Japanese basket pattern inspires new material

Image source, Felice Frankel / Chelsea Turner
Image caption,
Artwork: the kagome metal is an electrically conducting crystal, made from layers of iron and tin atoms

Researchers have produced a metal with exotic electrical properties by mimicking a pattern from Japanese basket-weaving.

Kagome baskets are characterised by a symmetrical pattern of interlaced, corner-sharing triangles; the pattern has preoccupied physicists for decades.

Metals resembling a kagome pattern on the atomic scale should exhibit peculiar electrical characteristics.

The team behind the first kagome metal has published details in Nature.

Their product is an electrically conducting crystal, made from layers of iron and tin atoms, with each atomic layer arranged in the repeating pattern of a kagome lattice.

When they passed a current across the kagome layers within the crystal, they found that the triangular arrangement of atoms induced strange behaviour in that current.

Instead of flowing straight through, electrons instead veered, or bent back within the lattice.

'Perfect conduction'

This weird behaviour is linked to the physics of the quantum world, which takes over at tiny scales. For example, in quantum mechanics, objects can have the characteristics of both a particle and a wave.

"By constructing the kagome network of iron, which is inherently magnetic, this exotic behaviour persists to room temperature and higher," said co-author Joseph Checkelsky, assistant professor of physics at the Massachusetts Institute of Technology (MIT) in Cambridge, US.

Image source, Takehito Suzuki
Image caption,
Team members stand in front of a two-dimensional kagome pattern

"The charges in the crystal feel not only the magnetic fields from these atoms, but also a purely quantum-mechanical magnetic force from the lattice. This could lead to perfect conduction, akin to superconductivity, in future generations of materials."

The particular quantum behaviour observed is similar to something called the Quantum Hall effect, where electrons flowing through a two-dimensional material will bend into tight circular paths and flow along edges without losing energy.

Physicists have long wondered whether materials could support a form of this exotic Quantum Hall behaviour. But it was only several years ago that researchers made progress in creating them.

Quantum computers

"The community realised, why not make the system out of something magnetic, and then the system's inherent magnetism could perhaps drive this behaviour," said Dr Checkelsky.

The next step was to seek out these characteristics in materials based on a kagome lattice.

Co-author Linda Ye, also from MIT, ground together iron and tin, then heated the resulting powder in a furnace, producing crystals at about 750C - the temperature at which iron and tin atoms prefer to arrange in a kagome-like pattern. She then submerged the crystals in an ice bath to enable the lattice patterns to remain stable at room temperature.

"The kagome pattern has big empty spaces that might be easy to weave by hand, but are often unstable in crystalline solids which prefer the best packing of atoms," she said.

"The trick here was to fill these voids with a second type of atom in a structure that was at least stable at high temperatures. Realising these quantum materials doesn't need alchemy, but instead materials science and patience."

The researchers are now looking at ways to produce other forms of the kagome lattice structures. These could potentially be used as the basis for devices that have zero energy loss, such as dissipationless power lines. They could also find a home in future, more powerful "quantum computers".