博士生谢兴同学在国际权威期刊Physical Review B上发表论文

     近日，课题组成员谢兴同学在刘老师的指导下，以第一作者在国际权威期刊Physical Review B(影响因子4.904)上发表题为 “Unveiling Layer-dependent Interlayer Coupling and Vibrations Properties in MoTe₂ under High Pressure”(DAC高压下MoTe₂的层间耦合和振动特性)的实验论文。

图：DAC高压下MoTe2的层间耦合和振动特性

      层状材料，如石墨烯、黑磷(BP)和过渡金属硫属化物(TMDs)，具有独特的晶体结构，其特点是层间的范德瓦尔斯相互作用。这种独特的结构赋予它们卓越的性质，包括高载流子迁移率、非凡的光电性能和层间带隙，使它们在光电探测器、自旋电子学、谷光电子学和场效应晶体管等各种应用中具有极高的价值。特别是，这种结构特点使得可以通过叠层、扭转角度和外加场等方法灵活调节其性质。目前的研究努力广泛探索了在层状材料及其异质结构中通过高压调节层间耦合来实现的结构转变、半导体-金属转变、光学性质变化和压力诱导超导体。二维(2D)材料的高压研究主要集中在其单层、双层、异质结构和体材料上。目前在不同层数的2D材料上进行系统的高压研究还缺乏。在TMDs中，低频层间振动模式对层数非常敏感，导致了随着厚度增加，切变(S)和呼吸(LB)模式的蓝移和红移。可以使用LCM来描述这些低频S和LB模式，它们的层间行为可以通过风扇图来表征。鉴于S和LB模式与层间相互作用密切相关，通过控制层间耦合，压力可以有效地调节这些模式。然而，在不同厚度的2D材料中，S和LB模式在压力下的响应仍然知之甚少。

     在这项研究中，我们创新地使用金刚石压力对顶砧(DAC)装置进行了单层(1L)到五层(5L)和体材料MoTe₂的高压拉曼光谱研究。得到的高压拉曼光谱显示，S和LB模式的蓝移比率取决于层数，由于层间的恢复力和层间耦合分别呈现截然不同的趋势。此外，我们将LCM扩展到压力领域，并发现随着压力增加，S和LB模式的力常数不断增加。此外，我们揭示了S和LB模式之间以及 A₁/A_1g和 E1/Eg 模式之间的压力诱导强度变化。通过采用键极化模型，我们确定了这种强度变化是由于压力引起的层间Te-Te或层内Mo-Te键的极化分量发生变化所致。我们的研究为理解层间原子振动及其在高压下的响应提供了科学见解。

文章链接：https://link.aps.org/doi/10.1103/PhysRevB.108.155302

Comments:

This paper provides valuable insights into the layer-dependent interlayer coupling and vibrational properties of MoTe₂ under high pressure, shedding light on a crucial aspect of layered materials. Layered materials have become increasingly important due to their tunable physical properties achieved through various mechanisms, including stacking and interlayer coupling. One particularly intriguing aspect of these materials is the sensitivity of their interlayer vibrations to thickness, which can be controlled to manipulate their properties.

The research conducted in this study investigates the behavior of MoTe₂ under high pressure, ranging up to 14 GPa, across different thicknesses, from monolayer to bulk. The results reveal a fascinating pressure-induced thickness-dependent interlayer vibration behavior. Notably, the observed blue-shift rates of the breathing (LB) and shear (S) modes display contrasting layer-dependent behaviors. This discrepancy can be attributed to the interplay between thickness-dependent interlayer coupling and restoring forces, providing a deeper understanding of the underlying physics at play.

Additionally, the authors propose a pressure-dependent linear chain model (LCM) to characterize force constants under pressure. They also employ a bond polarization model to elucidate the intensity changeover between specific vibrational modes, shedding light on the intricacies of interlayer interactions. These findings offer a comprehensive explanation for the observed phenomena, linking them to changes in interlayer Te-Te bond angles and intralayer distances between Mo and Te atomic layers.

In summary, this research significantly contributes to our understanding of layer-dependent interlayer vibrations in MoTe₂ under high pressure. Moreover, it establishes a solid foundation for further investigations into the manipulation of interlayer coupling in Van der Waals materials through pressure engineering. Overall, the paper's findings are of great importance to the field of materials science and open up new avenues for the design and engineering of layered materials with tailored properties.