Beta-Detected NQR in Zero Field with a Low Energy Beam of \nuc{8}{Li}${}^{+}$

Beta-detected nuclear quadrupole resonances (\bnqr) at zero field are observed using a beam of low energy highly polarized radioactive \nuc{8}{Li}${}^{+}$. The resonances were detected in SrTiO${}_3$, Al${}_2$O${}_3$ and Sr${}_2$RuO${}_4$ single crystals by monitoring the beta-decay anisotropy as a function of a small audio frequency magnetic field. The resonances show clearly that \nuc{8}{Li} occupies one site with non-cubic symmetry in SrTiO$_3, two in Al${}_2$O${}_3$ and three sites in Sr${}_2$RuO${}_4$. The resonance amplitude and width are surprisingly large compared to the values expected from transitions between the $\mathrm{\mid }\pm 2>\leftrightarrow \mathrm{\mid }\pm 1>$ spin states, indicating a significant mixing between the $\mathrm{\mid }\pm m>$ quadrupolar split levels.