Natural 3D counterpart to graphene discovered

Scientists have discovered a 3D version of graphene, an advance that may lead to the development of faster transistors and far more compact hard drives.
A collaboration of researchers at the US Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) has discovered that sodium bismuthate can exist as a form of quantum matter called a three-dimensional topological Dirac semi-metal (3DTDS).
This is the first experimental confirmation of 3D Dirac fermions in the interior or bulk of a material, a novel state that was only recently proposed by theorists.
"A 3DTDS is a natural three-dimensional counterpart to graphene with similar or even better electron mobility and velocity," said Yulin Chen, a physicist with Berkeley Lab's Advanced Light Source (ALS) when he initiated this study, and now with the University of Oxford.

"Because of its 3D Dirac fermions in the bulk, a 3DTDS also features intriguing non-saturating linear magnetoresistance that can be orders of magnitude higher than the materials now used in hard drives, and it opens the door to more efficient optical sensors," Chen said.
Two of the most exciting new materials in the world of high technology today are graphene and topological insulators, crystalline materials that are electrically insulating in the bulk but conducting on the surface.

Both feature 2D Dirac fermions (fermions that aren't their own antiparticle), which give rise to extraordinary and highly coveted physical properties.
"The swift development of graphene and topological insulators has raised questions as to whether there are 3D counterparts and other materials with unusual topology in their electronic structure," said Chen.

"Our discovery answers both questions. In the sodium bismuthate we studied, the bulk conduction and valence bands touch only at discrete points and disperse linearly along all three momentum directions to form bulk 3D Dirac fermions," he said.
Sodium bismuthate is too unstable to be used in devices without proper packaging, but it triggers the exploration for the development of other 3DTDS materials more suitable for everyday devices, a search that is already underway.
Sodium bismuthate can also be used to demonstrate potential applications of 3DTDS systems, which offer some distinct advantages over graphene.
"A 3DTDS system could provide a significant improvement in efficiency in many applications over graphene because of its 3D volume," Chen said.

The study is published in the journal Science.