A surface barrier in type 2 superconductors is a thin layer of material that prevents the penetration of magnetic fields into the superconductor. It is also known as a "flux barrier" or "magnetic shield".
A surface barrier can enhance the superconducting properties of a type 2 superconductor by trapping the magnetic fields and allowing the material to maintain its superconducting state at higher temperatures and magnetic fields.
The most commonly used materials for creating surface barriers in type 2 superconductors are thin layers of superconducting materials such as niobium or niobium-tin, or non-superconducting materials such as copper, niobium-titanium, or bismuth.
A surface barrier in type 2 superconductors is typically created by depositing a thin layer of the chosen material onto the superconductor using techniques such as sputtering, chemical vapor deposition, or electroplating.
Surface barriers in type 2 superconductors have a wide range of applications, including in magnetic resonance imaging (MRI) machines, particle accelerators, and high-speed trains. They are also used in various research and industrial applications that require strong magnetic fields and low electrical resistance.