Lecture

The Critical State: Vortex Behavior in Superconductors

Graph Chat

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

In course

MSE-438: Superconducting electronics: A materials perspective

Introduction to superconducting electronic applications and their material requirements, including the fundamental phenomenology of superconductors. Key applications and their material requirements: a) magnets; b) quantum metrology; c) quantum computation. ...

Description

This lecture explores the behavior of vortices in superconductors, focusing on their density in equilibrium and the critical state. It discusses the entry of vortices at the surface, their interaction with pinning sites, and the shielding currents that push them inside. The Bean model is introduced to calculate the magnetic response, emphasizing the importance of geometry and the non-linear problem of critical current. Various models of the critical state are compared, highlighting the limitations and advantages of each. Experimental evidence, including magnetic hysteresis loops and vortex avalanches, is presented to illustrate the complex behavior of vortices in superconducting materials.

Official source

Related concepts (32)

Magnetic hysteresis

Magnetic hysteresis occurs when an external magnetic field is applied to a ferromagnet such as iron and the atomic dipoles align themselves with it. Even when the field is removed, part of the alignment will be retained: the material has become magnetized. Once magnetized, the magnet will stay magnetized indefinitely. To demagnetize it requires heat or a magnetic field in the opposite direction. This is the effect that provides the element of memory in a hard disk drive.

Saturation (magnetic)

Seen in some magnetic materials, saturation is the state reached when an increase in applied external magnetic field H cannot increase the magnetization of the material further, so the total magnetic flux density B more or less levels off. (Though, magnetization continues to increase very slowly with the field due to paramagnetism.) Saturation is a characteristic of ferromagnetic and ferrimagnetic materials, such as iron, nickel, cobalt and their alloys. Different ferromagnetic materials have different saturation levels.

Hysteresis

Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of the moment often form a loop or hysteresis curve, where there are different values of one variable depending on the direction of change of another variable. This history dependence is the basis of memory in a hard disk drive and the remanence that retains a record of the Earth's magnetic field magnitude in the past.

Superconductivity

Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered, even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero.

Magnetic moment

In electromagnetism, the magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. Examples of objects that have magnetic moments include loops of electric current (such as electromagnets), permanent magnets, elementary particles (such as electrons), composite particles (such as protons and neutrons), various molecules, and many astronomical objects (such as many planets, some moons, stars, etc).

Related lectures (32)

Exchange Interaction: Understanding Magnetic Properties

Covers exchange interaction's role in ferromagnetism and its dependence on interatomic distances and Coulomb forces.

Anisotropy and Spin-Orbit Coupling

Explores anisotropy in magnetic materials, spin-orbit coupling effects, and magnetization curves.

Magnetic Hysteresis: Behavior and Loops

Covers magnetic hysteresis, coercive fields, and soft magnetic materials, including the history of coercive fields and interpreting hysteresis curves.

Materials Science of Magnetic Materials

Covers the materials science of magnetic materials, focusing on properties, concepts, and optimization for functional applications.

Vortices: Superconducting Levitation and Type-II Superconductors