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Lightning Flashes in Superconductors

By Ross Pomeroy

Superconductors are materials that, when cooled below a critical temperature, will lose all electrical resistance and expel their magnetic fields. This expulsion -- the Meissner effect -- is their defining feature. The effect allows superconductors to, for example, levitate magnets in midair.

Because of their amazing properties, superconductors are used in a wide variety of applications, such as electric motors, generators, digital circuit boards, fusion reactors, maglev trains, magnetic resonance imagers, and microwave technology for mobile phone base stations.

Fascinatingly, superconductors can occasionally and unpredictably suffer very small breakdown events, resembling tiny flashes of lightning. These events coincide with a temporary loss of superconductivity. They're extremely hard to see because they occur in a manner of nanoseconds.

In an attempt to better understand these lightning-like events, researchers conducted a simulation for a small, circular semiconductor. They described one such lightning event in five different stages (see figure below).

First, an unpredictable instability event causes a breakdown to form. It then quickly starts to branch out and increase in temperature (indicated by the bright yellow in row C). The "lightning" stops propagating when heat removal to the substrate eventually balances the heat production.

The cause for these lightning events aren't understood, but the researchers theorize that large fluctuations in both temperature and electric field may be the triggers.

According to the researchers the lightning-like events are "dramatic, irreproducible, and unpredictable," plus they can do damage to devices that utilize superconducting films. That's why it's important to study them.

Source: J. I. Vestgården, D. V. Shantsev, Y. M. Galperin, & T. H. Johansen (2012) Lightning in superconductors. Scientific Reports 2, 886 doi:10.1038/srep00886

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