Anharmonicity and Doping Melt the Charge Density Wave in Single-Layer TiSe2.,Nano Letters

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Anharmonicity and Doping Melt the Charge Density Wave in Single-Layer TiSe2.
Nano Letters ( IF 9.6 ) Pub Date : 2020-06-04 , DOI: 10.1021/acs.nanolett.0c00597
Jianqiang Sky Zhou ₁ , Lorenzo Monacelli ₂ , Raffaello Bianco ₃ , Ion Errea _{3,

4,

5} , Francesco Mauri _{6,

7} , Matteo Calandra _{1,

8}

Affiliation

Low-dimensional systems with a vanishing band gap and a large electron–hole interaction have been proposed to be unstable toward exciton formation. As the exciton binding energy increases in low dimension, conventional wisdom suggests that excitonic insulators should be more stable in 2D than in 3D. Here we study the effects of the electron–hole interaction and anharmonicity in single-layer TiSe₂. We find that, contrary to the bulk case and to the generally accepted picture, in single-layer TiSe₂, the electron–hole exchange interaction is much smaller in 2D than in 3D and it has weak effects on phonon spectra. By calculating anharmonic phonon spectra within the stochastic self-consistent harmonic approximation, we obtain T_CDW ≈ 440 K for an isolated and undoped single layer and T_CDW ≈ 364 K for an electron-doping n = 4.6 × 10¹³ cm^–2, close to the experimental result of 200–280 K on supported samples. Our work demonstrates that anharmonicity and doping melt the charge density wave in single-layer TiSe₂.

中文翻译：

非谐性和掺杂融化了单层TiSe2中的电荷密度波。

提出了具有消失的带隙和大的电子-空穴相互作用的低维系统对激子形成不稳定。随着激子结合能在低维方向上的增加，传统观点认为，激子绝缘子在2D中应该比在3D中更稳定。在这里，我们研究了单层TiSe _2中电子-空穴相互作用和非谐性的影响。我们发现，与一般情况和普遍接受的图片相反，在单层TiSe _2中，2D中的电子-空穴交换相互作用比3D中的小得多，并且对声子光谱的影响很小。通过在随机自洽谐波近似中计算非谐声子谱，我们得到T _CDW隔离和未掺杂的单层_≈440 K，掺杂电子的T _CDW≈364 K，n = 4.6×10 ¹³ cm ^–2，接近于支持样品的200–280 K的实验结果。我们的工作表明，非谐和掺杂会熔化单层TiSe _2中的电荷密度波。

更新日期：2020-07-08

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