Localization of electrons due to orbitally ordered bi-stripes in the bilayer manganite La(2-2x)Sr(1+2x)Mn2O7 (x ~ 0.59)

Electronic phases with stripe patterns have been intensively investigated for their vital roles in unique properties of correlated electronic materials. How these real-space patterns affect the conductivity and other properties of materials (which are usually described in momentum space) is one of the major challenges of modern condensed matter physics. By studying the electronic structure of La(2-2x)Sr(1+2x)Mn(2)O(7) (x ～ 0.59) and in combination with earlier scattering measurements, we demonstrate the variation of electronic properties accompanying the melting of so-called bi-stripes in this material. The static bi-stripes can strongly localize the electrons in the insulating phase above T(c) ～ 160 K, while the fraction of mobile electrons grows, coexisting with a significant portion of localized electrons when the static bi-stripes melt below T(c). The presence of localized electrons below T(c) suggests that the melting bi-stripes exist as a disordered or fluctuating counterpart. From static to melting, the bi-stripes act as an atomic-scale electronic valve, leading to a "colossal" metal-insulator transition in this material.