Experimental evidence of exciton gas phase and its condensation in two-dimensional materials

Exciton insulators (EI) are macroscopic quantum systems in solids in which electron-hole pairs (excitons) bound by Coulomb interactions undergo Bose-Einstein condensation (BEC). The material realization of exciton insulators is a controversial problem in the scientific community, and the main difficulty is the lack of definitive experimental evidence to distinguish exciton insulators from traditional charge density wave (CDW) states. In the BEC limit of exciton condensation, the unique pre-formed exciton mechanism is an important marker to distinguish EI from traditional CDW, but there is still a lack of direct experimental evidence.

Recently, the team of Tang Shujie from the Institute of Microsystems and Information Technology of the Chinese Academy of Sciences, and the team of Shen Zhixun of Stanford University in the United States cooperated with Sung-Kwan Mo, a professor at Lawrence Berkeley National Laboratory, to achieve the preparation of high-quality monolayer 1T-ZrTe2 films by molecular beam epitaxy (MBE) technology, and revealed experimental evidence for the existence of pre-formed exciton gas phase under the BEC limit by angle-resolved photoelectron spectroscopy (ARPES) and scanning tunneling microscopy (STM). The research results, titled Signatures of the exciton gas phase and its condensation in monolayer 1T-ZrTe2, were published in Nature communications.

In this study, ARPES and STM were used to confirm the presence of 2×2 CDW ground states in a monolayer of 1T-ZrTe2. Furthermore, the study of electron interaction suppression by multiple means of carrier modulation reveals that 1T-ZrTe2 does not directly enter the normal state above the CDW transition temperature Tc, but has an intermediate state with significant correlation. At the same time, the intermediate state exhibits peculiar energy band and energy-dependent folding behavior, which confirms that it is a characteristic of the pre-formed exciton gas phase before the exciton condensation enters the CDW state. The results show that the monolayer 1T-ZrTe2 is an EI candidate with a highly modifiable electronic structure, which provides a two-dimensional platform for exploring the exciton effect. Its layered nature is conducive to the construction of van der Waals heterogeneous structure, and has broad application prospects in the development of exciton effects, such as the use of magnetism to achieve spin superflow.

Figure 1.Temperature evolution of CDW states in epitaxial growth monolayer 1T-ZrTe2

Figure 2. The two-step formation process of CDW states and the exciton effect

Shanghai Microsystem Institute is the first completed unit. The research work has been supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences Strategic Leading Science and Technology Project (Class B), and the Shanghai Daystar Program. (Source: Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences)

Related paper information:

Special statement: This article is reproduced only for the need to disseminate information, and does not mean to represent the views of this website or confirm the authenticity of its content; If other media, websites or individuals reprint and use from this website, they must retain the “source” indicated on this website and bear their own legal responsibilities such as copyright; If the author does not wish to be reprinted or contact the reprint fee, please contact us.

Source link

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button