Magnetite is the oldest magnetic material known to humans, yet researchers are still mystified by certain aspects of its properties.
For example, when the temperature is lowered below 125 kelvins, magnetite changes from a metal to an insulator, its atoms shift to a new lattice structure, and its charges form a complicated ordered pattern. This extraordinarily complex phase transformation, which was discovered in the 1940s and is known as the Verwey transition, was the first metal-insulator transition ever observed. For decades, researchers have not understood exactly how this phase transformation was happening.
According to a paper published March 9 in Nature Physics, an international team of experimental and theoretical researchers discovered fingerprints of the quasiparticles that drive the Verwey transition in magnetite. Using an ultrashort laser pulse, the researchers were able to confirm the existence of peculiar electronic waves that are frozen at the transition temperature and start “dancing together” in a collective oscillating motion as the temperature is lowered.
“We were investigating the mechanism behind the Verwey transition and we suddenly found anomalous waves freezing at the transition temperature” said MIT physics postdoc Edoardo Baldini, one of the lead authors on the paper. “They are waves made of electrons that displace the surrounding atoms and move collectively as fluctuations in space and time.”
Source: “Dancing electrons solve a longstanding puzzle in the oldest magnetic material”, Sandi Miller, MIT Department of Physics