Someone studying scattering and magnetoresistance argues as follows.
PHYSICS · Multi-part · Fermi University Physics · Condensed Matter, Materials & Soft Matter · Electronic transport in solids · Electronic transport in solids
Solid State Physics, Ch The Boltzmann equation and electrical transport
Problem
Someone studying scattering and magnetoresistance argues as follows.
((a)) "A collision can only destroy some of an electron's forward momentum, never add to it, so the transport time τtr can never be shorter than the collision time τc." Is this correct? Compute the ratio τtr/τc for a scattering process in which every collision turns the electron through exactly 150∘, and say what the result shows about the claim.
((b)) "Consider a two-band metal with an electron band of density ne=3.0×1028m−3 and a hole band of density nh=3.0×1028m−3, with the hole mobility three times the electron mobility. Since it has both electron and hole carriers, like copper it will show a transverse magnetoresistance that saturates at high field." Is this correct? Decide, from the two carrier densities alone, whether this metal's transverse magnetoresistance saturates or not, and explain the reasoning.