Imaging Ultrafast Dynamics of Pressure-Driven Phase Transitions in Black Phosphorus and Anomalous Coherent Phonon Softening,Nano Letters

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Imaging Ultrafast Dynamics of Pressure-Driven Phase Transitions in Black Phosphorus and Anomalous Coherent Phonon Softening
Nano Letters ( IF 9.6 ) Pub Date : 2023-12-28 , DOI: 10.1021/acs.nanolett.3c04218
Simin Wu ₁ , Weibin Chu _{1,

2} , Yang Lu _{3,

4} , Minbiao Ji _{1,

5}

Affiliation

Applying high pressure to effectively modulate the electronic and lattice structures of materials could unravel various physical properties associated with phase transitions. In this work, high-pressure-compatible femtosecond pump–probe microscopy was constructed to study the pressure-dependent ultrafast dynamics in black phosphorus (BP) thin films. We observed pressure-driven evolution of the electronic topological transition and three structural phases as the pressure reached ∼22 GPa, which could be clearly differentiated in the transient absorption images containing spatially resolved ultrafast carrier and coherent phonon dynamics. Surprisingly, an anomalous coherent acoustic phonon mode with pressure softening behavior was observed within the range of ∼3–8 GPa, showing distinct laser power and time dependences. Density functional theory calculations show that this mode, identified as the shear mode along the armchair orientation, gains significant electron–phonon coupling strength from out-of-plane compression that leads to decreased phonon frequency. Our results provide insights into the structure evolution of BP with pressure and hold potential for applications in microelectromechanical devices.

中文翻译：

黑磷中压力驱动相变的超快动力学成像和反常相干声子软化

施加高压来有效调节材料的电子和晶格结构可以揭示与相变相关的各种物理特性。在这项工作中，构建了高压兼容的飞秒泵浦探针显微镜来研究黑磷（BP）薄膜中压力依赖性超快动力学。当压力达到~22 GPa时，我们观察到了电子拓扑转变和三个结构相的压力驱动演化，这可以在包含空间分辨超快载流子和相干声子动力学的瞬态吸收图像中清楚地区分。令人惊讶的是，在 ~3-8 GPa 范围内观察到具有压力软化行为的反常相干声子模式，显示出明显的激光功率和时间依赖性。密度泛函理论计算表明，这种模式被称为沿扶手椅方向的剪切模式，通过面外压缩获得显着的电子声子耦合强度，从而导致声子频率降低。我们的研究结果提供了有关 BP 随压力的结构演变的见解，并具有在微机电设备中应用的潜力。

更新日期：2023-12-28

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