Magnetism has commanded human wonder through millennia and it is a central component of the technologies that shape our lives. For the past 50 years scientists have been in pursuit of a radically new form of magnetism that would constitute a new state of matter: The quantum spin liquid may exist within a crystalline solid composed of atoms that carry a magnetic dipole moment. However, quantum fluctuations of these dipole moments preclude the development of conventional magnetic order even at temperature far below the scale of inter-site interactions. The result is a quantum material with unique macroscopic properties driven by quantum coherence and entanglement. If we can realize the materials physics of the quantum spin liquid these properties can be fully explored and might lead to interesting applications much as other advances we have made in our understanding of magnetism.
In the ongoing quest for a robust realization of a quantum spin liquid in the lab, a range of interesting magnetic materials and phenomena have been discovered. I shall review experiments probing interacting quantum spins on kagome, honeycomb, and triangular lattices in 2D and on the pyrochlore lattice in 3D. These frustrated quantum magnets feature an intermediate energy and temperature regime with spin-liquid-like properties but also unique low temperature phases driven by quenched disorder or lattice instabilities. Such inevitable deviations from ideal spin liquid models are interesting in their own right and their elucidation may contribute to understanding age old puzzles such as the phase diagram of V2O3 which I shall describe in greater detail in my seminar the following day.