Broken-symmetry ground states in ν=2 bilayer quantum Hall systems

We report on a study of a bilayer two-dimensional electron gas at Landau-level filling factor v=2. The system exhibits both magnetic and spontaneous interlayer phase coherence broken symmetries. We propose a three-parameter Slater-determinant variational wave function which describes the ground state over the full range of bias-potential (Delta(v)), Zeeman coupling (Delta(z)), and interlayer tunneling amplitude (Delta(t)) strengths. Broken-symmetry states occur inside a volume in this three-dimensional phase diagram near the Delta(z)(2)=Delta(v)(2) +Delta(t)(2) surface. We have obtained analytic results for the intersections of the phase diagram with the Delta(t)=0, Delta(z)=0, and Delta(v)=0 planes and show that the differential capacitance of the bilayer system is singular at the phase boundary. [S0163-1829(99)11935-0].