Type I and Type II Superconductor

The critical temperature (T_C) is an essential parameter dictating the transition of a material into its superconducting state. Below this critical temperature, certain materials exhibit extraordinary properties, conducting electricity without resistance and expelling magnetic fields. This transition marks a fundamental shift in the material’s behavior as electrons pair up to form Cooper pairs, overcoming lattice vibrations to move coherently through the material. Above T_C, however, the material behaves as a regular conductor, with resistance and other conventional characteristics.

The critical magnetic field (H_C) is a defining threshold for the material’s behavior. Beyond this critical value, the superconducting state collapses, and the material reverts to its normal, resistive state. This critical magnetic field represents the limit to which a superconductor can tolerate an applied magnetic field while maintaining its unique properties of zero resistance and perfect diamagnetism. Above (H_C), the magnetic field penetrates the superconductor, disrupting the coherence of the superconducting electron pairs and causing them to decouple, leading to the loss of superconductivity.

There are two types of superconductors – type I and type II. Type I and Type II superconductors differ in their response to magnetic fields, characterized by their critical magnetic fields (H_C) and critical temperatures (T_C).

Type I Superconductors

Here are some characteristics of Type I superconductors.

• These superconductors have a single critical magnetic field (H_C).
• Below their critical temperature (T_C), they expel all magnetic fields from their interior, exhibiting perfect diamagnetism.
• Superconductivity stops once the applied magnetic field exceeds its critical magnetic field, and the material returns to a normal, resistive state.
• Type I superconductors are typically elemental metals like lead and mercury.

Type II Superconductors

Here are some characteristics of Type II superconductors.

• Type II superconductors have two critical magnetic fields (H_C1 and H_C2)
• Below their critical temperature (T_C), they allow some penetration of magnetic fields into their interior.
• H_C1 represents the lower critical magnetic field, where vortices start to penetrate the superconductor, but the bulk remains superconducting.
• H_C2 is the upper critical magnetic field, beyond which the entire material becomes normal.
• The material exists in a mixed state between these two critical fields, allowing for the controlled penetration of magnetic fields.
• Type II superconductors can tolerate higher magnetic fields before losing superconductivity compared to Type I superconductors.
• They are often composed of compound materials, such as certain high-temperature superconductors and alloys like niobium-tin.

The key differences between Type I and Type II superconductors lie in their magnetic properties and critical field strengths. Below is a table summarizing the differences between the two.