Quantum Magnetism and Superconductivity

The spin of the neutron allows neutron scattering to reveal the magnetic structure and dynamics of materials over nanometre length scales and picosecond timescales. Neutron scattering is particularly in demand in order to understand high-temperature superconductors, which lie close to magnetically ordered phases, and highly correlated metals with giant effective fermion masses, which lie close to magnetic order or pass through a mysterious phase of hidden order before becoming superconducting. Neutron scattering also is the probe of choice for revealing new phases of matter and new particles, as seen in the surprising behaviour of quantum spin chains and ladders where mass gaps and excited triplons replace conventional spin waves. Examples are given of quantum phenomena where neutron scattering has played a defining role that challenges current understanding of condensed matter.