MIT scientists and colleagues have not only found a new way to manipulate magnetism in a material with light but have also realized a rare form of matter.
Excitons are composed of an electron and a “hole,” or the space left behind when light is shone on a material and energy from a photon causes an electron to jump out of its usual position. Through the mysteries of quantum mechanics, however, the electron and hole are still connected and can “communicate” with each other through electrostatic interactions.
The current work involves the creation of unusual excitons in the material nickel phosphorus trisulfide (NiPS3). These excitons are “dressed” or affected by the environment that surrounds them. In this case that environment is the magnetism.
A magnet works because of a property of electrons called spin (another, more familiar property of electrons is their charge). The spin can be thought of as an elementary magnet, in which the electrons in an atom are like little needles orienting in a certain way. In the magnets on your refrigerator, the spins all point in the same direction, and the material is known as a ferromagnet. In the material used by the MIT team, alternating spins point in opposite directions, forming an antiferromagnet.
The physicists found that a pulse of light causes each of the little electron “needles” in NiPS3 to start rotating around in a circle. The rotating spins are synchronized and form a wave throughout the material, known as a spin wave.
Through their work, the team also demonstrated a rare form of matter. When the physicists exposed NiPS3 to intense pulses of light, they found that it turned into a metallic state that conducts electrons while maintaining its magnetism. NiPS3 is ordinarily an insulator (a material that does not conduct electrons). (Phys.org)
The paper has ben published in Nature Communications.