Figure 1. In the low temperature phase, every 13 Ta atoms shrink to form a 'David' cluster of stars. The red arrow marks the direction of shrinkage.
Figure 2. (a) In-plane and (b) schematic diagram of orbital densities. Each yellow hexagonal star represents a 'David' star cluster, and red, green and blue correspond to the Ta-5d3z2-r2 orbit.
Recently, Zou Liangjian, a researcher at the Institute of Solid State Physics, Chinese Academy of Sciences, co-operated with researcher Lin Haiqing and Chang Kai from Beijing Computational Center. Through the research on the bulk materials, monolayers System, high temperature normal phase and low temperature charge density wave phase, we find that electron correlation and orbital density wave play an important role in the formation of low temperature phase.The related research results were published in "Physical Review B".
Experimental results show that 1T-TaS2 has a rich phase transformation process, and as the temperature decreases, it undergoes a third-order phase transition of impure charge density wave, quasi-common charge density wave and common degree charge density wave. In the last phase After the change, the system will change from metal to insulator.This material has been studied for many years, but its low-temperature phase transition mechanism is not yet conclusive.
In order to explore the low-temperature phase transition mechanism of 1T-TaS2, the researchers used the density functional theory and the kinetic mean field theory to systematically study the 1T-TaS2, a two-dimensional charge density wave material.Firstly, Each 13 Ta atoms shrink at low temperature to form a 'David' cluster (Figure 1). By analyzing the orbital characteristics near the Fermi level, we find that there is orbital density in the system, mainly due to Ta- 5d3z2-r2 contribution (Figure 2). Combined with the kinetic mean field theory results, the researchers further determined that under the combined effects of structural distortion and Coulomb correlation makes the low temperature charge density wave insulation phase stable, and then observed experimentally; At the same time, orbital density wave plays an important role.In addition, the researchers found that the ground state of the bulk system is an interlayer antiferromagnetic state, the ground state of the single-layer system is a ferromagnetic state.This study provides a follow-up study of the system Important references include orbital mechanisms, exciton physics, flatband features, and potential applications.
The above research has been funded by the National Natural Science Foundation of China.
