Intrinsic electronic Raman spectrum and pairing symmetry in cuprate superconductors

Since the polarized electronic Raman scattering (ERS) measures the characteristics of the bulk rather than the surface, ERS data generate more accurate information. An ERS theory¹⁾ is that, when d_x2-y2-wave symmetry is assumed, I(ω) ≈ω, linear behaviour in the B_2g mode and II(ω) ≈ω³ for the B_1g mode were calculated below an energy gap. ERS experiments^1,2) showed the linear behaviour in the B_2g mode of the node area below T_c for underdoped cuprate crystals. This is evidence of d-wave symmetry. However, since the measured data in inhomogeneous crystals with at least two phases has an averaged effect of the two phases to the measurement region, the measured data should be decomposed to analyze the intrinsic property. The ERS data well decomposed in an electron-doped cuprate Pr_2-xCe_xCuO_4-δ²⁾ allow us to demonstrate the intrinsic effect. Here, we show the intrinsic nonlinear Raman spectrum obtained by subtracting the pseudogap characteristic of a nonlinear from the linear Raman spectrum measured in the B_2g mode of the node area below T_c. The intrinsic nonlinear behaviour implies the existence of the nodal superconducting gap denying d-wave pairing symmetry. 1) PRL 72, 396 (1994). 2) PRB 72, 214510 (2005).