6.3 BCS Theory

Question 1

What was the observation that started BCS theory?

Answer 1

Measurements suggested that there was an energy gap, Delta T that existed below T_c

Question 2

Why does an energy gap exist in an insulator?

Answer 2

Due to electron-lattice interactions

Question 3

What does zero resistance imply about the charge carriers?

Answer 3

The charge carriers aren’t interacting with their environment
- There is no available nearby energy state for them to scatter into

Question 4

How did BCS explain the vanishing of the impurity scattering of the charge carriers?

Answer 4

By electron pairings into Cooper pairs

Question 5

Describe when Cooper pairs can be scattered

Answer 5

When there is enough energy to break up the pair

Question 6

When do we get superconductivity in relation to cooper pairs?

Answer 6

When kT < 0.001 eV
2Δ(0) = hf
Em wave absorption and 2 excited electrons

Question 7

How do electrons pair?

Answer 7

Indirectly

• An electron passing through a material can attract a positive ion, which disrupts the ion vibration which can affect another electron
• Lattice effect which can be modelled by the exchange of a phonon between the two electrons