Week 2: Linear response (Datta Fig. 2.5)

Linear response: when does f₁ − f₂ become −∂f/∂E? (Datta Fig. 2.5)

The purple curve is the difference of the two Fermi functions divided by y = qV/kT, so its area is always 1. The dashed curve is the thermal broadening function F_T = kT(−∂f/∂E). Shrink y and watch them merge.

y = qV / kT

Datta's values:

Peak of F(E) (F_T peak = 0.25)–

Area under F(E), in units of kT–

Largest gap |F − F_T|–