ARPES Reveals Gap Evolution in La(2-x)Sr(x)CuO4by Tommy on 16/07/2012
Evolution from a nodeless gap to dx2-y2 form in underdoped La2-xSrxCuO4, E. Razzoli, G. Drachuck, A. Keren, M. Radovic, N. C. Plumb, J. Chang, J. Mesot and M. Shi
To summarize, our main experimental findings are: 1) for highly underdoped LSCO (x = 0:08), in the superconducting state the electronic excitations are gaped along the entire underlying FS; 2) the diagonal gap persists above Tc while increasing the temperature and/or reducing the hole-concentration; 3) whereas the gap size on zone boundary remains constant up to 150 K, the diagonal gap is temperature-dependent; 4) when the diagonal gap decreases to zero, it leaves behind a pure dx2-y2 energy gap, at which point a Fermi arc emerges and its length increases with temperature. Our observations in highly underdoped LSCO could be explained either by a strong fluctuating competing order which is different from the superconducting order parameter , or by a mixed dx2-y2 + idxy gap function occurring when the doping is below a quantum critical point . The entirely gapped Fermi surface in highly underdoped LSCO is a profound departure from the dx2-y2 form observed at moderate to high doping. Further investigations of the origins of this nodeless gap function and its evolution to pure dx2-y2 form promise to shed light on how superconductivity emerges from the Mott insulating state in high-Tc cuprates.