Radu Coldea Elected a Fellow of the American Physical Society

Congratulations to Professor Radu Coldea, the Walter Stern Fellow in Physics at Lincoln College, who has been elected a Fellow of the American Physical Society for his "significant contributions to the understanding of quantum magnetism and quantum phase transitions using neutron and resonant x-ray scattering”.

APS Fellowship is a prestigious recognition by one's professional peers to honour those who have made advances in physics through original research and publication, or made significant innovative contributions in the application of physics to science and technology. Each year, fewer than one half of one percent of the Society’s membership (excluding student members) is recognised by their peers for election to the status of Fellow of the American Physical Society.

About Radu's research

Radu’s research aims to understand the quantum rules that govern the behaviour of electrons in so-called quantum materials. Here strong interactions between electrons lead to them becoming strongly correlated (entangled) with one another, such that all electrons act together “in unison”, resulting in new, emergent properties of the system as a whole that cannot be understood in terms of properties of single electrons, i. e. the total is (much) more than the sum of the parts. Understanding under what circumstances such global quantum electronic states emerge - and what the organising principles are - is important from a fundamental physics point of view, but also has the potential to lead to the development of new types of quantum-based technologies.

Each electron has a “spin”, which is an intrinsic quantum property that can be loosely visualised as the electron spinning around its axis in a clockwise or anti-clockwise sense. In so-called quantum magnets, the electrons’ spins are strongly correlated with one another due to quantum effects associated with magnetic interactions. Radu’s research is specifically focused on exploring experimentally emergent phenomena in such materials using neutron beams to observe directly how the electron spins are arranged and how they fluctuate collectively, simultaneously using externally applied high magnetic fields to couple directly to the spins and to drive transitions between different collective quantum spin states.

To unravel the physics of quantum magnets, Radu works together with graduate students and postdoctoral researchers in his group, and collaborates also with scientists at other institutions in UK and worldwide, both experimentalists and theoreticians. Radu led research that discovered and explored in-depth experimentally several new forms of spontaneous magnetic order and cooperative dynamics in quantum magnets. This includes pioneering studies of the spin dynamics near quantum criticality in one of the theoretically most studied paradigms for a continuous quantum phase transition near absolute zero temperature - the Ising chain in a critical transverse magnetic field - revealing via inelastic neutron scattering how quasiparticles transform across the quantum critical point. The spectrum approached a universal structure near quantum criticality, as expected by conformal field theories predicting an emergent E8 spectrum. This was an important result as it was the first experimental evidence for the physical realisation in nature of this exceptional mathematical structure of quantum many-body states. Combining high magnetic fields and inelastic neutron scattering, Radu proposed and demonstrated a direct method to extract quantum spin Hamiltonians and quantum renormalisation factors experimentally, this general method has since been widely used by the experimental quantum magnetism community for research on quantum spin liquid candidate materials.

Radu has also made important contributions to the field of neutron scattering, by developing software tools for experiment simulation, data visualisation and quantitative analysis of multi-dimensional single-crystal time-of-flight inelastic neutron scattering that have been used by many research groups worldwide. The experimental results of Radu’s research have directly stimulated the development of new many-body quantum theories of frustrated quantum magnets, quantum spin liquids, fractionalisation and confinement in quasi-one-dimensional magnets, and dynamics at quantum phase transitions.