Emergence of novel particles in quantum magnets

In condensed matter systems, novel particles may emerge at low temperatures and carry quantum numbers different from those of elementary particles. A well established example is the fractionally charged particles in the fractional quantum Hall state. It has long been proposed that similar fractionalized particles may emerge in certain quantum spin systems called quantum spin liquids that do not magnetically order down to the lowest temperatures. A particle called “spinon” which carries spin 1/2 like an electron but no charge, and its associated gauge field have long been sought after. After reviewing the basic concepts, I shall discuss the current status of this quest in several materials. A particularly promising example is a new kagome insulator with antiferromagnetic coupling. When subject to a strong magnetic field, it exhibits magnetization oscillations reminiscent of quantum oscillations in metals. This is a highly unusual phenomenon for an insulator and defies conventional explanations but has a natural interpretation in terms of emergent spinons and gauge fields.

Speaker: Patrick Lee, Massachusetts Institute of Technology