We have analyzed the $B_{ 1g}$ and $B_{ 2g}$ Raman spectra of electron-doped cuprate superconductors Nd$_{ 2-x}$Ce$_{ x}$CuO$_4$ and Pr$_{ 2-x}$Ce$_{ x}$CuO$_4$ using a weakly coupled two-band model. One of these two bands is centered around $(\pm \pi/2, \pm \pi/2)$ and couples more strongly with the $B_{ 2g}$ mode, while the other is centered around $(\pm \pi, 0)$ and $(0, \pm \pi)$ and couples more strongly with the $B_{ 1g}$ mode. This model explains in a natural way why the $B_{ 2g}$ Raman peak occurs at a higher frequency than the $B_{ 1g}$ one at optimal doping, and how these two peaks change with doping in agreement with experiments. Our result suggests that the superconducting pairing in electron-doped high-$T_c$ cuprates has the $d_{ x^2-y^2}$-wave symmetry and results from the same mechanism as for hole doped materials.
Categories: cond-mat.supr-con cond-mat.str-el