Superconductors promise a revolution in technology — from levitating trains to powerful particle accelerators and medical scanners. However, their operation is limited by a fragile balance: too strong a current or magnetic field destroys the state in which electricity flows without resistance.
In conventional direct-current measurements this limit is hard to reach. It is outpaced by quantum vortices — tiny "tornadoes" of magnetic flux that arise in type-II superconductors and quickly cause heating and resistance.
Scientists from the Max Planck Institute in Hamburg found a way to bypass this obstacle. They used laser pulses with a duration of 300 femtoseconds, which turned into electrical pulses of just a few picoseconds. During that time the vortices did not manage to shift and disrupt the superconductivity.
In the experiment, niobium nitride withstood a current 2,2 times higher than the usual critical value, and then the superconductivity abruptly ceased — which is exactly how it should happen when Cooper pairs are broken. In a material based on yttrium-barium-copper oxide, the process proceeded more smoothly because of a different symmetry of the energy gap.
The new method makes it possible to directly measure the fundamental properties of materials that are inaccessible under conventional measurements. It opens the way to testing many superconductors at their true limits and to creating more robust devices.
The study was published in Nature Physics and shows that speed sometimes decides everything: it is enough to outrun quantum processes to see what a material is truly capable of.
