A type of quantum Hall state requiring nonperturbative Landau-level mixing is argued to arise at low electron density. In these states, up- and down-spin electrons pair to form spinless bosons that condense into a bosonic quantum Hall state. We show that a BCS instability arising in two-component Hall metals stabilizes this paired state at $\nu =2\mathrm{}$. We discuss various experimental implications including a new global phase diagram for the integral quantum Hall effect with spin.

• Received 27 February 1996

DOI:https://doi.org/10.1103/PhysRevB.53.R13275