Graphene: Quantum matter creates parts of elementary charge
What we know from school as the smallest charge can further decompose into foreign matter. In fact, magnetic fields are needed for this purpose. But even without that, the effect has now been demonstrated in a material that always surprises us: graphene.
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In graphene, carbon atoms are arranged flat in a hexagonal shape. Even individual layers exhibit amazing quantum mechanical properties, and when stacked on top of each other they are even more surprising.
In some materials, under the influence of magnetic fields, special quasiparticles are formed that carry only a small part of the elementary charge. Like a team about quantum physicists Long Joe from MIT in Cambridge have shown that this works with graphene even without a magnetic field. By stacking the two-dimensional material in a special way, Researchers have called this group anomalous for the first time A truly strange quantum phenomenon.
In the so-called partial quantum Hall effect for its discovery The Nobel Prize in Physics was awarded in 1998, a kind of quantum fluid is created. The electrons of matter combine with components of the magnetic field. As various research groups discovered in 2023, an anomalous variant of the effect can occur in intelligently arranged 2D materials even without a magnetic field; However, graphene does not seem to be suitable for this purpose. The Hall effect was partially quantitative here It was discovered in strong magnetic fields in 2009 And 2021 with weakbut it cannot be done without it.
Long Ju's team initially discovered through theoretical investigations that it might be possible to produce the effect in graphene. The calculations revealed the peculiarity of graphene, which is stacked in five phased layers and sandwiched between two layers of boron nitride. Hexagonal boron nitride is similar to graphene, but in different proportions, and thus creates a pattern of light and dark spots when placed on top of each other. According to the model, this same lattice would affect the electrons inside the graphene in a way similar to the effect of a magnetic field.
Finally, the researchers tried their recipe. They made a graphene-boron nitride sandwich and placed it in their lab's refrigerator, which of course was no ordinary refrigerator: it brought the sample to extremely low temperatures. The movement of electrons is significantly slowed down, enough to form interactions with each other and with the graphene lattice. In fact, measurements of electric current showed an anomalous partial quantum Hall effect, in the absence of an external field!
Graphene is already known for unusual quantum phenomena. Layers twisted relative to each other can conduct electricity without loss. The newly discovered effect will help to better understand these electronic properties. Since Long Ju's initial publication about the experiments The professional community debates the possible microscopic causes. In the future, the researchers hope that it will be easier for applications to correlate different electronic quantum effects in components if they are based on the same material – such as superconductivity and fractional charges in graphene.
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