Inelastic neutron scattering for Nd$_{ 2-x}$Ce$_x$CuO$_{ 4+\delta}$ near optimal doping ($x \approx 0.155$, $T_{ c} = 25 \mathrm{ K}$) reveals that the dynamic magnetic susceptibility at the antiferromagnetic zone center exhibits two characteristic energies in the superconducting state: $\omega_1 \approx 6.4 \mathrm{ meV}$ and $\omega_2 \approx 4.5 \mathrm{ meV}$. These two magnetic energies agree $quantitatively$ with the $B_{ 1g}$ / $B_{ 2g}$ and $A_{ 1g}$ features previously observed in electronic Raman scattering, where the former is believed to indicate the maximum electronic gap and the origin of the smaller $A_{ 1g}$ feature has remained unexplained. The susceptibility change upon cooling into the superconducting state is inconsistent with previous claims of the existence of a magnetic resonance mode near 10 meV, but consistent with a resonance at $\omega_2$.
Categories: cond-mat.supr-con