Discovering previously unobserved quantum states nested inside the quantum Hall effect in a single-layer form of carbon known as graphene, researchers have found evidence of a new state of matter that challenges scientists’ understanding of collective electron behavior.
First, some background
Graphene is an exciting, Nobel-Prize-winning material that researchers believe may have applications in computers, batteries, cell phones, televisions and even airplanes. A one-atom thick, honeycomb array of carbon atoms, graphene is virtually see-through, yet 300 times stronger than steel and 1,000 times more conducting than silicon.
When a magnetic field is applied perpendicular to the flow of electric current, a transverse voltage develops across the material. Initially discovered in 1879, this is known as the Hall effect. Nearly a century later, researchers earned a Nobel Prize for the uncovering special resistance-free conducting states, quantum in origin, that occur when at very specific magnetic fields. Known as the quantum Hall effect, these states, observed in two-dimensional structures, corresponded to new states of matter.
What did scientists discover?
Working with a unique combination of graphene and boron nitride arranged like a sandwich, scientists at the MagLab observed a new kind of quantum Hall state that does not fit into any existing classes of quantum Hall states. This new phase emerges when strongly interacting electrons move in a spatially periodic structure under the influence of a magnetic field.
Why is this important?
The fractional quantum Hall effect is at the heart of one of the outstanding problems in modern condensed matter physics — understanding how large collections of interacting quantum particles behave together in concert, giving rise to new characteristics that are not a feature of the individual parts. Some fractional quantum Hall states may one day be used as qubits (quantum bits) in future quantum computers or have other exciting applications that scientists can not yet predict.
Why did this research need high fields?
“The combination of large fields, where electron interactions become strong, and low temperature, where small energy gaps can be observed, was crucial,” explains Columbia professor Cory Dean, a collaborator on this research.
Where was this work published?
Science 04 Dec 2015:
Vol. 350, Issue 6265, pp. 1231-1234