Stacking order and driving forces in the layered charge density wave phase of 1T-MX2 (M = Nb, Ta and X = S, Se)

Abstract

The group-V transition metal dichalcogenides (TMD) have attracted a lot of research due to their unique structures and rich physical properties. In these materials, charge density waves (CDW) are still the subject worthy of in-depth research despite being a popular issue. Based on first principles, the stacking effect of the T- MX2 (M = Nb, Ta and X = S, Se) CDW phase are comprehensively explored, with the interplay of correlation effect and magnetic order. Without correlation effect, T- MX2 with one specific stacking order (AA_AC_AA) is most structurally stable and leads to a natural band insulator due to interlayer dimerization. In contrast, same materials with the other stacking orders (AA_AB_AA, AA, AB, AC) are metallic phase. In the presence of correlation effect, whether the systems are insulators or metal highly depends on the magnetic order. AA_AC_AA stacking T- MX2 with antiferromagnetic order end up with band insulator. T- MX2 with AA, AB, AC stacking are metal even in the presence of correlation effect, but with magnetic order, they become Mott insulator. The complication is that AA_AB_AA stacking is located at the intersection of the band insulator and Mott insulator. From this article, we can see T-MX2 with different stacking structure with/without correlation effect and magnetic order show different phases. We outline a rich landscape and systematically explain the causes of the insulating characteristic of the CDW phase and emphasizes the critical role of correlation effect and magnetic order, extending the underlying mechanism of metal-insulation transitions that previously relied only on Mott localization as a driving force.