Spin Ice―A Prototype of Quantum Spin Liquid

Abstract

Spin ice draws continuing interest since its discovery in 1999, due to its outstanding character as a magnetic counterpart of water ice. The quantum version of spin ice, a quantum spin ice, gives a typical example of quantum spin liquid state, which is described by a gauge theory analogous to quantum electrodynamics. It is usually quite hard to describe the dynamics of strong-coupling gauge theory. However, recent theoretical progress enables a precise description of the fractional excitation, called magnetic monopole, which sheds light on the experimental identification of quantum spin liquid phase in spin ice materials.