Type-II superconductors exhibit a 'mixed state' between \( H_{c1} \) (lower critical magnetic field) and \( H_{c2} \) (upper critical magnetic field), which means:
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In Type-II superconductors, think of the magnetic field slipping in through narrow “tubes” — those are the quantized vortices that define the mixed state!
The material alternates between superconducting and normal conducting regions
Cooper pairs break down entirely
Magnetic flux partially penetrates the material in the form of quantized vortices
The material's critical temperature (Tc) fluctuates
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The Correct Option isC
Solution and Explanation
Type-II superconductors, unlike Type-I, do not completely expel magnetic fields above a certain point. Instead, they enter what is called a mixed state or vortex state between the lower and upper critical magnetic field limits, denoted as \( H_{c1} \) and \( H_{c2} \). Key Features of the Mixed State:
When the external magnetic field is between \( H_{c1} \) and \( H_{c2} \), the magnetic field begins to penetrate the material in the form of quantized magnetic flux lines, also called flux vortices.
Each vortex carries one quantum of magnetic flux and is surrounded by circulating superconducting currents.
The rest of the material remains superconducting, creating a unique state where magnetic and superconducting regions coexist.
This makes Type-II superconductors very useful in high-field applications, such as in MRI machines and particle accelerators.
Why the Other Options Are Incorrect:
(A) There is no alternation between regions — rather, magnetic flux smoothly enters in vortex form.
(B) Cooper pairs do not completely break down in this state; they remain intact in the regions between vortices.
(D) The critical temperature remains constant for a given material — it is not affected by the magnetic field in this manner.
Thus, the correct answer is: Magnetic flux partially penetrates the material in the form of quantized vortices.