The researchers also discovered, to their own surprise, that two pieces of the material do not need to be physically connected for the effect to propagate from one to the other.
They scraped away a portion of the sample with a file, to create two pieces of material separated by a tiny gap. If the spin effect were caused by electrical conduction that is, electrons flowing from one part of the material to the other then the gap would block the effect from spreading. Again, they applied heat to one side.
The effect persisted.
"We figured that each piece would have its own distribution of spin-up and spin-down electrons," said Myers. "Instead, one side of the first piece was spin up, and the far side of the second piece was spin down. The effect somehow crossed the gap."
"The original spin-Seebeck detection by the Tohoku group baffled all theoreticians," Heremans added. "In this study, we've independently confirmed those measurements on a completely different material. We've proven we can get the same results as the Tohoku group, even when we take the measurements on a sample that's been separated into two pieces, so that electrons couldn't possibly pass between them."
Despite these new experiments, the origin of the spin-Seebeck effect remains a mystery.
|Contact: Joseph Heremans|
Ohio State University