Nuclear spin-lattice relaxation rate in electron-doped Pr0.91LaCe0.09CuO4 − y: Constraint on the gap symmetry

We present numerical calculations of the nuclear spin-lattice relaxation (Rs)(Rs) rate in the superconducting state of pure indium and slightly underdoped n-type cuprate Pr0.91LaCe0.09CuO4 − y. By properly taking into account electron–phonon coupling, our calculated RsRs for the conventional s  -wave superconductor, indium, is in quantitative agreement the experimental data with a clear Hebel–Slichter peak. In contrast, the absence of the Hebel–Slichter peak in the RsRs data of Pr0.91LaCe0.09CuO4 − y can be explained by either d-wave or highly anisotropic s-wave gap symmetry. Thus, the absence of the Hebel–Slichter peak does not necessarily argue against an s-wave gap symmetry in this electron-doped cuprate.

► Nuclear spin-lattice relaxation rate in electron-doped Pr0.91LaCe0.09CuO4 − y. ► The absence of the Hebel–Slichter peak agrees with either d-wave or anisotropic s-wave. ► The gap symmetry in slightly underdoped n-type cuprates is of highly anisotropic s-wave.