Evidence for a Transition in the Pairing Symmetry of the Electron-Doped Cuprates La_{2-x}Ce_xCuO_{4-y} and Pr_{2-x}Ce_xCuO_{4-y}

摘要

We present measurements of the magnetic penetration depth, \lambda^{-2}(T),in Pr_{2-x}Ce_{x}CuO_{4-y} and La_{2-x}Ce_{x}CuO_{4-y} films at three Ce dopinglevels, x, near optimal. Optimal and overdoped films are qualitatively andquantitatively different from underdoped films. For example, \lambda^{-2}(0)decreases rapidly with underdoping but is roughly constant above optimaldoping. Also, \lambda^{-2}(T) at low T is exponential at optimal and overdopingbut is quadratic at underdoping. In light of other studies that suggest both d-and s-wave pairing symmetry in nominally optimally doped samples, our resultsare evidence for a transition from d- to s-wave pairing near optimal doping.