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GATE 2024 PH – Question 57

Solid State Physics · superconductivity: type-I and type II superconductors, Meissner effect, London equation, BCS theory, flux quantization. · 2 marks · Multiple select

A material behaves as a superconductor below a critical temperature Tc and as a normal conductor above Tc. A magnetic field B⃗ = Bẑ is applied when T> Tc. The material is then cooled below Tc in the presence of B⃗ . Which of the following figure represent the correct configuration of magnetic field lines?

Four candidate magnetic field configurations across a superconducting transition.
  1. Option A in the figure
  2. Option B in the figure
  3. Option C in the figure
  4. Option D in the figure

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Show answer and explanation

Correct answer: (C) Option C in the figure

Explanation

The Meissner effect expels flux from the superconducting interior even when the field was applied before cooling. C shows external lines bending around the sample.