Title:
Positive Hall coefficients: not the hole story
(hole should be spelt hole, not whole)
Abstract:
The Hall coefficient measures the voltage induced across a rectanglar bar
when a current flows through the bar and a magnetic field is applied
perpendicular to the bar. The electric field generated by the Hall voltage
counteracts t he force on the moving charge carrier due to the magnetic
field. Positive Hall coefficients are usually associated with materials
where negatively charged electrons are the predominant carrier, whereas
negative Hall coefficients are usually associated with materials, such
as doped semiconductors, where positively charged holes are the
predominant carrier. However we show here that this is not the complete
story. We find it is possible to obtain a material with a negative Hall
coefficient by combining materials with positive Hall coefficients in an
appropriate microstructure. Also we show it is possible to design
microstructures where the effective Hall coefficient is much larger
than the coefficient in any of the constituent phases. The situation is
reminiscent of similar behavior for the effective thermal expansion coefficient,
found by Lakes, Sigmund and Torquato.