the methods of material growth can completely change the oxygenation conditions. This is what I demonstrated with my research,” explains Guillaume.

Obstacles to Overcome

Some obstacles strewed through Guillaume’s path during his doctorate. He gives us a sample: “In one project, the material used was extremely sensitive to even the slightest variation in growing conditions, making it difficult to precisely control the thickness of the layers.”

Prof. Patrick Fournier gives another perspective on these obstacles to underline Guillaume’s perseverance throughout his studies: “Guillaume showed great determination regarding the completion of his Ph.D. His project is in fact three projects integrated into one thesis requiring the use of complex and often defective instrumentation. In his case, he had to wait 8 months for the repair of a heating element designed for the heterostructures’ growth. But I think of something much more revealing about his determination, which is the moment when we realized that his initial study project of BaCuO2/SrCuO2 superstructures was compromised by an instability in its structures to the surrounding atmosphere. Literally, he could often watch his freshly prepared samples disappear before his eyes without being able to do anything about it! It worked, then it didn’t work… it could have discouraged him. Instead, however, he took advantage of the experience gained in this first project to quickly make progress, or rather attack the project finally presented in his thesis.”

The Next Steps

Guillaume does not have a defined plan in mind: he is contemplating the options available to him, in particular the possibility of carrying out a postdoctoral internship in order to have a university career. His motivation is his interest toward the study of solid materials. Thus, what remains is to determine where he can continue his research.

Good luck, Guillaume!


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