[论文解读] Charge Density Wave Order and Superconductivity in Janus MoXH Monolayers

J. Seeyangnok, U. Pinsook+1 more|arXiv (Cornell University)|Jan 6, 2026

2D Materials and Applications被引用 1

一句话总结

本论文表明，Janus MoXH 单层在 M 点软声子驱动下具有固有的可整律CDW基态，并考察CDW如何与超导耦合以及可通过应变、掺杂和温度调控。

ABSTRACT

Two-dimensional Janus hydrogenated transition metal chalcogenides provide an unusual platform where lattice instabilities, electron-phonon coupling, and superconductivity are strongly intertwined. Using first-principles calculations, we demonstrate that Janus 2H and 1T MoXH (X = S, Se) monolayers host an intrinsic, commensurate charge density wave (CDW) ground state originating from soft phonon modes at the Brillouin zone M point. Real-space supercell optimizations confirm that the CDW reconstruction lowers the total energy and fully stabilizes the lattice, eliminating the imaginary phonon modes present in the high-symmetry metallic structures. Analysis of the electronic susceptibility shows that the CDW instability is not driven by Fermi surface nesting, but instead arises from strong electron-phonon coupling. We further reveal a material-dependent interplay between CDW order and superconductivity. In 1T MoSH, CDW formation enhances low-energy phonon contributions and strengthens electron-phonon coupling, leading to an increased superconducting transition temperature. In contrast, for 1T MoSeH and 2H MoSeH, the CDW phase suppresses electron-phonon coupling and reduces superconductivity. Finally, we show that thermal fluctuations, compressive strain, and carrier doping can selectively suppress CDW order and restore superconductivity. These results establish Janus MoXH monolayers as a tunable two-dimensional system for exploring lattice-driven charge ordering and its competition with superconductivity.

研究动机与目标

• 研究Janus MoXH单层（X = S, Se）的晶格不稳定性及可能的CDW形成。
• 确定CDW是由费米面EL 尺 nesting还是电子–声子耦合驱动。
• 评估CDW序对电子–声子耦合以及超导性Tc的影响。
• 探索外场控制参数（应变、掺杂、温度）以操控CDW与超导性。

提出的方法

• 计算高对称性Janus MoXH结构的声子色散并识别M点的软模。
• 进行Real-space 2x2 CDW超胞弛豫以確認可整律CDW基态。
• 分析电子易化率（Re[χ0]、Im[χ0]）和声子线宽以区分 nesting 与电子–声子耦合效应。
• 将CDW基态与经应变/掺杂的高对称结构进行比较，以评估电子–声子耦合和Tc的变化。
• 使用从头分子动力学评估CDW在有限温度下的稳定性（约50 K）。
• 考察轨道分辨的电子结构，以理解两相中费米能级附近的带结构。

Figure 1: Phonon dispersions and lattice instabilities in hydrogenated Mo-based monolayers. a–c , Phonon dispersion relations of (a) 1T–MoSH, (b) 2H–MoSeH, and (c) 1T–MoSeH calculated for the high-symmetry structure (HSS, red lines) and the CDW phase (blue lines) along the high-symmetry path $\Gamma

实验结果

研究问题

• RQ1 观察到的Janus MoXH单层CDW是由费米面 nesting 还是动量相关的电子–声子耦合驱动？
• RQ2 CDW形成如何影响不同MoXH同晶型中的电子–声子耦合及超导Tc？
• RQ3 应变、掺杂或温度是否能抑制CDW并恢复或增强超导性？
• RQ4 在S与Se变体的2x2超胞中，CDW基态的性质与稳定性为何？
• RQ5 CDW序如何重塑电子结构与这些材料中的EPC热点？

主要发现

• CDW序是固有且可整律的，来自于1T–MoSH、1T–MoSeH和2H–MoSeH中M点的软声子。
• CDW不稳定性由强的动量相关电子–声子耦合驱动，而非费米面 nesting。
• 结构弛豫得到一个稳定的2x2 CDW相，无虚部声子，替代高对称的金属性结构。
• 在1T–MoSH中，CDW增强低能声子贡献并加强电子–声子耦合，提升Tc。
• 在1T–MoSeH与2H–MoSeH中，CDW抑制电子–声子耦合并降低Tc。
• CDW可被热涨落、压缩应变或载流子掺杂所抑制，但抑制行为因材料而异（尤其在1T–MoSeH中未完全可抑制）。
• 在研究的体系中，超导性始终在既有CDW背景下出现（Tc < TCDW）。

Figure 2: Interplay between phonon softening and electronic susceptibility in Janus MoXH monolayers. Rows correspond to ( a ) 1T–MoSH, ( b ) 1T–MoSeH, and ( c ) 2H–MoSeH. Left panels show the momentum-dependent phonon linewidth $\gamma(\mathbf{q},\nu{=}1)$ of the lowest-energy (ZA) phonon mode along