Dimov, IvailoHalperin, BertrandNayak, Chetan2009-06-172008Dimov, Ivailo, Bertrand I. Halperin, and Chetan Nayak. 2008. Spin order in paired quantum Hall states. Physical Review Letters 100, no. 12: 126804.0031-9007http://nrs.harvard.edu/urn-3:HUL.InstRepos:3110942We consider quantum Hall states at even-denominator filling fractions, especially nu=5/2, in the limit of small Zeeman energy. Assuming that a paired quantum Hall state forms, we study spin ordering and its interplay with pairing. We give numerical evidence that at nu=5/2 an incompressible ground state will exhibit spontaneous ferromagnetism. The Ginzburg-Landau (GL) theory for the spin degrees of freedom of paired Hall states is a perturbed CP² model. We compute the coefficients in the GL theory by a BCS Stoner mean-field theory for coexisting order parameters, and show that even if repulsion is smaller than that required for a Stoner instability, ferromagnetic fluctuations can induce a partially or fully polarized superconducting state.en-US10.1103/PhysRevLett.100.126804