Two- to three-dimensional crossover in the electronic structure of (Bi,Pb)2(Sr,La)2CuO6+delta from angle-resolved photoemission spectroscopy

The hole-concentration (x) dependence of the three-dimensional energy-momentum dispersion in (Bi,Pb)(2)(Sr,La)(2)CuO6+delta has been investigated by angle-resolved photoemission spectroscopy. For a heavily overdoped sample of T-c<= 0.5 K, an energy dispersion of similar to 10 meV in width is observed in the vicinity of the (pi,0) point with varying momentum along the c axis (k(z)). This k(z) dispersion is zero for underdoped, optimally doped, and slightly overdoped samples up to a doping level corresponding to T-c=22 K. At higher doping levels we observe significant dispersion of the order of 10 meV (sample with T-c<= 0.5 K). This is clear evidence that at a doping value corresponding to T-c=22 K, a crossover from two- to three-dimensional electronic structure occurs.