The Department of Physics is delighted to welcome Professor Paolo Radaelli (University of Oxford) as a Colloquium Speaker for the academic year 2026/27. Please join us to listen to Professor Radaelli's seminar.
A reception will be held directly after the seminar, where tea and coffee will be provided.
The seminar is open to anyone from the university, students are encouraged to attend.
Title
Symmetry and driven matter
Abstract
Recent developments in lasers and optical sources, and specifically the ability to generate frequency-tuneable, large-amplitude pulses of controllable duration in the 10-30 THz regime, have allowed for experiments in which specific collective modes are addressed resonantly and can be coupled non-linearly to other modes – so-called non-linear phononics. In turn, these modes also couple with electronic degrees of freedom, so that pumping in the ultra-fast regime can induce properties (e.g. ferroelectricity, ferromagnetism or superconductivity) that are generally expected to appear on cooling through phase transitions. There is hope that this technique will eventually stabilise ‘phases of matter’ that do not occur in equilibrium. In the absence of a comprehensive theoretical interpretation and modelling of these experiments, symmetry considerations are of paramount importance and have been successfully used both to predict the ‘emergence’ of these properties [1] and to select specific linear/non-linear optical probes to identify them unambiguously. I will discuss examples from our recent work where symmetry played a key role in predicting the emergence of light-induced ferrimagnetism [2] structural chirality [3] and axiality [4] and helped to design the experimental protocols to detect them in the ultra-fast regime. Symmetry principles guiding ultra-fast experiments can also be applied ‘in reverse’ to (re)discover surprising effects that occur in equilibrium.
Bio
Paolo Radaelli is Dr Lee’s Professor of Experimental Philosophy at Oxford’s Clarendon Laboratory and a Professorial Fellow in Physics at Wadham College. His career has taken him from Milan and the Illinois Institute of Technology to Argonne National Laboratory, CNRS Grenoble, the Institut Laue–Langevin and the ISIS Neutron and Muon Source at Rutherford Appleton Laboratory.
He is a recipient of the Institute of Physics Occhialini Medal and has been made a Knight of the Order of the Star of Italy by the President of the Italian Republic.
Paolo’s research sits at the intersection of light, advanced materials and computation. A central question in his work is whether entirely new physical principles can be harnessed to create faster and dramatically more energy-efficient ways of computing.
One particularly intriguing direction involves “magnetic knots” — tiny, stable structures in the magnetic state of a material. Paolo and his collaborators demonstrated how such structures can be created in remarkably simple materials, including iron oxides closely related to rust. These magnetic structures offer a potential route towards new forms of information processing at microwave frequencies relevant to technologies such as 5G and 6G.
A second strand of his research explores what happens when materials are driven by precisely tuned pulses of light. The interaction can temporarily give a material properties that it does not possess under normal conditions, sometimes for only a few trillionths of a second. Understanding and ultimately controlling these fleeting states could open new approaches to photonics, information processing and energy-efficient computation.