This discovery has the potential to pave the way for smaller, faster electronic devices.
In the world of particles, two can be better than one. For example, consider an electron pair. The combination of two electrons allows the material to slide without friction and give the material special superconducting properties. Such a pair of electrons, or Cooper pair, is a kind of hybrid particle. In other words, it is a complex of two particles that behaves as one particle and has properties that are greater than the sum of its parts.
now MIT Physicists have detected another type of hybrid particle in anomalous two-dimensional magnetic materials. They determined that hybrid particles were a mashup of electrons and phonons (quasiparticles produced from the vibrating atoms of a material). When they measured the force between the electron and the phonon, they found that the adhesive, or bond, was 10 times stronger than any other electron-phonon hybrid ever known.
The extraordinary bonds of the particles suggest that their electrons and phonons may be tandemly tuned. For example, a change to an electron should affect phonons and vice versa. As a rule, electronic excitations such as voltage and light applied to hybrid particles can stimulate electrons as usual, affect phonons, and affect the structural or magnetic properties of the material. This dual control allows scientists to apply voltage or light to a material to adjust its electrical properties as well as its magnetism.
The results are particularly relevant as the team identified hybrid particles of nickel phosphorus trisulfide (NiPS).3), A two-dimensional material that has recently attracted attention due to its magnetic properties. For example, if these properties could be manipulated through newly detected hybrid particles, scientists could one day make a new kind of magnetism that could make this material smaller, faster, and more energy-efficient. I believe it will be useful as a semiconductor.
“Imagine being able to stimulate electrons and react with magnetism,” says Nuh Gedik, a professor of physics at MIT. “That way, the device can be very different from what it is today.”
Gedik and his colleagues published the results in the journal on January 10, 2022. Nature Communications.. His co-authors include Emre Ergeçen, Batyr Ilyas, Dan Mao, Hoi Chun Po, Mehmet Burak Yilmaz, Senthil Todadri from MIT, and Junghyun Kim and Je-Geun Park from Seoul National University in South Korea.
The field of modern condensed matter physics is partly focused on exploring the interactions of matter on a nanoscale. Such interactions between the material’s atoms, electrons, and other subatomic particles can lead to surprising results such as superconductivity and other exotic phenomena. Physicists look for these interactions by condensing chemicals on the surface and synthesizing a sheet of two-dimensional material that can be as thin as a single atomic layer.
In 2018, a South Korean research group discovered an unexpected interaction with a synthetic sheet of NiPS.3, About 150 Kelvin, a two-dimensional material that becomes antiferromagnetic at very low temperatures of -123 degrees Celsius.. The microstructure of an antiferromagnetic material resembles a honeycomb lattice of atoms, the spin of which is opposite to that of adjacent atoms. Ferromagnets, in contrast, are composed of atoms with spins aligned in the same direction.
NiPS Probing3The group found that exotic excitations became visible when the material was cooled below the antiferromagnetic transition, but the exact nature of the interactions responsible for this was unknown. Another group discovered signs of hybrid particles, but the relationship between their exact components and this exotic excitation was also unclear.
Gedik and his colleagues wondered if ultrafast lasers could capture characteristic movements to detect hybrid particles and extract the two particles that make up the whole.
Normally, even with the fastest cameras in the world, the movement of electrons and other subatomic particles is too fast to image. According to Gedik, this task is similar to taking a picture of a running person. The resulting image is blurry because the shutter speed of the camera that captures the light and captures the image is not fast enough and the person is running in the frame before the shutter takes a clear image.
To avoid this problem, the team used an ultrafast laser that emits an optical pulse that lasts only 25 femtoseconds (1 femtosecond is one millionth of a billionth of a second).They split the laser pulse into two separate pulses and directed them at the NiPS sample.3.. The two pulses were set with a slight delay from each other so that the first pulse stimulated or “kicked” the sample and the second pulse captured the sample response with a time resolution of 25 femtoseconds. In this way, they were able to create an ultra-fast “movie” that could infer the interactions of different particles in the material.
In particular, they measured the exact amount of light reflected from the sample as a function of time between the two pulses. In the presence of hybrid particles, this reflection should change in a particular way. This was found to be the case when the sample was cooled to less than 150 Kelvin when the material became antiferromagnetic.
“We found that this hybrid particle only appears below certain temperatures when magnetism is on,” says Ergeçen.
To identify a particular component of a particle, the team changes the color or frequency of the first laser, around a particular type of transition known to occur when the frequency of the reflected light is an electron. At one point I discovered that hybrid particles are visible and move between two d-orbitals. They also examined the intervals of the periodic patterns visible in the reflected light spectrum and found that they matched the energy of certain types of phonons. This reveals that the hybrid particle is composed of excited d-orbital electrons and this particular phonon.
They further modeled based on the measurements and found that the force that binds the electron to the phonon is about 10 times stronger than the force estimated by other known electron-phonon hybrids.
“One potential way to take advantage of this hybrid particle is to bind it to one of the components and allow the other to be indirectly tuned,” says Ilyas. “This allows you to change the properties of the material, such as the magnetic state of the system.”
Reference: “Magnetic brightened dark electron-phonon bound state in van der Waals antiferromagnetism” Emre Ergeçen, Batyr Ilyas, Dan Mao, Hoi Chun Po, Mehmet Burak Yilmaz, Junghyun Kim, Je-Geun Park, T. Senthil, Nuh Gedik, January 10, 2022, Nature Communications..
DOI: 10.1038 / s41467-021-27741-3
This study was partially supported by the US Department of Energy and the Gordon and Betty Moore Foundation.