The Double Exchange Model at Low Densities
CFP and Departamento de F´isica, Faculdade de Ciˆencias Universidade do Porto, 4169-007 Porto, Portugal.(Dated: 2nd February 2008)We obtain the phase diagram of the double-exchange model at low electronic densities in the pres-ence of electron-electron interactions. The single particle problem and its extension to low electronicdensities, when a Wigner crystal of magnetic polarons is generated due to unscreened Coulomb inter-actions, is studied. It is argued that the Wigner crystal is the natural alternative to phase separationwhen the Coulomb interaction is taken into account. We discuss the thermal and quantum stabilityof the crystalline phase towards a polaronic Fermi liquid and a homogeneous, metallic, ferromagneticphase. The relevance and application of our results to EuB
This paper presents a study of the technical efficiency of industries in a transitional economy: China. Using data for 28 manufacturing industries across 29 provinces and the Data Envelopment Analysis approach, the technical efficiency of each industry is measured and compared across regions and provinces. The determinants of differential technical efficiency performance are analysed, with a particular focus on the impact of trade orientation and foreign investment. Trade openness is found generally to have a positive effect on technical efficiency.