Unusual electronic ground state of a prototype cuprate: Band splitting of single CuO2-plane Bi2Sr2-XLaxCuO6+δ

The momentum dependence of the split band of Bi2Sr1.6La0.4CuO6 + δ (Manzke R. et al., Phys. Rev. B, 63 (2001) R100504) is investigated by angle-resolved photoemission spectroscopy with very high resolution along the ΓM-line. The splitting is only observable in this direction and at certain experimental conditions with respect to temperature and doping of the sample and polarization of the impinging radiation. Since bilayer effects cannot be present in this single-layer material and other sources producing a splitting are also less plausible, the results point to an unusual ground state of this system. It is discussed whether microscopic phase separation including striped phase formation, critical fluctuations coupled to electrons (hot spots) or spin charge separation within the Luttinger-liquid picture, leading to the appearance of spinon and holon excitations, is capable to describe the observations qualitatively.