Direct Observation of a Superconducting Spin Resonance in the Heavy Fermion Antiferromagnetic Superconductor $UNi_{2}Al_{3}$*

We present neutron scattering data identifying a superconducting spin resonance in the heavy fermion, antiferromagnetic superconductor $UNi_{2}Al_{3}$. This resolves a longstanding issue in the comparison of $UNi_{2}Al_{3}$ to its isostructural sister $UPd_{2}Al_{3}$. Theses material both undergo antiferromagnetic phase transitions at relatively high temperatures, T$_{N}$ = 4.6 K and 14.5 K respectively, before respectively superconducting below 1.2 and 2 K(B. D. Gaulin, et al, PRB 66, 174520 (2002)). However, previous reports suggest that only the magnetic fluctuations in $UPd_{2}Al_{3}$ display sensitivity to superconductivity via a superconducting spin resonance - the build up in the superconducting ground state of excess scattered intensity at a well defined resonance energy centered on a magnetic wave-vector. We resolve this disparity by clearly identifying a superconducting spin resonance in $UNi_{2}Al_{3}$ at the incommensurate wavevector Q = ($\frac{1}{2}$ $\pm$ 0.11 0 $\frac{1}{2}$). This re-establishes the relationship between these sister compounds and further evidences the intimate correlation of magnetism and superconductivity.