  Recently, quasi-stationary structures called $E \times B$ staircases were
observed in gyrokinetic simulations, in all transport channels [Dif-Pradalier
et al. Phys. Rev. Lett. 114, 085004 (2015)]. We present a novel analytical
theory - supported by collisional drift-wave fluid simulations - for the
generation of density profile corrugations (staircase), independent of the
action of zonal flows: Turbulent fluctuations self-organize to generate
quasi-stationary radial modulations $\Delta\theta(r,t)$ of the transport
crossphase $\theta$ between density and electric potential fluctuations. The
radial modulations of the associated particle flux drive zonal corrugations of
the density profile, via a modulational instability. In turn, zonal density
corrugations regulate the turbulence via nonlinear damping of the fluctuations.
