Electrostatic doping-assisted phonon softening has been intensively investigated in semiconducting transition metal dichalcogenides (TMDCs), in which strong electron–phonon interactions can be achieved in thin layers. Though electron–phonon coupling plays an important role in structure phase transitions for metallic 2H-TaX₂ (X = S, Se), it has been rarely studied under electrostatic doping. Here, the effect of electrostatic doping on the vibrational phonon modes of 2H-TaSe₂ and 2H-TaS₂ thin films is studied with ionic liquid gating by the electric-double-layer gating technique. Under a gate bias (V_G) of 1.5 V, 2H-TaSe₂ has a blue shift of 7 cm⁻¹ and a red shift of 3 cm⁻¹ for the in-plane (E_2g) and out-of-plane vibration (A_1g) modes, respectively, indicating a strong electron–phonon interaction in both intralayer and interlayer. By varying the thickness of the flakes, it has been found that there exists a threshold V_G value for the stiffening of the E_2g mode and the softening of the A_1g mode because of the strong electrostatic screening effect at lower doping density. As the intensity of the E_2g mode decreases with V_G, an anomalous enhancement of the A_1g phonons can be achieved, which is further convinced in TaS₂. The asymmetric phonon evolution behavior is very different with that in the semiconducting TMDCs, which may provide useful information for understanding electron–phonon interplay in metallic layer materials.

中文翻译：

---

静电掺杂 2H-TaX2(X = S/Se) 薄片中声子模式的研究

静电掺杂辅助声子软化已在半导体过渡金属二硫属化物（TMDC）中得到深入研究，其中可以在薄层中实现强电子 - 声子相互作用。尽管电子-声子耦合在金属 2H-TaX ₂ (X = S, Se) 的结构相变中起着重要作用，但在静电掺杂下很少对其进行研究。在这里，静电掺杂对 2H-TaSe ₂和 2H-TaS ₂薄膜振动声子模式的影响通过双电层门控技术用离子液体门控进行研究。在1.5 V的栅极偏压 ( V _G ) 下，2H-TaSe ₂具有 7 cm ^-1的蓝移和 3 cm 的红移^{-1 分别}表示面内 (E _2g ) 和面外振动 (A _1g ) 模式，表明层内和层间都存在强电子-声子相互作用。通过改变薄片的厚度，已经发现由于在较低掺杂密度下的强静电屏蔽效应，E _2g模式的硬化和A _1g模式的软化存在阈值V _G值。随着 E _2g模式的强度随V _G降低，可以实现A _1g声子的异常增强，这在 TaS _{2 中}得到进一步证实. 不对称声子演化行为与半导体 TMDC 中的不对称声子演化行为非常不同，这可能为理解金属层材料中的电子 - 声子相互作用提供有用的信息。