Npj Comput. Mater.:单极子势场与二维铁电材料—巨大位移电流效应
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Fig. 1 Crystal structure and band gap of SnTe monolayer.
近期,中国科学技术大学的金敢和何力新团队发现,在二维铁电材料SnTe中存在着巨大的位移电流效应,这一发现为太阳能转换技术打开了新的大门。位移电流是一种复杂的二阶光学效应。金敢和何力新团队运用第一性原理方法,深刻研究了SnTe单层材料的非线性光学特性。
Fig. 2 Shift current spectra, absorption, and Glass coefficient of SnTe monolayer.
他们的研究指出,这一巨大的位移电流效应源于SnTe独特的能带结构。在材料的能带结构中,位移矢量在谷点附近呈现发散现象,对非线性光学跃迁产生了显著影响。位移矢量描述了光跃迁过程中电子和空穴中心位置的相对位移。根据这一理论,导带和价带的直积态空间对应于一个黎曼空间,而位移矢量则对应于一个量子势场。在这个空间中,发散的位移矢量形成了类似单极子的势场,进而导致了巨大的位移电流效应。这种单极子特性与能带理论中描述外尔半金属的外尔点附近的贝利曲率发散相似,但它存在于一个更高维度的黎曼空间。
Fig. 3 DFT and model analysis of dipole matrix, its generalized derivatives, and shift current contribution along ky.
这一发现不仅证明了半导体材料中因位移矢量发散而产生的物理效应是可测量且具有显著的物理意义,还为未来在光电器件领域寻找具有强大位移电流效应的新型材料开辟了全新的研究方向。
Fig. 4 Quantum geometric tensor near valley point k0。
该文近期发表于npj Computational Materials 10:23(2023),英文标题与摘要如下,点击左下角“阅读原文”可以自由获取论文PDF。
Peculiar band geometry induced giant shift current in ferroelectric SnTe monolayer
Gan Jin & Lixin He
The bulk photovoltaic effect (BPVE) occurs when homogeneous noncentrosymmetric materials generate photocurrent or photovoltage under illumination. The intrinsic contribution to this effect is known as the shift current effect. We calculate the shift current conductivities of the ferroelectric SnTe monolayer using first-principles methods. Our results reveal a giant shift-current conductivity near the valley points in the SnTe monolayer. More remarkably, the linear optical absorption coefficient at this energy is very small, resulting in an enormous Glass coefficient that is four orders of magnitude larger than that of BaTiO$_3$. To understand these giant shift-current effects, we employ a three-band model and find that they arise from the nontrivial energy band geometries near the valley points, where the shift-vector diverges. This serves as a prominent example highlighting the crucial role of band geometry in determining the fundamental properties of solids.
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