Abstract: Magnetism, first encountered by humans thousands of years ago in naturally occurring lodestones, remains one of the most intriguing phenomena in physics. As physicists, we have learned that electricity and magnetism can be described by Maxwell’s equations. Yet the behavior of magnetism inside materials remains surprisingly difficult to understand. In the past 60 years, we have found that when some magnetic materials are cooled close to absolute zero, the rules of quantum mechanics can lead to behavior with no analogue in our everyday world.

One particularly interesting situation occurs when the magnetic atoms in a material cannot simultaneously satisfy all of their preferred interactions. This “magnetic frustration” can prevent the spins from settling into an ordered arrangement, allowing quantum fluctuations to dominate instead. In extreme cases, this can produce a quantum spin liquid: an unusual state of matter in which the magnetic moments remain dynamic even at temperatures approaching absolute zero and can give rise to entirely new collective phenomena.

In this talk, I will introduce how physicists design, synthesize, and study quantum magnetic materials, and how experiments using techniques such as neutron scattering allow us to peer inside of materials to see what their spins are doing at the atomic scale. I will discuss the decades-long search for quantum spin liquids, why identifying one experimentally has proven so difficult, and how the search continues to uncover unexpected physics in new materials.