Question

Which theory best explains the phenomenon of superconductivity?

• A. Drude model
• B. BCS theory
• C. Band theory
• D. Free electron model

Hint:

BCS = Bardeen, Cooper, Schrieffer = Cooper pairs = Superconductivity. Easy to remember, right?

Answer 1

The Correct Option is B

Superconductivity is the phenomenon where certain materials exhibit exactly zero electrical resistance and expel magnetic fields below a specific critical temperature. While many theories attempt to explain electrical conduction, the most widely accepted and accurate theory that explains superconductivity is the BCS theory.
The BCS theory, named after Bardeen, Cooper, and Schrieffer, describes how electrons in a superconductor form paired states known as Cooper pairs. These pairs of electrons move through the lattice without scattering, thus encountering no resistance. This collective behavior of electrons is what allows current to flow indefinitely without energy loss.
Key insights from BCS theory:

• It explains the energy gap in the electronic density of states in superconductors.
• It describes the formation of Cooper pairs due to lattice interactions.
• It successfully accounts for the Meissner effect and critical temperature behavior.

Why other options are incorrect:

• (A) Drude model: Explains conduction in metals using classical free electrons, not suitable for superconductivity.
• (C) Band theory: Describes general conductivity in solids but doesn't explain the zero resistance state.
• (D) Free electron model: Like the Drude model, lacks the quantum treatment needed for superconductivity.

Hence, the BCS theory is the correct and most comprehensive explanation for superconductivity.