STABILITY OF LARGE BIPOLARONS IN THE PRESENCE OF A MAGNETIC-FIELD

The stability of large bipolarons in the presence of a static magnetic field is investigated on the basis of Feynman's path-integral approac h (although the region of validity of the Jensen-Feynman inequality re mains to be investigated for bipolarons). We find that the magnetic fi eld (characterized by the cyclotron frequency omega(c)) favors bipolar on formation: (i) the critical electron-phonon coupling parameter alph a(c) (above which the bipolaron is stable) decreases with increasing o mega(c) and (ii) the critical Coulomb repulsion strenght U-c (below wh ich the bipolaron is stable) increases with increasing omega(c). The b inding energy and the corresponding variational parameters are calcula ted as a function of alpha, U and omega(c).