Moore Foundation grantees at Harvard University have coupled transparent nanometer-scale superconductors to graphene in a new device that could one day be used to build powerful quantum computers.
This work was led by Philip Kim, an experimental investigator in quantum materials through the foundation’s Emergent Phenomena in Quantum Systems (EPiQS) initiative and professor of physics and applied physics at Harvard. Kim and his team made a graphene-based device with superconducting electrodes using a new nanoscale fabrication technique.
In normal conductive materials, such as metals, electrons are slowed by defects in the system, like a ball bouncing off obstacles in a pinball machine. As a result, these defects cause resistance to the flow of electricity. In contrast, superconductors conduct electricity without resistance. Superconductivity occurs because electrons pair up and move through a material as one unit, without any resistance or energy loss.
In graphene, a two-dimensional sheet of carbon atoms that is highly conductive, the electrons typically behave as individual, scattering particles. However, when coupled with superconducting electrodes, the team found the electrons in the graphene paired up in so-called "Andreev states."
Andreev states are electronic configurations that allow a conventional (not superconducting) material to carry an electric current that flows without dissipating energy. The team’s remarkable findings show how a fundamental property of graphene — its ability to conduct electricity —
can be altered by coupling to superconductive electrodes.
These findings, published recently in Nature Physics, help bridge the physics of superconductors to the physics of graphene — two of the most popular topics in condensed matter physics today.
This work also opens new possibilities for topological insulators, materials that allow electrical current to flow with minimal resistance on their surfaces, but not through the bulk. Topological materials were the subject of the 2016 Nobel Prize in Physics.
"The general idea and methodology presented in this work can open a new route towards a universal topological quantum computation," the authors said.
More broadly, Kim’s foundation funding is for building novel quantum materials and searching for exotic quantum phenomena at the interface between dissimilar quantum materials, as exemplified in this study. Co-author Amir Yacoby is also an experimental investigator in quantum materials through the EPiQS initiative.
Read the full article in Nature Physics here, and watch a presentation describing the recent history of graphene by Philip Kim here.
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