Those terracotta warriors are certainly strange. Beyond protecting a dead Chinese emperor in the afterlife and saving the planet from an alien invasion, they also found a way to nix the third dimension.
The National Magnetic Field Laboratory states the bizarre science starts with a pigment called “Han Purple,” which is a barium copper silicate pigment likely brought over to China from Egypt some 2,000 years ago. The Lab has a very accessible piece of science writing on the discovery, finding that at temperatures approaching absolute zero coupled with high magnetism the pigment’s magnetic waves no longer exist in the third dimension. Read on if you hate the Z-axis (and who doesn’t?).
“It all starts with a pigment called Han purple that was used more than 2,000 years ago to color Xi’an terra cotta warriors of the Qian Dynasty. The pigment is known in the scientific world as BaCuSi206 – and when magnet lab scientists exposed it to very high magnetic fields and very low temperatures, it entered a state of matter that is rarely observed.
“The most recent research, published in today’s issue of the journal Nature, shows that at the lowest temperature point at which the change of state occurs – called the Quantum Critical Point – the Han purple pigment actually loses a dimension: it goes from 3D to 2D. Theoretical physicists have postulated that this kind of dimensional reduction might help explain some mysterious properties of other materials (high temperature superconductors and metallic magnets known as “heavy fermions” for example) near the absolute zero of temperature, but until now, a change in dimension had not been experimentally observed.”
Strap in for some slight technicality:
“The magnetic waves in the pigment exist in a unique state of matter called a Bose Einstein condensate (BEC), so named for its theoretical postulation by Satyendra Nath Bose and Albert Einstein. In the BEC state, the individual waves (associated with magnetism from pairs of copper atoms in BaCuSi2O6) lose their identities and condense into one giant wave of undulating magnetism. As the temperature is lowered, this magnetic wave becomes sensitive to vertical arrangement of individual copper layers, which are shifted relative to each other – a phenomenon known as “geometrical frustration.” This makes it difficult for the magnetic wave to exist in the third up-down dimension any longer, and leads to a change to a two-dimensional wave, in very much the same way as ripples are confined to the surface of a pond. The theoretical framework that leads to this interpretation was provided by Cristian Batista at LANL.”
Bill Rodgers is a Contributing Editor at CFile.
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