Temperature dependence of the gap size near the brillouin-zone nodes of HgBa2CuO4+δ superconductors

Although more than 20 years have passed, the identification of the superconducting order parameter in cuprates is still under debate. Here, we show that the gap size near the nodes is a good candidate for the order parameter: it scales with the critical temperature T-c over a wide doping range and displays a significant temperature dependence below T-c in both the underdoped and the overdoped regimes. In contrast, the gap size at the antinodes does not scale with T-c in the underdoped regime and appears to be controlled by the pseudogap which persists below T-c.