Structural Phase Transition and Material Properties of Few-Layer Monochalcogenides.
Structural Phase Transition and Material Properties of Few-Layer Monochalcogenides.
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DOI：
10.1103/physrevlett.117.246802
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发表时间：
2016-03
影响因子：
8.6
通讯作者：
Mehrshad Mehboudi;Benjamin M. Fregoso;Yurong Yang;Wenjuan Zhu;A. V. D. Zande;J. Ferrer;L. Bellaiche
中科院分区：
文献类型：
--
作者：
Mehrshad Mehboudi;Benjamin M. Fregoso;Yurong Yang;Wenjuan Zhu;A. V. D. Zande;J. Ferrer;L. Bellaiche
GeSe和SnSe单硫族化合物单层膜和双层膜在低于熔点的临界温度Tc下经历了从矩形晶胞到方形晶胞的二维相变。它对材料性能的后果进行了研究的框架内的Car-Parrinello分子动力学和密度泛函理论。当相变发生时，没有带隙态的形成，因此相变材料在T_{c}以下和T_{c}以上都是半导体。当面内晶格在T_{c}处由矩形转变为正方形时，其电子、自旋、光学和压电性质与先前的预测显著不同。实际上，布里渊区中的Y点和X点在T_{c}处变得有效等效，导致对称的电子结构。在T_{c}处，空穴电导率出现反常的热增长，在T_{c}处，空穴电导率的自旋极化消失。线性光学吸收带边也必须改变其偏振，使这种结构和电子演化可通过光学手段验证。这些材料中的巨压电性和铁电性的理论预测引起了人们的极大兴奋，我们估计热释电响应约为3×10^{-12} C/Km。这些结果揭示了温度作为一个控制旋钮的几层IV族单硫族化合物的物理性质的基本作用。
GeSe and SnSe monochalcogenide monolayers and bilayers undergo a two-dimensional phase transition from a rectangular unit cell to a square unit cell at a critical temperature T_{c} well below the melting point. Its consequences on material properties are studied within the framework of Car-Parrinello molecular dynamics and density-functional theory. No in-gap states develop as the structural transition takes place, so that these phase-change materials remain semiconducting below and above T_{c}. As the in-plane lattice transforms from a rectangle into a square at T_{c}, the electronic, spin, optical, and piezoelectric properties dramatically depart from earlier predictions. Indeed, the Y and X points in the Brillouin zone become effectively equivalent at T_{c}, leading to a symmetric electronic structure. The spin polarization at the conduction valley edge vanishes, and the hole conductivity must display an anomalous thermal increase at T_{c}. The linear optical absorption band edge must change its polarization as well, making this structural and electronic evolution verifiable by optical means. Much excitement is drawn by theoretical predictions of giant piezoelectricity and ferroelectricity in these materials, and we estimate a pyroelectric response of about 3×10^{-12} C/K m here. These results uncover the fundamental role of temperature as a control knob for the physical properties of few-layer group-IV monochalcogenides.