title: Spin-ordering quantum transitions of superconductors in a magnetic field.
abstract: We argue that recent neutron scattering measurements by Lake et al. [Science 291, 1759 (2001)] of the spin excitation spectrum of La(2-delta)Sr(delta)CuO4 in a magnetic field can be understood in terms of proximity to a phase with co-existing superconductivity and spin density wave order. We present a general theory for such quantum transitions, and argue that their low energy spin fluctuations are controlled by a singular correction from the superflow kinetic energy, acting in the region outside the vortex cores. We propose numerous experimental tests of our theory.
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: E
authors.initials: E
authors.lastname: Demler
authors.forename: S
authors.initials: S
authors.lastname: Sachdev
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang