On the small enhancement of electric field gradients caused by a deformation potential interaction

We examine the contribution of a deformation potential interaction to elect ric field gradients (EFG) and following quadrupole splitting (Q.S.) in the ground state through the comparison of EFG in the case of no deformation po tential interaction, using Green function evaluated with the first order pe rturbation calculation. The potential V(R) and EFG are derived from the pre ceding Green function. From theoretical results, it is known that enhanceme nt of EFG is caused by a deformation potential interaction and is proportio nal to the number of phonons around a conduction electron (= [N-ph]). The t emperature dependence of V(R), as deduced from the thermal Green function, shows that the EFG increases with temperature. Experimentally, we apply the se theoretical results to the Q.S. of a transition metaldoped beta - FeSi2, especially focusing on that of Go-doped beta - FeSi2. As a result, we obta in [N-ph] similar to 0.07 for Co-doped beta - FeSi2, which is relatively la rge in comparison with that for a typical covalent semiconductor. Compared with [N-ph] for a Ni-doped specimen, the effective mass of a conduction ele ctron is considered to be relatively large in the Go-doped specimen.