A quantum spin liquid is a hypothesized ground state of a
magnet without long-range magnetic order. Similar to a liquid, which is
spatially uniform and strongly correlated, a quantum spin liquid preserves all
the symmetries and exhibits strong correlations between spins. First proposed
by P. W. Anderson in 1973, it has remained a conjecture until recently. In the
past couple of years, numerical studies have provided strong evidences for
quantum spin liquid in a simple model, the kagome Heisenberg antiferromagnet. In this talk, I will describe a low-energy effective theory
for this magnet in terms of a lattice gauge theory with the simplest possible
mathematical structure (a group of two elements, namely Z2). I will show that
the theory reproduces many characteristic features observed numerically,
thereby providing a bridge between the numeircs and the analytics. Furthermore,
I will present theoretical predictions which could be tested in future
numerical studies.
