Scientists peered into a two-dimensional magnet made of nickel atoms arranged in triangles using a method created by Isidor Isaac Rabi — nuclear magnetic resonance (similar to MRI). Inside, they found magnetic arrows that, in a strong field, froze into an 'up-up-down' pattern, like a formation of soldiers: two steps forward, one step back.
Upon heating, this formation behaved strangely: it kept its order but began to flow, as if the same soldiers were sliding across the field without breaking ranks. This dual state is called supersolid: a substance that is both solid and fluid at the same time, like helium at ultra-low temperatures, discovered by Lev Landau.
Astonishingly, the fluidity emerged precisely upon heating, even though things usually melt. Here, hotter means more disorder (entropy), which goes against conventional logic. Supersolidity was first observed only in 2004 in ultracold atoms, and now it's been found in a magnet at accessible temperatures. This forces a revision of the standard model of quantum states and promises new materials for sensors and quantum devices.
Supersolidity is a paradox: a substance that is simultaneously rigid like ice and flows without friction like superfluid helium. It was first spotted in 2004 in atoms cooled nearly to absolute zero, and now it's been found in a magnet at much higher temperatures.