-----------------------------------------------------------------------------

Problem 9

Prove that the expression for the frequency-dependent conductivity in Drude theory in the limit omega*tau>>1 is consistent with that obtained from the Kubo formula if interband transitions are neglected.

Problem 10

Prove that the "band mass" m_b and the "optical mass" m_opt satisfy the inequality

m^*_b/m^*_opt >=S²/S₀²

with S the area of the Fermi surface and S₀ the area of a sphere containing the same number of electron states.
Is this compatible with optical masses being both smaller and larger than band masses? Explain

-----------------------------------------------------------------------------