Campbell Response in Type-II Superconductors under Strong Pinning Conditions.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• The ac magnetic response of type II superconductors is crucial for understanding their flux pinning properties.
• The pinning landscape dictates critical current density and magnetic flux penetration.

Purpose of the Study:

• To derive a microscopic expression for the Campbell length (λ(C)) using strong pinning theory.
• To elucidate the relationship between Campbell length, pinning force, and pinning energy.
• To investigate differences in Campbell length for zero-field-cooled and field-cooled samples.

Main Methods:

• Application of strong pinning theory to derive the Campbell length.
• Analysis of the dependence of λ(C) on the jump in pinning force.
• Comparison of theoretical predictions with experimental data.

Main Results:

• A microscopic expression for the Campbell length (λ(C)) was derived.
• Campbell length is shown to be determined by the jump in pinning force, not pinning energy.
• Significant differences in λ(C) were observed between zero-field-cooled and field-cooled samples.
• Hysteretic behavior is predicted for field-cooled samples.

Conclusions:

• The Campbell length provides a direct probe of the pinning force landscape in superconductors.
• The ac magnetic response technique offers a novel method for characterizing superconductor pinscapes.
• Understanding the differences between cooled states is essential for superconductor applications.