Doping dependence of the gap anisotropy in La2-xCexCuO4 studied by millimeter-wave spectroscopy -: art. no. 054511

We measure the penetration depth of optimally doped and underdoped La2-xCexCuO4 in the millimeter frequency domain (4-7 cm-1) and for temperatures 2 Kless than or equal toTless than or equal to300 K. The penetration depth as a function of temperature reveals significant changes on electron doping. It shows quadratic temperature dependence in underdoped samples, but increases almost exponentially at optimal doping. Significant changes in the gap anisotropy (or even in the gap symmetry) may account for this transition.