Researchers observed an extremely unexpected behavior in quantum material called frustrated magnets.
These types of magnets should be magnetic at low temperatures, but aren't, which prompted scientists to call them "frustrated," Science Codex reported. The research team found the magnets exhibited the Hall effect, in which a magnetic field applied to an electric current deflects to one side of the semiconductor it flows through. This effect occurs in charged particles, but physicists thought it would be impossible for it to exist in non-charged particles such as those found in frustrated magnets.
"To talk about the Hall Effect for neutral particles is an oxymoron, a crazy idea," said N. Phuan Ong, Princeton's Eugene Higgins Professor of Physics.
These frustrated materials, also called "quantum spin ice," contain magnetic moments should line up in an orderly manner at extremely low temperatures. When this occurs all of their "spins" should point in the same direction, but instead researchers have found they point in random directions.
"These materials are very interesting because theorists think the tendency for spins to align is still there, but, due to a concept called geometric frustration, the spins are entangled but not ordered," Ong said
To see if the Hall effect was present in this type of material, the researchers grew crystals from terbium oxide and titanium oxide. They then attached tiny gold electrodes to either end of each crystal and used microheaters to send heat through them. At the same time a magnetic field was applied in the direction perpendicular to the heat current. The experiments were performed at extremely low temperatures of close to absolute zero. The researchers observed the heat current was deflected to one side of the crystal. The same results occurred when the direction of the heat current was reversed (except it was deflected to the opposite side), which is a representation of the Hall effect.
"All of us were very surprised because we work and play in the classical, non-quantum world," Ong said. "Quantum behavior can seem very strange, and this is one example where something that shouldn't happen is really there. It really exists."
Further experiments could provide insight into how superconductivity occurs in certain copper-containing materials that operate at higher temperatures, some of which are used in technology such as MRI machines. The findings could also reveal whether or not superconductivity could occur in a theoretical particle, called a "spinon," that is the carrier of heat in a quantum system.
"This work sets the stage for hunting the spinon," Ong said. "We have seen its tracks, so to speak."
The findings were published in a recent edition of the journal Science.
