Many people are aware that in different dimensions, many scientific laws undergo qualitative changes.

For example, gravity, the most universal force in nature, is inversely proportional to the square of the distance in three-dimensional space, inversely proportional to the distance in two-dimensional space, and does not change with distance in one-dimensional space.

Additionally, long-range ferromagnetic order is considered to be allowed in three-dimensional systems, but there is still controversy in the academic community about whether it also exists in two-dimensional systems. (Editor's note: Long-range ferromagnetic order is an important concept in condensed matter physics, describing the arrangement of spins in a material.)

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Since each scientific field may encounter dimensional issues, exploring the scientific laws of fundamental particles in different dimensions is one of the basic scientific issues that is highly concerned and challenging in the academic community.

Combining topological physics research with dimensional issues, and then exploring new topological phenomena in new dimensions, is the research direction that Professor Yuan Xiang of East China Normal University has been focusing on for many years.He developed the steady-state strong magnetic field infrared spectroscopy technology, and through this technology, he systematically studied topological physical phenomena induced by strong magnetic fields in new spatial dimensions, thereby discovering some topological quasi-particles and topological physical phenomena, including one-dimensional Weyl fermions and three-dimensional quantum Hall effects.

With the development of extreme condition strong magnetic field infrared spectroscopy technology, and based on this, the discovery of one-dimensional Weyl fermions and three-dimensional quantum Hall effects, important topological quantum science breakthroughs in new spatial dimensions have been achieved. Yuan Xiang has become one of the Chinese candidates for the "35 Innovators Under 35" in the 2023 MIT Technology Review.

Developing strong magnetic field infrared spectroscopy technology and discovering topological quantum science breakthroughs such as one-dimensional Weyl fermions.

Nowadays, in the process of promoting the progress of our country's science and technology, the independent development of scientific devices is an important part.

Among them, as a continuous strategic research demand, the construction of strong magnetic field large-scale scientific devices has been included in the outline of China's 2035 long-term goals.Although China has reached a world-leading level in magnetic technology, there is still a gap compared to the international level in infrared measurement under steady-state strong magnetic fields.

Based on this background, after joining East China Normal University in 2019, Yuan Xiang began to carry out related instrument innovation with the support of the school and relevant funds.

It took about three years for him to lead the team to overcome the difficulties of infrared compatibility, propose and implement an external detection scheme, and independently develop strong magnetic field infrared spectroscopy technology.

It is also this breakthrough that has laid the main technical foundation for Yuan Xiang to achieve the following scientific results.

Chirality is a basic concept in various scientific fields such as chemistry and physics.The human left and right hands are a typical example of "chirality," which cannot be completely superimposed by any rotation or flipping, but can only be mirror images of each other.

In addition, Weyl fermions are also an example of chirality.

They have novel characteristics such as chiral anomaly and open Fermi arc, which have been discovered in material systems represented by tantalum arsenide (TaAs) and have been extensively studied in three dimensions.

In principle, chiral fermions can be produced in any odd dimension, but most of the current research has only reported three-dimensional Weyl fermions, while textbooks always start with one-dimensional Weyl fermions when introducing them, and then generalize to the three-dimensional case.

"This indicates that we can not only obtain three-dimensional Weyl fermions, but also one-dimensional Weyl fermions. Moreover, from a mathematical point of view, one-dimensional Weyl fermions are the most basic form," said Yuan Xiang.By utilizing the aforementioned high magnetic field infrared spectroscopy technique, he observed the optical transition activity between Landau levels under high magnetic field conditions and found that the topological insulator underwent three topological phase transitions in succession.

Xiang Yuan said: "Due to the unique band inversion of the topological insulator and the characteristic of zero-level Landau level spin polarization, its zero-level Landau band crosses under high magnetic field, simultaneously causing a topological Lifshitz phase transition."

This allowed Xiang Yuan and his collaborators to not only discover one-dimensional Weyl fermions but also to realize the lowest-dimensional Weyl fermions and verify the differences between one-dimensional and three-dimensional Weyl fermions [1].

"As we expected, the laws of physics often undergo qualitative changes in different dimensions. We found that the photoconductivity of one-dimensional Weyl fermions is extremely high in the far-infrared, while that of ordinary three-dimensional Weyl fermions is zero," said Xiang Yuan.

Additionally, it is worth mentioning that the study was praised by Professor Julong from the Massachusetts Institute of Technology as a "significant advancement in the field of quantum materials" [2].In fact, during the course of this research, they encountered many technical and scientific challenges.

Technically speaking, due to the small size of the objects being studied and the relatively long wavelength of infrared spectroscopy, they spent a lot of time and effort to make the research objects as large as possible.

From a scientific perspective, they found that the data collected through experiments could not completely correspond with the theory in many details.

"Trying to understand the parts of the experimental data that are different from the existing theory is the main difficulty we face. But the facts also prove that it is often these experimental phenomena that have important scientific significance," said Yuan Xiang.

The three-dimensional quantum Hall effect is a topological physical phenomenon that he discovered together with his collaborators during his doctoral studies.The quantum Hall effect, as a key scientific discovery in the field of condensed matter physics from the last century to the present, was theoretically considered to only exist in two-dimensional systems.

However, the two open Fermi arc surface states of Weyl semimetals will couple through the chiral zero-energy level of the bulk to form a closed three-dimensional electron cyclotron orbit, namely the Weyl orbit.

Based on this theoretical mechanism, Yuan Xiang and his team provided experimental evidence for the three-dimensional quantum Hall effect under strong magnetic fields, updating the understanding that the quantum Hall effect can only exist in two-dimensional systems [3].

Even the most fundamental scientific research may benefit humanity in the distant future.

As a native of Shanghai, Yuan Xiang's main growth experience is in Shanghai."I completed my secondary education at Shanghai Civilian Middle School and Shixi Middle School, and obtained my bachelor's, master's, and doctoral degrees at Fudan University. After obtaining my doctorate, I have been a professor at East China Normal University to this day," said Yuan Xiang when talking about his growth background and educational experience.

For him, engaging in scientific research is both a childhood dream and a lifelong pursuit.

During his graduate studies, he was engaged in the research of two-dimensional physics and molecular beam epitaxy technology for a considerable period of time, and then his interest turned to the study of topological quantum states under extreme conditions of strong magnetic fields.

After joining East China Normal University, he mainly focused on topological states in new dimensions and made a series of scientific discoveries represented by the aforementioned research results.

It is worth noting that not long ago, he also discovered the three-dimensional Van Hove singularity [4] using a strong magnetic field.Previously, the Van Hove singularity was thought to exist only in one and two dimensions, but Yuan Xiang led his team to discover a three-dimensional Van Hove singularity in a magnetic topological system.

"The Van Hove singularity is a point of infinite density of electronic states in a solid, which means that there are a lot of electronic states allowed near that point, and there will be a strong interaction between the electrons and the external field as well as among themselves," Yuan Xiang explained.

Since we live in a three-dimensional world, if the Van Hove singularity can be realized in three dimensions, it may be found in more systems and help the research on this physical characteristic.

Overall, the key significance of this achievement is mainly reflected in the following two aspects.

Firstly, the correlation between the Van Hove singularity electrons and electrons is relatively strong, so this achievement can provide researchers in related fields with a new method for studying correlated physics.Secondly, due to the strong interaction between the Van 't Hoff singularity electrons and the external field, this achievement is expected to promote the application in the field of sensitive sensing in the future.

It is obvious that the research engaged by Yuan Xiang belongs to very basic science, and he can naturally be defined as an academician.

Based on the situation of his discovery being transformed into applications, it may not happen, or it may happen in the distant future.

In this case, how does he view the impact of his research on the whole society and even the whole world?

"At that time, when Einstein proposed the theory of relativity, on the one hand, people were unwilling to believe it, and on the other hand, they did not think it had anything to do with our lives. But looking at it from today, without the theory of relativity, there would be no indispensable global positioning system technology in modern society." Yuan Xiang said.He believes that although the scientific research he has conducted is fundamental, he also looks forward to it having the opportunity to benefit humanity in the future. Even if they cannot be transformed into applications at present, some of them may play an important application value in the future.

"From a personal perspective, no matter whether the research I have done will directly contribute to the development of society in the future, even if it only helps to eliminate some wrong options, as long as I am in this scientific community, then I have made my own contribution," said Yuan Xiang.

At present, he is still studying the laws of science in new dimensions, including topological physics, unconventional superconductivity, and some novel physical properties.

In addition, he also hopes to extend the strong magnetic field infrared spectroscopy technology to micro-areas, so that the experimental foundation can be expanded to nanomaterials and nanostructures.

"This century is the century of nanotechnology. The more we can understand the structure at a small scale, the more it is conducive to exploring the physical properties at the macro level," said Yuan Xiang.Operations/Layout: He Chenlong