Please activate JavaScript!
Please install Adobe Flash Player, click here for download

Broschüre EMFL English

7 Dr Kamran Behnia Laboratoire de Physique et d’Étude des Matériaux, Paris »Over the past couple of decades, I’ve been exploring the way en- tropy is carried by electrons travelling in a solid body. One particu- larly interesting phenomenon is the  Nernst effect   , a tiny voltage, which appears when heat flows in the presence of a magnetic field. The Nernst effect is particularly significant in such semi-metals as bismuth and graphite, which have a low concentration of conduc- tion electrons. In these solids, a single mobile electron is shared by several thousand atoms, which gives it a rather long wavelength. Moreover, each single one of these electrons is extremely mobile and capable of carrying a lot of entropy. My group has become a regular visitor at the EMFL high field facil- ities where we are able to study the Nernst effect. For our investi- gations, we need strong magnetic fields. A magnetic field confines electrons to quantized orbits. The larger the magnetic field, the smaller the quantized orbit. A particularly interesting situation arises when the orbit’s radius becomes comparable to the electron wavelength. This is the quantum limit when the electron’s particle- and wave-like personalities clash. Our Nernst experiments have shown that the physics become highly complex in this case – much like an intricate puzzle with many different pieces that have to all be arranged in the proper order. Over the last few years, we have performed experiments on vari- ous systems ranging from superconductors to insulators in world- class facilities at Grenoble, Toulouse, and Nijmegen. Not only did our hosts at these facilities grant us access to their powerful magnets, they also shared with us their impressive technical know-how. We greatly appreciate the user-friendly atmosphere, which is very welcoming to people like us wishing to implement a new, unusual experimental technique in strong magnetic fields. We hope to be regular visitors at the EMFL facilities also in the future.« Why are magnetic fields so useful for research? Anyone who has ever played with a magnet will have witnessed its ability to attract iron from a distance. Magnetic fields force materials to change the orbit and magnetic spin of their elec- trons. This allows for changing and controlling of material prop- erties, with many benefits for applications and research. The tailored manipulation of material properties make high magnetic fields a perfect research tool. Today, strong magnets are used almost routinely in medical diagnostic equipment like MRI scanners, which expose patients to magnetic fields 50,000 times more powerful than Earth’s own magnetic field.