Charge and orbital order in half-doped manganites

An explanation is given for the charge order, orbital order and insulating state observed in half-doped manganese oxides, such as Nd$_{1/2}$Sr$_{1/2}$MnO$_{3}$. The competition between the kinetic energy of the electrons and the magnetic exchange energy drives the formation of effectively one-dimensional ferromagnetic zig-zag chains. Due to a topological phase factor in the hopping, the chains are intrinsically insulating and orbital-ordered. Most surprisingly, the strong Coulomb interaction between electrons on the same Mn-ion leads to the experimentally observed charge ordering. For doping less than 1/2 the system is unstable towards phase separation into a ferromagnetic metallic and charge-ordered insulating phase.Comment: To appear in Phys. Rev. Lett., 4 pages, 4 figure

Ouverture de ‘Global Networks and Local Development-2’

The global boundaries of innovation, creative imitation and imitation have significantly changed the relative position of many Nation-States and their competitive positions face to global networks and local firms’ development. Chinese production organisations, not casually, are actually involved in the global economic growth as a process of continuous technological innovation and industrial upgrading (creative imitation), with a massive engagement in the local development. Globalization shifted also India to become an important R&D hub in many industries. After years of self-imposed exclusion (for the long, post-colonial license orientation) India has gone beyond the limit of reverse engineering of products developed elsewhere (creative imitation) and has finally joined the global business of innovation and imitation. Finally, the growth model of Italian businesses abroad is consistent with the characteristics of Italian designer products and the country’s fragmented industrial structure, which are reflected in a ‘global gap’. Italian firms are therefore progressively oriented to confine their competitive policies to internal markets, with productions focused on imitation and creative imitation