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Physicists discover completely new quantum states when graphene meets



The super-thin & # 39; wonder material & # 39; Graphene has upset science for years with its amazing features, but it gets really interesting to stack that 2D nanomaterial against itself.

In recent experiments, physicists in the US have found that proximity to previously unobserved quantum states results when graphene is assembled in a double-layered vertical stack – with two adjacent layers of material almost touching each other.

These newly measured states, which result from complex interactions of electrons between the two graphene layers, are examples of the so-called fractional quantum Hall effect – and this is only the recent example of how natural sciences become funny when materials are effective only two prove dimensions.

"The results show that stacking 2D materials in close proximity leads to completely new physics," says physicist Jia Li of Brown University.

"In terms of materials science, this work shows that these layered systems are possible. It makes sense to develop new types of electronic devices that use these new quantum Hall states."

The roots of the new discovery go back 1

40 years later, scientists first discovered the so-called Hall effect: the way in which the voltage can be deflected by the presence of a magnetic field.

This so-called Hall voltage transversally passes through the Hall effect, which is amplified as the applied magnetic field becomes stronger.

About a century later, physicists observed a similar phenomenon, the quantum Hall effect, which can be observed in two-dimensional electron systems – including newer 2D nanomaterials such as graphene.

In the quantum version of the effect It was found that the amplification of the Hall effect by stronger magnetic fields was not a smooth, linear increase: Instead, the Hall conductivity was quantized – a jump to new, solid plateaus, similar to a staircase.

Experiments have shown that some of these phenomena can be explained by fractional numbers – the above-mentioned fractional quantum Hall effect (FQHE). Li's team has now observed new types of FQHE in his study.

"Once again, Graphen's incredible versatility has allowed us to push the boundaries of device structures beyond what we've been able to do," says one of the team members, physicist Cory Dean of Columbia University.

"The precision and tunability with which we can manufacture these devices now enables us to explore a whole field of physics that has recently been considered completely inaccessible."

Two graphene layers were separated by a thin layer of hexagonal boron nitride, which was used as an insulating barrier. The device was also surrounded by hexagonal boron nitride and connected to graphite electrodes.

By exposing this aggregate to extremely strong magnetic fields – a million times stronger than the Earth's magnetic field – the team observed unprecedented FQHE states in the interaction of electrons between the graphene layers.

While these fascinating states are new to science, they seem largely consistent with our existing understanding of quasiparticles, termed compound fermions – a quantized phenomenon first discovered in FQHE research) as we thought.

"Apart from the interlayer composite fermions, we have observed other features that can not be explained in the composite Fermion model," says physicist Qianhui Shi of Columbia University.

To our surprise, these new states result from the pairing of compound fermions. "

There is still much to explore before we understand the f The team states" to interpret these states as the result of residual pairing interactions between CFs that represent a new type of correlated ground state that applies only to graphene bilayer structures and is not described by the conventional CF model. "

In other words, one graphene layer is good, but two are not of this world.

The results are reported in Natural Physics .


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