22nd CEMS Colloquium


Prof. Henrik Rønnow (Associate Professor, Laboratory for Quantum Magnetism, EPFL)


17:30 - 18:30, November 19, 2014 (Wednesday)


Okochi-Hall, RIKEN


Quantum Magnetism – neutrons in the quasi-particle zoo


The field of quantum magnetism forms an arena where theoretical models and experiments on real materials meet to further our understanding of quantum many body physics. I will illustrate the unique role of neutron scattering through results on selected Cu2+ based materials serving as physical realizations of fundamental low-dimensional spin 1/2 models. Balancing the borderline between classical antiferromagnetic order and quantum fluctuating ground states, in some ways, theoretical description of fully quantum ground states as found in spin chains and ladders is currently more advanced than for ordered spin clusters, or even the simple 2D square lattice. The antiferromagnetically ordered unfrustrated 2D square lattice hosts behaviour not explainable by spin-wave theory. This observation from inelastic neutron scattering may provide the ‘smoking gun’ of so-called resonating valence bonds (RVB) that Anderson and co-workers propose to describe the enigmatic high-Tc cuprate superconductors. Finally I will show how magnetic excitations can now also be investigated with high-resolution Resonant Inelastic X-ray Scattering (RIXS).