Researchers discover novel quantum effect in bilayer graphene

Theorists astatine The University of Texas astatine Dallas, on with colleagues successful Germany, person for the archetypal clip observed a uncommon improvement called the quantum anomalous Hall effect successful a precise elemental material. Previous experiments person detected it lone successful analyzable oregon delicate materials.

Dr. Fan Zhang, subordinate prof of physics successful the School of Natural Sciences and Mathematics, is an writer of a survey published connected Oct. 6 successful the diary Nature that demonstrates the exotic behaviour successful bilayer graphene, which is simply a people occurring, two-atom bladed furniture of c atoms arranged successful 2 honeycomb lattices stacked together.

The quantum Hall effect is simply a macroscopic improvement successful which the transverse absorption successful a worldly changes by quantized values successful a stepwise fashion. It occurs successful two-dimensional electron systems astatine debased temperatures and nether strong magnetic fields. In the lack of an outer magnetic field, however, a 2D strategy whitethorn spontaneously make its ain magnetic field, for example, done an orbital ferromagnetism that is produced by interactions among electrons. This behaviour is called the quantum anomalous Hall effect.

"When the uncommon quantum anomalous Hall effect was investigated previously, the materials studied were complex," Zhang said. "By contrast, our worldly is comparably simple, since it conscionable consists of 2 layers of graphene and occurs naturally."

Dr. Thomas Weitz, an writer of the survey and a prof astatine the University of Göttingen, said: "Additionally, we recovered rather counterintuitively that adjacent though c is not expected to beryllium magnetic oregon ferroelectric, we observed experimental signatures accordant with both."

In probe published successful 2011, Zhang, a theoretical physicist, predicted that bilayer graphene would person 5 competing crushed states, the astir unchangeable states of the worldly that hap astatine a somesthesia adjacent implicit zero (minus 273.15 degrees Celsius oregon minus 459.67 degrees Fahrenheit). Such states are driven by the communal enactment of electrons whose behaviour is governed by quantum mechanics and quantum statistics.

"We predicted that determination would beryllium 5 families of states successful bilayer graphene that vie with each different to beryllium the ground state. Four person been observed successful the past. This is the past 1 and the astir challenging to observe," Zhang said.

In experiments described successful the Nature article, the researchers recovered 8 antithetic crushed states successful this 5th household that grounds the quantum anomalous Hall effect, ferromagnetism and ferroelectricity simultaneously.

"We besides showed that we could take among this octet of crushed states by applying tiny outer electrical and magnetic fields arsenic good arsenic controlling the motion of complaint carriers," Weitz said.

The quality to power the physics properties of bilayer graphene to specified a precocious grade mightiness marque it a imaginable campaigner for aboriginal low-dissipation quantum accusation applications, though Zhang and Weitz said they are chiefly funny successful revealing the "beauty of cardinal physics."

"We predicted, observed, elucidated and controlled a quantum anomalous Hall octet, wherever 3 striking quantum phenomena—ferromagnetism, ferroelectricity and zero-field quantum Hall effect —can coexist and adjacent cooperate successful bilayer graphene," Zhang said. "Now we cognize we tin unify ferromagnetism, ferroelectricity and the quantum anomalous Hall effect successful this elemental material, which is astonishing and unprecedented."

Other authors of the Nature nonfiction see UT Dallas physics doctoral pupil Tianyi Xu and researchers from the University of Göttingen and the Ludwig Maximilian University of Munich.

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