Two-dimensional boron is a natural low-temperature superconductor, Rice University scientists have established. In fact, it may be the only 2-D material with such potential. Rice theoretical physicist Boris Yakobson and his co-workers published calculations that show atomically flat boron is metallic and will transmit electrons with no resistance.
The catch, as with most superconducting materials, is that it loses its resistivity only when very cold, in this case between 10 and 20 kelvins (roughly, minus-430 degrees Fahrenheit). But for making very small superconducting circuits, it might be the only game in town.
The basic phenomenon of superconductivity has been known for more than 100 years, said Evgeni Penev, a research scientist in the Yakobson group, but had not been tested for its presence in atomically flat boron.
“Lower dimensionality is also helpful,” Yakobson said. “It may be the only, or one of very few, two-dimensional metals. So there are three factors that gave the initial motivation for us to pursue the research. Then we just got more and more excited as we got into it.“
Electrons with opposite momenta and spins effectively become Cooper pairs; they attract each other at low temperatures with the help of lattice vibrations, the so-called “phonons,” and give the material its superconducting properties, Penev said.
It wasn’t entirely by chance that the first theoretical paper establishing conductivity in a 2-D material appeared at roughly the same time the first samples of the material were made by laboratories in the United States and China. In fact, an earlier paper by the Yakobson group had offered a road map for doing so.
That 2-D boron has now been produced is a good thing, according to Yakobson and lead authors Penev and Alex Kutana, a postdoctoral researcher at Rice.
“In principle, this work could have been done three years ago as well,” he said. “So why didn’t we? Because the material remained hypothetical; okay, theoretically possible, but we didn’t have a good reason to carry it too far.
“But then last fall it became clear from professional meetings and interactions that it can be made. Now those papers are published. When you think it’s coming for real, the next level of exploration becomes more justifiable,” Yakobson said.
Boron atoms can make more than one pattern when coming together as a 2-D material, another characteristic predicted by Yakobson and his team that has now come to fruition. These patterns, known as polymorphs, may allow researchers to tune the material’s conductivity “just by picking a selective arrangement of the hexagonal holes,” Penev said.
He also noted boron’s qualities were hinted at when researchers discovered more than a decade ago that magnesium diborite is a high-temperature electron-phonon superconductor.
Penev suggested that isolating 2-D boron between layers of inert hexagonal boron nitride (aka “white graphene”) might help stabilize its superconducting nature.
Without the availability of a block of time on several large government supercomputers, the study would have taken a lot longer, Yakobson said.
The paper is the first by Yakobson’s group on the topic of superconductivity, though Penev is a published author on the subject.
Original Study: Can Two-Dimensional Boron Superconduct?, Nano Letters (2016). DOI: 10.1021/acs.nanolett.6b00070
Illustration: Electrons with opposite momenta and spins pair up via lattice vibrations at low temperatures in two-dimensional boron and give it superconducting properties, according to new research by theoretical physicists at Rice University. Credit: Evgeni Penev/Rice University
- Quantum Control With Light Paves Way For Ultra-Fast Computers
- Improving Magnesium Borohydride For Solid-state Hydrogen Storage
- Perovskite Solar Cells Have Intrinsic Instability Issues
- Self-powered Mobile Polymers Convert Ultraviolet Light Into Motion
- Graded Bandgap Perovskite Solar Cells Set Efficiency Record