Quantum superalgebra slq(21) on the Poincaré half-plane

We find that the symmetry algebra for the motion of a spin-12 electron moving in the Poincaré upper half-plane (H) under the action of a constant magnetic field (orthogonal to H) is the quantum superalgebra slq(21). From this, and using representation theory, we are able to determine the degree of degeneracy of the lowest Landau level when q is a root of unity.