Jan
21
A New 3D Material Discovery May Speed Up Electronics
January 21, 2014 | Leave a Comment
A 3 dimensional (3D) version of graphene, the 2 dimensional (2D) sheets of carbon through which electrons race at many times the speed as they move through silicon has been discovered. The discovery 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.
Yulin Chen, formerly a physicist with Berkeley Lab’s Advanced Light Source (ALS) when he initiated the study that led to this discovery, and now with the University of Oxford said, “A 3DTDS is a natural three-dimensional counterpart to graphene with similar or even better electron mobility and velocity. 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 is the corresponding author of a paper in Science reporting the discovery. The paper is titled “Discovery of a Three-dimensional Topological Dirac Semimetal, Na3Bi.” Co-authors were Zhongkai Liu, Bo Zhou, Yi Zhang, Zhijun Wang, Hongming Weng, Dharmalingam Prabhakaran, Sung-Kwan Mo, Zhi-Xun Shen, Zhong Fang, Xi Dai and Zahid Hussain.
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. Topological insulators also possess a unique electronic structure, in which bulk electrons behave like those in an insulator while surface electrons behave like those in graphene.
Topological Dirac Semi Metal Critical Point Graphic. Click image for more info.
Chen explains, “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. 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. Furthermore, the topology of a 3DTSD electronic structure is also as unique as those of topological insulators.”
The suggestion for electronic engineers is a better material that uses less current and generates less heat running at far higher speeds.
The discovery was made at the Advanced Light Source (ALS), a Department of Energy national user facility housed at Berkeley Lab, using beamline 10.0.1, which is optimized for electron structure studies. The collaborating research team first developed a special procedure to properly synthesize and transport the sodium bismuthate, a semi-metal compound identified as a strong 3DTDS candidate by co-authors Fang and Dai, theorists with the Chinese Academy of Sciences.
At ALS beamline 10.0.1, the collaborators determined the electronic structure of their material using Angle-Resolved Photoemission Spectroscopy (ARPES), in which x-rays striking a material surface or interface cause the photoemission of electrons at angles and kinetic energies that can be measured to obtain a detailed electronic spectrum.
“ALS beamline 10.0.1 is perfect for exploring new materials, as it has a unique capability whereby the analyzer is moved rather than the sample for the ARPES measurement scans,” Chen says. “This made our work much easier as the cleaved sample surface of our material sometimes has multiple facets, which makes the rotating-sample measurement schemes typically employed for ARPES measurements difficult to carry out.”
Sodium bismuthate is too unstable to be used in devices without proper packaging, but it has triggered 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.
Chen added, “A 3DTDS system could provide a significant improvement in efficiency in many applications over graphene because of its 3D volume. Also, preparing large-size atomically thin single domain graphene films is still a challenge. It could be easier to fabricate graphene-type devices for a wider range of applications from 3DTDS systems.”
Chen also points out another realm of great interest. The 3DTDS system also opens the door to other novel physical properties, such as giant diamagnetism that diverges when energy approaches the 3D Dirac point, quantum magnetoresistance in the bulk, unique Landau level structures under strong magnetic fields, and oscillating quantum spin Hall effects. All of these novel properties can be a boon for future electronic technologies. Future 3DTDS systems can also serve as an ideal platform for applications in spintronics.
This news might not seem big, but it’s definitely something worthy of continued observation as the potential in electrical current use, heat generation, computational power, memory density and other costs in electronics, particularly data and information storage and management would be very favorably affected in electrical power reductions and much increased total capacity.
It is the beginning of much bigger news to come.
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