Doctoral degree 'cum laude' for Maarten Berben
As part of the national research programme Strange Metals, funded by NWO, Maarten Berben investigated two families of low dimensional and superconducting materials with electronic transport measurements under the influence of magnetic fields. He discovered that these metals also show strange behaviour when it comes to magnetoresistance. This suggests a new paradigm for magnetotransport in strange metals. Based on the outstanding quality of the thesis and excellent defence the Doctoral Examination Board awarded him a doctorate with the distinction ‘cum laude’.
Maarten Berben started at HFML-FELIX during his Physics Master Internship. When a PhD position became available soon afterwards within the Strange Metals program, he didn’t hesitate. “I liked being in the laboratory and I have always been fond of digging in technical complex and difficult issues. And as the Strange Metal Program involves both experimental and theoretical groups in Nijmegen, Leiden, Amsterdam and Utrecht, I would be able to collaborate with several other research groups in the Netherlands. I actually started my PhD at the University of Amsterdam.”
Strange metals are called 'strange' because their behaviour deviates from the standard properties of metals. Maarten Berben performed multiple types of measurements on strange metals to get a clearer view on their behaviour. Most of the research has been carried out at HFML-FELIX and, to extend the magnetic field range, in the pulsed field facility LNCMI-T, Toulouse. “There was no way I could go to France during the pandemic, but it was essential for my research. Luckily, the staff in Toulouse was willing to perform our experiments remotely. These measurements were very successful and are an important part of my thesis.”
Eye-catching is his Nature publication with another PhD student in Hussey’s group, Jake Ayres. “Both of us found an unexpected behaviour in our measurements. By merging our datasets we could show that these strange metals don’t obey the standard rules of ordinary metals. The magnetoresistance behaves similar to what was previously seen near quantum critical points, but now in an extended range. Furthermore, these results imply that this magnetoresistance is caused by 'incoherent'carriers rather than by orbital motion.
Although the results presented in my thesis certainly shed some light on the behaviour of strange metals, much is still unknown. I hope my research motivates further experimental and theoretical studies into the strange and enigmatic behaviour of strange metals.”
Maarten Berben has started May 1st as a Physics Design Engineer at ASML.
The defence took place on Monday 23 May.
Promotor: prof. dr. N.E. Hussey