Diamagnetism of dielectrics

An expression is derived for the magnetic susceptibility of an intrinsic semiconductor in a tight-binding basis that is valid for both crystalline and amorphous materials. In addition to diamagnetic intraband terms proportional to the square of the tight-binding radii there are interband terms involving intersite matrix elements. These additional terms are evaluated for a simple two-band model and found to be paramagnetic. It is shown that in an amorphous material these paramagnetic intersite contributions will be reduced, thereby producing a diamagnetic enhancement.