Table of Contents
How does BCS theory explain the origin of superconductivity?
A theory of superconductivity formulated by John Bardeen, Leon Cooper, and Robert Schrieffer. It explains the phenomenon in which a current of electron pairs flows without resistance in certain materials at low temperatures. It is this weak, indirect attraction that binds the electrons together, into a Cooper pair.
How does BCS theory explain important characteristics of superconductors?
Schrieffer (their surname initials providing the designation BCS) to explain the behaviour of superconducting materials. Superconductors abruptly lose all resistance to the flow of an electric current when they are cooled to temperatures near absolute zero.
How does BCS theory explain Meissner effect?
BCS theory correctly predicts the Meissner effect, i.e. the expulsion of a magnetic field from the superconductor and the variation of the penetration depth (the extent of the screening currents flowing below the metal’s surface) with temperature.
What is Meissner effect?
Meissner effect, the expulsion of a magnetic field from the interior of a material that is in the process of becoming a superconductor, that is, losing its resistance to the flow of electrical currents when cooled below a certain temperature, called the transition temperature, usually close to absolute zero.
Do Type 2 superconductors show Meissner effect?
The Meissner effect, a property of all superconductors, was discovered by the German physicists W. Other superconductors, called type II (vanadium and niobium, for example), exhibit only a partial Meissner effect at intermediate magnetic-field strengths no matter what their geometrical shape or size.
What is superconductivity explain the effect of magnetic field on superconductor?
Above the critical temperature, Tc, a superconductor has no notable effect when a magnetic field is applied, as the magnetic field is able to pass through the superconductor unhindered. Since diamagnetics have a magnetization that opposes any applied magnetic field, the superconductor is repelled by the magnetic field.
Is s1015 N S s > perfect conductivity superconductivity?
Persistent current experiments on rings have measured s1015 n s s > Perfect conductivity is not superconductivity Superconductivity is a phase transition A perfect conductor has an infinite relaxation time L/R Resistivity < 10 -23 Ω.cm Decay time > 10 5 years Perfect Diamagnetism ( Meissner & Ochsenfeld 1933 0 B t B =0 Perfect conductor
What are the two types of superconductors?
Two Types of Superconductors • London superconductors (Type II) – λ>> ξ – Impure metals – Alloys – Local electrodynamics • Pippard superconductors (Type I) – ξ>> λ – Pure metals – Nonlocal electrodynamics Material Parameters for Some Superconductors Phenomenological Models (1930s to 1950s)
What is the critical field of a superconductor?
Type I or “soft” superconductors Critical Field ( Type II or “hard” superconductors Expulsion of the magnetic field is complete up to H c1 , and partial up to H c2 Between H c1 and H c2 the field penetrates in the form if quantized vortices or fluxoids 0
What is London penetration depth in superconductors?
• London penetration depth λ – Distance over which magnetic fields decay in superconductors • Pippard coherence length ξ – Distance over which the superconducting state decays Two Types of Superconductors