CDW and Superconductivity in 4Hb-TaSe2 Heterostructure - Dr. Wenge Yang

Two-dimensional (2D) van der Waals heterostructures (VDWHs) containing a charge-density wave (CDW) and superconductivity (SC) have revealed rich tunability in their properties, which provides a new route for optimizing their novel exotic states. The SC and CDW interaction is critical to their properties, but understanding it within VDWHs is very limited. Now, a new study co-led by HPSTAR scientist Dr. Wenge Yang proposes a novel strategy to regulate the superconductivity and charge-density wave orders in two-dimensional van der Waals heterostructures, revealing their relationship layer-by-layer. “Modulating Charge-Density Wave Order and Superconductivity from Two Alternative Stacked Monolayers in a Bulk 4Hb-TaSe₂ Heterostructure via Pressure” is published in the most recent edition of Nano Letters.

2D VDWHs have attracted great interest in the past decade, particularly for their emergent properties in the transition metal dichalcogenides (TMD) family. Among them, superconductivity and charge-density wave states have been found in many TMD systems with various entangled relationships. However,understanding the interaction between the SC and CDW order in VDWHs remains very limited due to the lack of suitable material systems and proper tuning tools. In contrast, mono-layer TMDS have been investigated extensively to simplify their fundamental physics and finally achieve 2D extreme properties.

Utilizing high pressure and high temperature techniques, Dr. Yang et al. synthesized bulk 4Hb-TaSe₂ single crystals with alternately stacking 1T-TaSe₂ and 1H-TaSe₂ monolayers, thereby doubling the adjacent H-H and T-T layer distance, and largely reducing the third-dimensional coupling to reach quasi-monolayer properties. By combining a suite of in situ high-pressure diagnostic tools and first-principles calculations, the SC, CDW, crystal structure and electronic structure are seen to evolve from both the T- and H-layers under high pressure. Surprisingly, the superconductivity competes with the intralayer and adjacent-layer CDW order in 4Hb-TaSe2, which results in substantially and continually boosted superconductivity under compression. Upon total suppression of the CDW, the superconductivity in the individual layers responds differently to the charge transfer. By revealing this strong competitive relationship between the SC and CDW orders of the intralayer and interlayer coupling, the group established unambiguous phase diagrams of the transition temperatures of SC and charge density wave versus pressure in both the T- and H-layers for the first time.

These results provide an excellent method to efficiently tune the interplay between SC and CDW in VDWHs and a new avenue for designing new materials with tailored properties.

Caption: T_CDW and T_c vs P diagrams of 4Hb-TaSe₂

近日，北京高压科学研究中心杨文革课题组与吉林大学王欣课题组以及南京大学孙建课题组合作，通过对异质结过渡金属二元硫族化合物（TMDs）4Hb-TaSe₂的高压下的研究，发现过渡金属硫化合物的层内以及层间存在显著的电荷密度波与超导的竞争关系。相关结果以“Modulating Charge-Density Wave Order and Superconductivity from Two Alternative Stacked Monolayers in a Bulk 4Hb-TaSe2 Heterostructure via Pressure”为题发表于《纳米快报》。