通过机械稳定的卤素功能化Mo2C MXenes实现增强和可调的超导性
Enhanced and Tunable Superconductivity Enabled by Mechanically Stable Halogen-Functionalized Mo2C MXenes
AI总结：
卤素功能化Mo2C MXenes通过增强电子-声子耦合实现超导性提升，载流子掺杂和应变可调超导性能。
摘要：
我们对卤素功能化Mo2YX2（Y = C, N；X = F, Cl, Br, I）MXene单层的结构、电子、振动和超导性质进行了全面的第一性原理研究。密度泛函理论和密度泛函微扰理论计算表明，在所考虑的卤素化系统中，只有Br-和I-功能化的Mo2C单层是动态稳定的，这通过整个布里渊区内的正定声子光谱得到证实。电子结构计算显示具有金属行为，费米能级附近的状态主要由Mo d轨道主导，具有显著的电子态密度，为强电子-声子耦合（EPC）提供了有利条件。由此得到的EPC常数将两种系统置于强耦合区域，产生超导转变温度为Tc = 13.1 K的Mo2CBr2和Tc = 18.1 K的Mo2CI2，这在Allen-Dynes公式中得到验证。值得注意的是，卤素功能化本身在Mo2C中增强了超导性，Mo2C的Tc为7.2 K，通过增强的电子-声子耦合，其超导转变温度相比原始Mo2C显著提高。此外，我们证明这些系统的超导性通过载流子掺杂和双轴拉伸应变高度可调。电子掺杂显著增强了EPC并提高了Tc，Mo2CBr2的Tc达到21.7 K，Mo2CI2的Tc达到21.3 K。我们的结果将卤素功能化的Mo2C MXenes识别为机械稳定、声子介导的二维超导体，并突显了载流子掺杂作为优化其超导性能的有效策略。
英文摘要：
We present a comprehensive first-principles investigation of the structural, electronic, vibrational, and superconducting properties of halogen-functionalized Mo2YX2 (Y = C, N; X = F, Cl, Br, I) MXene monolayers. Density functional theory and density functional perturbation theory calculations reveal that, among the halogenated systems considered, only Br- and I-functionalized Mo2C monolayers are dynamically stable, as confirmed by positive definite phonon spectra throughout the Brillouin zone. Electronic structure calculations show metallic behavior with states near the Fermi level dominated by Mo d orbitals with pronounced electronic density of states, providing favorable conditions for strong electron-phonon coupling (EPC). The resulting EPC constants place both systems in the strong coupling regime, yielding superconducting transition temperatures of Tc = 13.1 K for Mo2CBr2 and Tc = 18.1 K for Mo2CI2 within the Allen-Dynes formalism. Notably, halogen functionalization itself plays a crucial role in enhancing superconductivity in Mo2C, which has Tc = 7.2 K, leading to a substantial increase in the superconducting transition temperature compared with pristine Mo2C through strengthened electron-phonon coupling. Furthermore, we demonstrate that superconductivity in these systems is highly tunable via carrier doping and biaxial tensile strain. Electron doping significantly enhances EPC and raises Tc up to 21.7 K for Mo2CBr2 and 21.3 K for Mo2CI2. Our results identify halogen-functionalized Mo2C MXenes as mechanically robust, phonon mediated two dimensional superconductors and highlight carrier doping as an effective strategy for optimizing their superconducting performance.
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