First, some background
Electrons, the negatively charged particles that orbit an atom's nucleus, have a positively charged counterpart known as a "hole." Essentially, a hole represents the lack of an electron.
When an electron and a hole bind together electrostatically (through something called the Coulomb force), the pair becomes an exciton.
When the excitons (electrons and holes) in a material begin to strongly interact with each other (condense), the material begins to behave like a so-called superfluid, a fluid with zero viscosity that flows without losing any kinetic energy. When stirred, a superfluid will continue to rotate indefinitely.
What did scientists discover?
For their experiments, scientists first created a kind of sandwich: the bread consisted of two "slices" of graphene, a one-atom thick form of carbon that conducts better than copper, and the "filling" was a layer of hexagonal boron nitride (BN), an insulator.
When they put this sandwich in a powerful magnet and an extremely cold environment, they observed some very interesting behaviors. First, they observed excitons that were bound together across the BN layer in a special state called the quantum hall state that occurs in magnetic fields. In addition, the scientists observed the excitons condense into a special kind of superfluid known as a Bose-Einstein condensate (BEC).
These observations were made at the MagLab independently by two different research teams, one from Harvard University and one by Columbia University.
Why is this important?
The observation of a BEC in an engineered geometry that can be tweaked with magnetic and electric fields opens up an exciting new way to study the interactions that govern the pairing of electrons and holes in an engineered geometry. This research result could fundamentally alter existing approaches to electronic design.
Who did the research?
Collaboration A: J.I.A. Li1, T. Taniguchi2, K. Watanabe2, J. Hone1, C.R. Dean1,
Collaboration B: X. Liu3, K. Watanabe4, T. Taniguchi4, B. Halperin3, P. Kim3
1Columbia University; 2National Institute for Materials Science, Japan.
3Harvard University; 4National Institute for Materials Science, Japan.
Why did they need the MagLab?
The research needed the combination of high magnetic fields and low temperatures to achieve the quantum Hall state that would allow the Bose-Einstein condensate to form.
Details for scientists
- View or download the expert-level Science Highlight, Two observations of an exciton condensate in double bilayer graphene
- Read the full-length publication, Excitonic superfluid phase in double bilayer graphene, in Nature Physics.
- Read the full-length publication, Quantum Hall drag of exciton condensate in graphene, in Nature Physics.
This research was funded by the following grants: G.S. Boebinger (NSF DMR-1157490); C.R. Dean (NSF DMR-1507788 & Packard Foundation); P. Kim (DOE DE-SE0012260 & Moore Foundation GBMF4543)
For more information, contact Tim Murphy.