In 1987, famous physicist and Harvard professor Bertrand Halperin predicted the existence of the three-dimensional quantum Hall effect. After 32 years, Associate Professor Zhang Liyuan from the Department of Physics at Southern University of Science and Technology (SUSTech) collaborated with Professor Qiao Zhenhua of the University of Science and Technology of China (USTC), Professor Yang Shengyuan of Singapore University of Technology and Design (SUTD), Professor Yang Kun of Florida State University (FSU), Professor Patrick A. Lee of Massachusetts Institute of Technology (MIT) and Professor Genda Gu of the Brookhaven National Laboratory, in confirming the prediction of the 3D quantum Hall effect. The research results were recently published in well-known international academic journal Nature.

Dedicated to experimenting

In order to meet this demanding condition, Prof. Zhang’s team deliberately selected the high-quality bulk zirconium pentatelluride (ZrTe5) crystals as the research object. The ZrTe5 crystal is a new three-dimensional topological material with strong anisotropy and layered structure.  It has low carrier density and ultrahigh mobility, which makes it easy to get into the quantum limit regime under the experimental limitation. Additionally, in order to avoid disturbing multiple electronic pockets that would complicate the experiment, the research team deliberately chose samples with single electronic pocket.

The founder of topological order theory and member of the National Academy of Sciences Professor Wen Xiaogang specifically made a comment on their paper. “This new experimental observation has provided a new material system, which can also generate topological order.”

Hard work pays off effort from overcoming difficulties

In the beginning, Prof. Zhang Liyuan’s research group focused mainly on 2D material systems, which is a competitive research field. While conducting this research, Zhang Liyuan noticed the relatively “unpopular” research direction of 3D electron gas and decided to adjust the direction. The experiments first showed a lot of diversity, which brought great confusion to the team.

After persevering and encouraging the team, Prof. Zhang Liyuan recognized a new rule which was neglected previously. The team soon worked together and successfully verified the rule, which proved the existence of the 3D quantum Hall effect. Postdoctoral researcher Wang Peipei said that this experimental breakthrough reflected the long-term perseverance and hardworking of the. He also pointed out that the research group focused on high quality zirconium pentatelluride (ZrTe5) crystals, in order to obtain the best results. “Only when the samples are of enough high quality is it possible to get good experimental results. This is the premise that the research team finally measures the three-dimensional quantum Hall effect.”

Zhang Liyuan said: “Sometimes research is just like mining, make the target, and never give up easily… I can’t propose the impact of this achievement on future academic research and daily life. What I can do is tell everyone that there is a diamond mine beckoning to everyone in this place.”

Rigorous and professional, multi-party cooperation

The research team needed to work with others in order to deeply understand their samples. After testing large amount of samples in the laboratory over the last four years, the first author Tang Fangdong said that it was crucial to understand the data and get its deeper physics. With that in mind, the team keeps working rigorously and efficiently, and received high praise from Prof. Zhang Liyuan.

The importance of interdisciplinary teamwork has become more and more prominent in recent years, just as it does in this work. Research groups from the United States, Singapore and mainland China co-authored this breakthrough paper, providing all kinds of support for this research.

It is also impossible to separate SUSTech’s support for the research. Prof. Zhang Liyuan noted that he had been working on this research since his arrival on campus in 2014, with the full support of SUSTech and the Shenzhen Municipal Government. President Chen Shiyi specifically allocated funds for the research at hard times, and subsequently the project received further support from the Guangdong Provincial Innovation Fund, led by Academician Yu Dapeng. Prof. Zhang Liyuan has seen the rapid rise of Department of Physics and SUSTech during the last five years, and has been deeply moved by the rich academic atmosphere of SUSTech.

Despite all the challenges placed in front of them, the team persisted and finally is able to present their remarkable academic achievement to the world. When asked about the group’s future plans, Prof. Zhang Liyuan said that there are infinite possibilities in the three-dimensional system, as it is more complicating than two-dimensional case, and the group will continue to explore this new research direction. He will keep more patient and passionate to make more excellent academic achievements. He believes that as long as you work hard, the goddess of fortune will bless you.

Paper link: https://www.nature.com/articles/s41586-019-1180-9