Bilayer Quantum Hall Systems at Filling Factor $\nu =2\mathrm{}$: An Exact Diagonalization Study

We present an exact diagonalization study of bilayer quantum Hall systems at filling factor $\nu =2\mathrm{}$ in the spherical geometry. We find the high-Zeeman-coupling phase boundary of the broken symmetry canted antiferromagnet is given exactly by previous Hartree-Fock mean-field theories, but that the state's stability at weak Zeeman coupling has been qualitatively overestimated. In the absence of interlayer tunneling, degeneracies occur between total spin multiplets due to the Hamiltonian's invariance under independent spin rotations in top and bottom two-dimensional electron layers.