# Superconducting Levitation

 Superconductors expel magnetic field, and hence repel magnets. This repulsion can be stronger than gravity, which leads to levitation - the most fascinating manifestation of superconductivity. This web-page presents a few movies showing how the superconducting levitation works.

### Movie 1: Levitation in action

A superconductor is immersed in liquid nitrogen to provide cooling below the critical temperature. A magnet is placed in the air above the superconductor and left there levitating. Nothing but magnetic interaction keeps the magnet from falling down.

### Movie 2: Finding a better levitating position

The levitating magnet has a preferential position above the superconductor and returns there after a small perturbation by a human finger. When the magnet is pushed hard towards the superconductor, it changes the magnetic field distribution in the superconductor, and a new position becomes preferential.

### Movie 3: Lifting superconductor without touching it

At room temperature magnetic field lines from the magnet penetrate the superconductor without restraint. After cooling by liquid nitrogen they get trapped by microscopic inhomogeneities in the superconductor. The trapped magnetic lines then serve as invisible threads holding the two objects together at a certain distance.

### Movie 4: Smooth landing during warming up

When the superconductor is taken out of the liquid nitrogen, its temperature slowly starts increasing. As a result, the superconducting properties weaken, and the levitation force gradually gives way to the gravity.

Such a distribution of magnetic field lines is expected for a type-II superconductor with flux pinning, i.e. for all high-temperature superconductors (HTS)

### Schematic visualization of magnetic field lines

Why repulsion?

Magnetic field is partly excluded from the superconductor. Hence, the same repulsion as between a magnet and a diamagnetic.

Why attraction?

The magnetic flux lines that managed to penetrate the superconductor get pinned (trapped) there by microscopic inhomogeneities. When the magnet is lifted up, the superconductor holds its magnetic lines and follows the magnet. How to help magnetic lines penetrate the superconductor? Place the superconductor close to the magnet already at high temperature (movie 3) or push the magnet hard towards the supercondictors (movie 4).

## Levitation with cooling of the magnet and the superconductor apart

#### Description of the movie

• Two objects: a superconductor (the black brick) and a magnet.
• Magneto-optical film is placed on the magnet to visualize its magnetic properties.
• The magnet is placed on the superconductor: no sign of levitation since the superconductor is above the critical temperature.
• Pouring liquid nitrogen which has a temperature of 77 Kelvins (-196 Celsius). The cooling takes a few minutes.
• The magnet is placed above the superconductor: levitation!
• The magnet returns back when pushed aside: the leviation is stable.
• Simple check with a paper sheet: there is nothing but magnetic field between the objects.
• A close view. The magnet is rotating in the air without friction - the idea used in flywheel applications for energy storage.
• Moving the magnet around leads to a redistribution of magnetic field inside the superconductor, which creates various stable positions and orientations for the levitating magnet.
• The superconductor is taken out of the liquid nitrogen followed by its warming up above the critical temperature. The magnet is slowly landing: the levitation is over.

## Levitation with cooling together

#### Description of the movie

• The magnet is located on the superconductor: there is no interaction between them because the superconductor is above the critical temperature.
• The magnet is placed on a glass plate so that its magnetic field penetrate the superconductor.
• Pouring liquid nitrogen which has a temperature of 77 Kelvins (-196 Celsius). The cooling takes a few minutes.
• The glass plate is removed but the magnet continues levitating above the superconductor.
• The magnet is lifted up and the superconductor follows after it as if connected by invisible threads. These threads are magnetic field lines frozen-in in the superconductor and pinned there by microscopic inhomogeneities.
• Repeating the same experiment. Sometimes the magnetic lines get disconnected, and the superconductor falls down. However the magnetic field remains trapped in the superconductor, and the lines re-connect again when the magnet approaches.
• Levitation with slow rotation. Moving a paper sheet demonstrates that there is nothing but magnetic field between the objects.
• The superconductor is taken out of the liquid nitrogen followed by its warming up above the critical temperature. The magnet is falling, the levitation is over.
Published Nov. 30, 2010 2:25 PM - Last modified Apr. 3, 2013 1:30 PM