Incommensurate Magnetic Fluctuations in YBa2Cu3O6.6

Abstract

We use inelastic neutron scattering to demonstrate that at low temperatures, the low frequency magnetic fluctuations in YBa_2Cu_3O_{6.6} ($T_c=62.7$ K) are incommensurate, being found at positions displaced by $\pm \delta$ ($0.057\pm 0.006$ r.l.u.) along the $[\pi ,\pi ]$ direction from the wave vector $(\pi ,\pi )$ associated with the antiferromagnetic order of the parent insulator, YBa_2Cu_3O_{6}. The dynamical susceptibility ${\chi }^{\prime \prime }(q,\omega )$ at the incommensurate positions increases on cooling below $T_c$, accompanied by a suppression of magnetic fluctuations at the commensurate points.

11 pages, Latex, 4 figures