New analysis uncovers unique electron crystal in graphene

Researchers from the College of British Columbia, the College of Washington, and Johns Hopkins College have recognized a brand new class of quantum states in a custom-engineered graphene construction.

Revealed in Nature, the examine experiences the invention of topological digital crystals in twisted bilayer–trilayer graphene, a system created by introducing a exact rotational twist between stacked two-dimensional supplies.

“The place to begin for this work is 2 flakes of graphene, that are made up of carbon atoms organized in a honeycomb construction. The way in which electrons hop between the carbon atoms determines {the electrical} properties of the graphene, which finally ends up being superficially just like extra frequent conductors like copper,” mentioned Prof. Joshua People, a member of UBC’s Physics and Astronomy Division and the Blusson Quantum Matter Institute (UBC Blusson QMI).

“The subsequent step is to stack the 2 flakes along with a tiny twist between them. This generates a geometrical interference impact often known as a moiré sample: Some areas of the stack have carbon atoms from the 2 flakes instantly on high of one another, whereas different areas have the atoms offset,” People mentioned.

“When electrons hop by this moiré sample within the twisted stack, the digital properties are completely modified. For instance, the electrons gradual method down, and generally they develop a twist of their movement, just like the vortex within the water on the drain of a tub as it’s draining out.”

The breakthrough discovery reported on this examine was noticed by an undergraduate scholar, Ruiheng Su, from UBC, finding out a twisted graphene pattern ready by Dr. Dacen Waters, a postdoctoral researcher within the lab of Prof. Matthew Yankowitz on the College of Washington.

Whereas engaged on the experiment in People’s lab, Ruiheng found a novel configuration for the system the place the electrons within the graphene froze into a superbly ordered array, locked in place but twirling in unison like ballet dancers gracefully performing stationary pirouettes. This synchronized rotation offers rise to a exceptional phenomenon the place electrical present flows effortlessly alongside the sides of the pattern whereas the inside stays insulating as a result of the electrons are immobilized.

Remarkably, the quantity of present that flows alongside the sting is exactly decided by the ratio of two elementary constants of nature—Planck’s fixed and the cost of the electron. The precision of this worth is assured by a property of electron crystal often known as topology, which describes the properties of objects that stay unchanged by modest deformations.

“Simply as a donut can’t be easily deformed right into a pretzel with out first reducing it open, the circulating channel of electrons across the boundary 2D electron crystal stays undisturbed by dysfunction in its surrounding setting,” mentioned Yankowitz.

“This results in a paradoxical habits of the topological digital crystal not seen in typical Wigner crystals of the previous—regardless of the crystal forming upon freezing electrons into an ordered array, it could actually however conduct electrical energy alongside its boundaries.”

An on a regular basis instance of topology is the Möbius strip—a easy but mind-bending object. Think about taking a strip of paper, forming it right into a loop, and taping the ends collectively. Now, take one other strip, however earlier than becoming a member of the ends, give it a single twist. The result’s a Möbius strip, a floor with only one facet and one edge. Amazingly, regardless of the way you attempt to manipulate the strip, you can’t untwist it again into a standard loop with out tearing it aside.

The rotation of the electrons within the crystal is analogous to the twist within the Möbius strip, and results in a exceptional attribute of a topological digital crystal by no means earlier than seen within the uncommon circumstances the place electron crystals have been noticed up to now: edges the place electrons stream with out resistance, described as being locked in place throughout the crystal itself.

The topological electron crystal will not be solely fascinating from a conceptual viewpoint but additionally opens up new alternatives for developments in quantum info. These embody future makes an attempt to couple the topological electron crystal with superconductivity, forming the inspiration of qubits for topological quantum computer systems.