News FY 2022

OUJ Delegates Participated in the 80th Anniversary Conference of National University of Mongolia (NUM)

From October 4th to 6th, 2022, the OUJ delegation consisting of Prof. Tsuneo Yamada, Advisor to the OUJ President and Chair of the International Exchange Committee, Prof. Yumiko Nara, and Ms. Mai Tanaka, Deputy Head of General Affairs Division, participated in the 80th anniversary celebration conference of NUM.

Entrance to the Campus of NUM

NUM was established in 1942 as the first institution of higher education in Mongolia. It has made contributions to the foundation of the higher education system in Mongolia by establishing six colleges. In recent years, the university has also been promoting distance education.
OUJ and NUM signed a memorandum of understanding (MOU) in October 2019 on cooperation in joint research, exchange of faculty and staff, and collaborative development and sharing of teaching materials.

Ceremony at the Parliament House

The ceremony was held on October 5th at the Parliament House in Ulaanbaatar, Mongolia, in the presence of the university's faculty, staff, alumni, and administrators and representatives of international institutions.
Cooperative and international partners participated in the anniversary conference and commemorative activities of NUM and took part in a wide-range program to understand the history, traditions, and cultural heritage of Mongolia.

We expect both universities will continue to cooperate and engage in further active exchanges and evolve with each other.

With President Dr. Bayanjargalyn Ochirkhuyag (fourth from left),
Prof. Tsuneo Yamada (third from left), Prof. Yumiko Nara (fourth from right), Ms. Mai Tanaka (third from right)

PRESS RELEASE

Source: Tokyo Institute of Technology, The Open University of Japan, Osaka Metropolitan University

November 18, 2022

Truly Chiral Phonons Observed in Three-Dimensional Materials for the First Time

Chirality can be true or false, depending on the symmetry of dynamic propagation. Crystal lattice vibrations, called phonons, can also display chirality as has been shown in some two-dimensional structures. However, truly chiral phonons have never been observed in three-dimensional systems—that is, until now. Researchers from Tokyo Tech have identified these for the first time, in bulk cinnabar. Utilizing pseudo-angular momentum, their method can be used to identify the chirality in crystalline structures.

Chirality is the breaking of reflection and inversion symmetries. Simply put, it is when an object’s mirror images cannot be superimposed over each other. A common example are your two hands—while mirror images of each other, they can never overlap. Chirality appears at all levels in nature and is ubiquitous. In addition to static chirality, chirality can also occur due to dynamic motion including rotation. With this in mind, we can distinguish true and false chirality. A system is truly chiral if, when translating, space inversion does not equate to time reversal combined with a proper spatial rotation.

Phonons are quanta (or small packets) of energy associated with the vibration of atoms in a crystal lattice. Recently, phonons with chiral properties have been theorized and experimentally discovered in two-dimensional (2D) materials such as tungsten diselenide. The discovered chiral phonons are rotating—yet not propagating—atomic motions. But, truly chiral phonons would be atomic motions that are both rotating and propagating, and these have never been observed in three-dimensional (3D) bulk systems.

Now, a team of researchers led by scientists from Tokyo Institute of Technology (Tokyo Tech) have identified truly chiral phonons, both theoretically and experimentally. The team, led by Professor Takuya Satoh of the Department of Physics at Tokyo Tech, observed the chiral phonons in cinnabar (α-HgS). This was achieved using a combination of first-principles calculations and an experimental technique called circularly polarized Raman scattering. “Chiral structures can be probed using chiral techniques. So, using circularly polarized light, which has its own handedness (i.e., right-handed or left-handedness), is critical. Dynamic chiral structures can be mapped using pseudo-angular momentum (PAM). Pseudo-momentum and PAM originate from the phase factors acquired by discrete translation and rotation symmetry operations, respectively,” explains Professor Satoh.

The researchers’ novel experimental approach also allowed them to probe the fundamental traits of PAM. They found that the law of the conservation of PAM—one of the key laws ofphysics—holds between circularly polarized photons and chiral phonons. “Our work also provides an optical method to identify the handedness of chiral materials using PAM. Namely, we can determine the handedness of materials with better resolution than x-ray diffraction (XRD) can achieve. Moreover, XRD requires a large-enough crystal, is invasive, and can be destructive. Circularly polarized Raman scattering, on the other hand, allowed us to determine the chirality of structures XRD could not, in a non-contact and non-destructive manner,” concludes Professor Satoh.

This study is the first to identify truly chiral phonons in 3D materials, which are clearly distinct from those seen previously in 2D hexagonal systems. The learnings gained here could drive new research into developing ways for transferring the PAM from photons to electron spins via propagating chiral phonons in future devices. Furthermore, this approach enables the determination of the true chirality of a crystal in an improved manner, providing a new critical tool for experimentalists’ and researchers.

Reference

Authors:
Kyosuke Ishito1, Huiling Mao1, Yusuke Kousaka2,3, Yoshihiko Togawa2, Satoshi Iwasaki3, Tiantian Zhang1,4, Shuichi Murakami1,4, Jun-ichiro Kishine5,6 and Takuya Satoh1

Title of original paper:
Truly chiral phonons in α-HgS

Journal:
Nature Physics

DOI:
10.1038/s41567-022-01790-x

Affiliations:

  1. Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
  2. Department of Physics and Electronics, Osaka Metropolitan University, Osaka, Japan
  3. Research Institute for Interdisciplinary Science, Okayama University, Okayama, Japan
  4. Tokodai Institute for Element Strategy (TIES), Tokyo Institute of Technology, Tokyo, Japan
  5. Division of Natural and Environmental Sciences, The Open University of Japan, Chiba, Japan
  6. Institute for Molecular Science, Okazaki, Japan

*Corresponding author’s email: satoh@phys.titech.ac.jp

Contact

Kazuhide Hasegawa
Public Relations Division,
Tokyo Institute of Technology
media@jim.titech.ac.jp
+81-3-5734-2975

Truly chiral phonons—i.e., rotating and propagating atomic motions seen in a crystal lattice—have never been observed in a bulk 3D material. However, now, Tokyo Tech researchers have identified these in cinnabar.