Brookhaven Lecture

From electronic gadgets and functional materials to chemical reactions and biological systems, the world around us functions by virtue of electronic motions. The complex "dances" of electrons are governed by the laws of quantum mechanics, which dictate how electrons flow and how they form various quantum phases and functionalities, such as magnetism and superconductivity. These quantum phenomena underlie broad range of modern technologies in energy production, transportation, medicine, and computing. Because each electron carries a quantum of angular momentum, or spin, acting as a microscopic magnet attached to it, the quantum electronic arrangements have specific spin patterns. In a ferromagnet, electronic spins are parallel, and in a conventional superconductor, electrons form pairs with their spins anti-parallel. Neutron scattering presents a unique microscopic probe of electronic spin patterns in quantum materials. Being electrically neutral, a scattering neutron does not perturb delicate electronic phases, but illuminates quantum arrangements and motions of electronic magnetic moments. Brookhaven scientists played leading role in advancing neutron scattering research since its very inception. This lecture will describe recent progress in neutron scattering technology and discuss how it was used to understand relationships between magnetism and superconductivity in some unconventional superconductors.