When layers of "magic-angle" graphene come in contact with layers of certain metals, it creates a phenomenon called spin-orbitcoupling. ferromagnetism is a result of that phenomenon. The Li Lab is located at Brown University.
It gives rise to some fascinating physics when two sheets of carbon nanotubes are stacked together at a certain angle. When this so-called "magic-angle graphene" is cooled to zero, it becomes a superconductor, meaning it conducts electricity with zero resistance.
A research team from Brown University found a new phenomenon in magic-angle graphene. The team showed that by inducing a phenomenon known as spin-orbitcoupling, magic-angle graphene becomes a powerful ferromagnet.
It's rare for magnetism and superconductivity to appear in the same material platform, according to the senior author of the research. We've shown that we can create magnetism in a system that hosts superconductivity. This gives us a new way to study magnetism and superconductivity, and provides exciting new possibilities for quantum science research.
In recent years, magic-angle graphene has caused a stir in physics. Graphene is a two-dimensional material made of carbon atoms. The material strength and electrical conductance of single sheets of Graphene are very interesting. Graphene sheets are stacked. The electrons in a sheet of Graphene interact with those in another sheet. Changing the angle of the sheets with respect to each other can lead to interesting quantum phenomena.
This new research adds a new twist to the system. The state of electron behavior in certain materials in which each electron's spin is linked to its atomic nucleus is called spin-orbit coupling.
The study's lead author Jiang-Xiazi Lin said that spin-orbitcoupling gives rise to a wide range of interesting quantum phenomena, but it's not normally present in magic-angle graphene. We wanted to see what effect spin-orbitcoupling had on the system.
Li and his team interfaced magic-angle graphene with a block of tungsten diselenide, a material that has strong spin-orbit coupling. Aligning the stack causes spin-orbit coupling. The team probed the system with external electrical currents and magnetic fields.
Experiments show that an electric current flowing in one direction across the material in the presence of an external magnetic field produces a voltage in the direction that the current is travelling. The Hall effect is a telltale sign of an magnetic field in the material.
The research team was surprised that an external magnetic field could be used to control the magnetic state. Magnetic materials without spin-orbit coupling can't be controlled because the magnetism can't be controlled by the external magnetic field.
"This observation is an indication that spin-orbitcoupling is present and provided the clue for building a theoretical model to understand the influence of the atomic interface," said Yahui Zhang, a theoretical physicist from Harvard University who worked with the team at Brown to understand the physics associated with the observed magnetism
The influence of spin-orbit is giving scientists a new experimental knob to turn in the effort to understand the behavior of magic-angle graphene, said a Brown graduate student who performed some of the experimental work. The findings have the potential to be used for new device applications.
There is a possible application in the computer. The magnetic properties of magic-angle graphene can be controlled with both external magnetic fields and electric fields. This two-dimensional system is an ideal candidate for a magnetic memory device with flexible read/write options.
The researchers say there is a potential application in quantum computing. The interface between a ferromagnet and a superconductor could be a building block for quantum computers. The problem is that magnets are destructive to superconductivity, so it's hard to create an interface. A material that is capable of both ferromagnetism and superconductivity could be used to create that interface.
Li said that they are working on stabilizing superconductivity and ferromagnetism at the same time. The coexistence of these two phenomena is rare in physics.
Jiang-Xiazi Lin et al., Spin-orbit–driven ferromagnetism at half moiré filling in magic-angle twisted bilayer graphene, Science, is more information. There is a science.abh2889
Science journal information.
There was a magnetic surprise in'magic-angle' graphene on January 6.
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