| Abstract: | The striped phase, a novel type of electron solid, has been observed recently in a number of doped Mott-Hubbard insulators (including cuprates). This solid consists of a parallel array of charged-domain walls, bound states of carriers and Néel walls in the antiferromagnetic spin system. The existence of these states has been predicted well in advance of their experimental observation on the basis of semiclassical (‘Hartree-Fock’) theory. Nevertheless, it is not at all clear whether semiclassics yields a correct explanation. In this paper we will focus especially on the variety of striped phases realized in the cuprates, characterized by a domain wall filling of half a hole per domain wall unit cell. We will unfold the reasons why semiclassics, as applied to simple Hubbard models, favours strongly a filling of one hole per domain wall unit cell, as is for instance the case in the nickelates. Nevertheless, the occurrence of half-filled walls as semiclassical ground states cannot be excluded on general grounds. It might be that Hubbard models do not incorporate the microscopic situation correctly. Instead, we derive a qualitative criterion: in order to acquire a special stability on the semiclassical level, the half-filled domain walls should be characterized by a quadrupling of the period along the walls, involving a modulation in the longitudinal spin- and/or charge channel. 64.60. - i, 71.27. + a, 74.72. - h, 75.10. - b |
