Recently, the dazzling physics journal named “Physical Review Letters” or shortly known as (PRL) published a solid research from our Physics Department 2017 junior graduated Lu Qiangsheng as the first author with the assistance from our school physics post-doctoral Wu Minghui and Wu Di who is our research assistant professor a paper entitled “Unexpected large hole effective masses in SnSe revealed by angle resolved photoemission spectroscopy”

This research is assembled thanks to the cooperation with our University department of Physics and the Material Science and Engineering of Beijing University. The experimental ARPES was completed by department of Physics graduate Lu Qiangsheng and his academic mentor Liu Chang, the first principle calculation of tin on selenium band was completed by department of Physics postdoctoral Wu Minghui and co supervisor Huang Li, the calculation of transport model was completed by Assistant Professor in the department of Physics Wu Di and co supervisor He Jiaqing, the physical properties of tin selenide system is explained from the increase of the effective mass. He Jiaqing proposed and designed the overall project while Huang Li and Liu Chang are the authors of the paper.

Left: ARPES experimental data for SnSe.
Right: the first principle of SnSe energy band calculation

Based on the ARPES data on this paper, the electrical parameter from the transport model is compared with the experimental one.

Thermoelectric materials are able to achieve direct conversions of heat from new energy material efficiently, with low toxicity and lower costs, which is the reason why the large scale commercial implementation is needed and researchers are focusing on its development and utilization. Studies have found in recent years that SnSe maintains the world record of the highest quality factor carrying (ZT) in the thermoelectric materials by its excellent properties mainly from the ultra high power factor and its low rate of lattice thermal conductivity, however, there is no solid evidence, so the Angle Resolved Photoelectron Spectroscopy (ARPES) is currently the best method not to only study its properties but also to find the solid evidence we are all looking for because of its high end instrument that can directly measure the band structure of single crystal samples.

In this paper, Lu Qiangsheng makes use of the ARPES instrument of our University to meticulously measure the band structure of the SnSe single crystal at different temperatures varying from 80-600 K. According to the results of the analysis, it seems that the effective mass of the holes in the system is larger than the theoretical value, and the lower the temperature the greater the effective mass. From this hypothesis combined with the single-band transport model, they found that the abnormal increase in the effective mass can quantitatively explain the electrical properties at the measured temperature. Therefore, the paper provides a new explanation of the electrical behavior on thermoelectric materials.

It is worth to recall that all ARPES results on this paper were done under the guidance of Professor Liu Chang due measurements at high temperature is uncommon in the industry. Lu Qiangsheng proved his powerful instruments operation ability.

Lu Qiangsheng is an undergraduate student from our department of physics, he has been studying at the University of Missouri in the United States from 2013 to July this year. The experiment in this article was completed by the end of 2016, where he showed and proved how qualified he is. He also led a team of graduate and doctoral candidates to successfully debut a laser ARPES instrument purchased by Nanjing University, which has been well received by its professors and student.

Official report linked here: http://www.sustc.edu.cn/news_events_/3663
Translation and Layout Design by Semson J Nip

Abstract link: https://journals.aps.org/prl/accepted/26074Y88P0417f6a99fd2a453275fe5ea0438760c