High energy spin excitations in YBa_2 Cu_3 O_{6.5}

Abstract

Inelastic neutron scattering has been used to obtain a comprehensive description of the absolute dynamical spin susceptibility ${\chi }^{\prime \prime }(q,\omega )$ of the underdoped superconducting cuprate YBa_2 Cu_3 O_{6.5} ($T_c=52K$) over a wide range of energies and temperatures ($2meV\le \hslash \omega \le 120meV$ and $5K\le T\le 200K$). Spin excitations of two different symmetries (even and odd under exchange of two adjacent CuO_2 layers) are observed which, surprisingly, are characterized by different temperature dependences. The excitations show dispersive behavior at high energies.

15 pages, 5 figures