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MIT physicists discover strange hybrid particles bound together by 'glue' of unique density

MIT physicists discover strange hybrid particles bound together by ‘glue’ of unique density

This discovery could provide a path to smaller and faster electronic devices.

In the particle world, sometimes two is better than one. Take, for example, electron pairs. When two electrons are bonded together, they can slide through the material without friction, giving the material superconducting properties. These electron pairs, or Cooper pairs, are a type of hybrid particle — a compound of two particles that behave as one, with properties greater than the sum of its parts.

right Now with Physicists have discovered another type of hybrid particle in an unusual two-dimensional magnetic material. They determined that a hybrid particle is a mixture of an electron and a phonon (a quasi-particle produced from the vibrating atoms of matter). When they measured the force between the electron and the phonon, they found that the gum, or bond, is 10 times stronger than any other electron-phonon hybrid known to date.

The particle’s exceptional bonding indicates that the electron and phonon can be tuned side by side; For example, any change in the electron must affect the phonon and vice versa. In principle, electronic excitation, such as a voltage or light, applied to a hybrid particle can excite the electron as it normally would, and also affect the phonon, affecting the structural or magnetic properties of the material. Such dual control could allow scientists to apply voltage or light to a material to adjust not only its electrical properties, but also its magnetism.

Artist’s impression of electrons in orbitals interacting strongly with the lattice’s vibrational waves (phonons). The lobular structure represents the electronic cloud of nickel ions in NiPS3, also known as orbitals. The waves emitted by the orbital structure represent the oscillations of the phonons. The glowing bands indicate the formation of a correlated state between the electrons and the lattice vibrations. Credit: Emre Ergecin

Particularly relevant were the results, as the team identified a nickel-phosphorous trisulfide (NiPS) hybrid particle.3), a two-dimensional material that has sparked recent interest in its magnetic properties. If these properties can be manipulated, for example through newly discovered hybrid particles, scientists believe the material could one day be useful as a new type of magnetic semiconductor, which can be made into smaller, faster, more energy-efficient electronics. .

“Imagine if we could excite an electron and make the magnetism interact,” says Noh Gedek, professor of physics at MIT. “Then you can create devices that are completely different from how they work today. “

Jedek and colleagues published their results on January 10, 2022 in the journal Connecting with nature. Co-authors include Emre Ergesen, Patir Elias, Dan Mao, Hui Chun-bo, Mehmet Burak Yilmaz and Senthil Todadri of MIT, as well as Junghyun Kim and Je-Geun Park at Seoul National University in Korea.

particle sheets

The field of modern condensed matter physics is focused, in part, on researching interactions in matter at the nanoscale. Such interactions between atoms of a substance, electrons and other subatomic particles can lead to surprising results, such as superconductivity and other strange phenomena. Physicists investigate these interactions by condensing chemicals on surfaces to form sheets of two-dimensional materials, which can be as thin as the atomic layer.

In 2018, a research group in Korea discovered unexpected interactions in NiPS composite sheets3, a two-dimensional material that becomes antimagnetic at very low temperatures of 150 K, or -123 degrees Celsius. The microscopic structure of ferromagnetism resembles a honeycomb network of atoms whose rotation is opposite to that of their neighbours. In contrast, a magnetic material consists of atoms whose spins align in the same direction.

Via NiPS . assay3, this group found that the strange excitation becomes visible when the material is cooled below its antimagnetic transition, although the exact nature of the interactions responsible for this is unclear. Another group found signs of a hybrid particle, but its exact components and relationship to this strange excitation were not clear either.

Gidick and his colleagues wondered if they could detect the hybrid particle, reveal the two particles that make up the ensemble, and capture their signature motions with an ultrafast laser.

magnetically visible

The movement of electrons and other subatomic particles is usually very fast to photograph, even with the world’s fastest camera. The challenge is like taking a picture of someone running, says Gedek. The resulting image is blurry because the shutter, which allows the light to capture the image, is not fast enough and the person is still working in the frame before the shutter can take a sharp picture.

To get around this problem, the team used an ultrafast laser that emits pulses of light lasting just 25 femtoseconds (one femtosecond is a millionth of a billionth of a second). They split the laser pulse into two separate pulses and direct them to a NiPS . sample3. The two pulses are set with a slight delay from each other so that the first stimulates or “kicks” the sample, and the second captures the sample’s response. , with a time precision of 25 femtoseconds. In this way, they were able to create ultra-fast “movies” from which the interactions of various particles within matter could be inferred.

In particular, they measured the exact amount of light reflected from the sample as a function of the time between the two pulses. This inversion must somehow change in the case of hybrid molecules. This has been found to be the case when the sample is cooled below 150 K, when the material becomes antimagnetic.

“We discovered that this hybrid particle was only visible below a certain temperature, when magnetism is activated,” explains Ergeçen.

To determine the specific components of the particle, the team changed the color or frequency of the first laser and found that the hybrid particle was visible when the frequency of the reflected light was around a specific type of transition. The electron moves between two orbits d. They also looked at the divergence of the visible periodic pattern in the reflected light spectrum and found that it corresponded to the energy of a particular type of phonon. This showed that the hybrid particle consists of the excitation of a d orbital electron and this specific phonon.

They did further modeling based on their measurements and found that the force binding the electron to the phonon is about 10 times stronger than what has been estimated for other known electron-phonon hybrids.

“One potential way to harness this hybrid particle is that it could allow you to pair with one component and indirectly tune the other,” Elias said. “This way you can change the properties of a material, such as the magnetic state of the system.”

Reference: “Magnetically Illuminated Dark Electron and Phonon States in a Van der Waals Magnetic Inhibitor” by Emre Ergesen, Pater Elias, Dan Mao, Hui Chun-bo, Mehmet Burak Yilmaz, Jonghyun Kim, Jeon Park, T. Senthel, and Noh Gedik, Jan. 10, 2022, Available here. Connecting with nature.
DOI: 10.1038 / s41467-021-27741-3

This research was funded in part by the US Department of Energy and the Gordon and Betty Moore Foundation.

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