ABSTRACT
This chapter discusses the bipolaron problem using the Feynman-Haken path-integral method and the Lee-Low-Pines-Huybrechts method. The idea of bipolaron was first introduced in the polaron literature by Pekar in the early 1950s and was subsequently discussed qualitatively by Schultz. The bipolaron problem is interesting both for academic reasons and for its importance in semiconductor technology. The possibility of superconductivity in an intersite bipolaron gas has been explored by Alexandrov and Collaborators. However, it appears that the bipolaronic superconductivity was suggested much earlier by Schafroth. Depending on the nature and details of the electron-phonon interaction a bipolaron can be large or small. The chapter shows that Frohlich bipolarons can exist in principle in bulk crystals. Lakkis et al. have extended the idea of Anderson to propose intersite bipolarons in the context of elucidating the nature of the three well-differentiated phases and the mechanism of metal-insulator transitions in titanium oxide, which is a mixed valence compound.
