There is fractionalization in magic-angle twisted bilayer graphene. Second Bay Studios is a part of Harvard SEAS.
Like elite athletes, exotic quantum particles and phenomena are daring. Only the most extreme conditions will entice the free solo climbers to show up. For exotic phenomena like superconductivity or particles that carry a fraction of the charge of an electron, that means extremely low temperatures or high magnetic fields.
What if you could get these particles to show up in less extreme conditions? The future of quantum materials and applications is dependent on generating exotic fractionally charged particles at low-to-zero magnetic field, even though room-temperature superconductivity is important.
A team of researchers from Harvard University led by Professor of Physics and of Applied Physics at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Ashvin Vishwanath, Professor of Physics in the Department of Physics, are collaborating with Pablo.
Nature publishes the research.
The senior author of the study said that getting exotic particles with low to zero magnetic field is one of the holy grails in the field. There have been theoretical predictions that we should be able to see these strange particles with low to zero magnetic field, but no one has been able to observe it until now.
The researchers were interested in a state of quantum physics. They conduct electricity on their surface or edge, but not in the middle.
quasiparticles are particles that emerge from complex interactions between large numbers of other particles. Sound can be described as a quasiparticle because it comes from the interactions of particles in a material. Like fundamental particles, quasiparticles have defined properties.
The quasiparticles are forced to carry a fraction of the charge of normal electrons because of the strong electron interactions. The fractional particles have strange quantum properties that could be used to create robust quantum bits.
The researchers used two sheets of Graphene twisted together at the magic angle to build their insulator. The first discovered properties of superconductivity in Graphene, as well as states known as Chern bands, which hold great potential to generate fractional quantum states, were shown theoretically by the group at Harvard.
Think of buckets filled with electrons.
"In previous studies, you needed a large magnetic field in order to generate these buckets, which are the topological building blocks you need to get these exotic fractional particles," said Andrew T. Pierce, a graduate student in Yacoby's group and co-first author of the paper. "But magic-angle twist bilayer graphene already has useful topological units built in at zero magnetic field."
To generate fractional states, the researchers need to fill buckets with electrons. All the electrons in a bucket must have the same properties for this to work. They don't in twisted bilayer graphene. electrons have different levels of a property known as the Berry curvature, which causes each electron to experience a magnetic field tied to its particular momentum What isn't in quantum physics?
When filling up the buckets, the electrons' Berry curvature needs to be evened out.
There is a small applied magnetic field.
Yonglong Xie, a graduate student at SEAS and co-first author of the paper, said that they were able to observe a fractional Chern insulator in the twisted bilayer graphene by applying a very small magnetic field. The research sheds light on the importance of the Berry curvature to realize fractionalized exotic states and could point to alterative platforms where Berry curvature isn't as heterogeneous as it is in twisted graphene.
"Twisted bilayer graphene is the gift that keeps on giving and this discovery of fractional Chern insulators is arguably one of the most significant advances in the field," said Vishwanath, senior author of the study. It is amazing to think that this material is the same as your pencil tip.
The senior author of the study said that the discovery of low magnetic field fractional Chern insulators in magic angle twisted bilayer graphene opens a new chapter in the field of topological quantum matter. It offers the possibility of creating and controlling even more exotic quasiparticles known as anyons.
The research was co-authored by many people.
There is more information about the Fractional Chern insulators in magic-angle twisted bilayer graphene. www.nature.com/articles/s41586-021-04002-3
Nature journal information.
Exotic quantum particles need a less magnetic field to be retrieved on December 15, 2021.
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