CM Seminar - Hidden magnetoelectric multipoles in multiferroics and superconductors

Most magnetic materials, phenomena and devices are well described in terms of magnetic dipoles of either spin or orbital origin. There is mounting evidence, however, that higher-than-dipolar order multipoles both exist (often in hiding) and lead to intriguing magnetic behaviors.  In this talk I will discuss the relevance of the so-called magnetoelectric multipoles, which form the next-order term, after the magnetic dipole, in the multipolar expansion of the magnetization density in a magnetic field.  First I will describe how magnetoelectric multipoles underlie multiferroic behavior and in particular how they determine the magnetic response to applied electric fields. Then I will discuss signatures of hidden magnetoelectric multipolar order, how it can be unearthed using density functional theory calculations and possibilities for its direct measurement.  Finally, I will suggest that such magnetoelectric hidden order occurs in the high-Tc cuprate materials, where it might be relevant for the superconducting behavior, providing a link between multiferroism and exotic superconductivity.

Nicola Spaldin is the Professor of Materials Theory at ETH Zurich. She is best known for her developement of the class of materials known as multiferroics, which combine simultaneous ferromagnetism and ferroelectricity. She is a passionate science educator, coordinator of the curriculum development project "The Materials Scientist 2030, Who is She?", and holder of the ETH Golden Owl Award for excellence in teaching. When not trying to make a room-temperature superconductor, she can be found playing her clarinet, or skiing or climbing in the Alps.