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arXiv 1602.08256cond-mat.mtrl-sci
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半金属WTe2表面Rashba型自旋分裂的干涉证据

Interference Evidence for Rashba-Type Spin-Split on Semimetallic WTe2 Surface

Qing Li, Jiaqiang Yan, Biao Yang, Yunyi Zang, Junjie Zhang, Ke He, Menghao Wu, Yanfei Zhao, David Mandrus, Jian Wang, Qikun Xue, Lifeng Chi, David J. Singh, Minghu Pan

摘要:

半金属二碲化钨(WTe 2)显示出极大的非饱和磁电阻(XMR),这是人们强烈感兴趣的主题。这种现象被认为是由于完美的n-p电荷补偿与WTe 2中的低载流子密度的结合以及其能带结构的可能细节引起的。最近,通过角分辨光电子能谱(ARPES)在WTe 2中观察到了由强自旋轨道耦合(SOC)引起的“自旋织构”。这提供了一种机制,用于保护所涉及的状态的后向散射,因此被提议在WTe 2的XMR中发挥重要作用。在这里,基于我们对体WTe 2的密度泛函计算,我们发现由于其非中心对称结构,在计算的能带结构中存在强烈的Rashba自旋轨道效应。这使能带分裂,并提升了能带的二重自旋简并度。通过扫描隧道显微镜(STM)测量,在4.2K下观察到了WTe 2表面的Umklapp干涉条纹(一种涉及倒易晶格矢量的光谱特征)。这与在77 K下所证明的表面原子结构明显不同。Umklapp干涉的能量依赖性与ARPES测量积分的态密度有很强的对应关系,表明带在Gamma点的对侧是自旋分裂的。光谱测量揭示了电子/空穴不对称性的比例沿b轴的横向位置交替变化,提供了半金属WTe 2的双载流子输运的微观图像。计算的能带结构和费米面得到了ARPES结果和Shubnikov-de Haas(SdH)振荡测量的进一步支持。

英文摘要:

Semimetallic tungsten ditelluride (WTe2) displays an extremely large non-saturating magnetoresistance (XMR), which is the subject of intense interest. This phenomenon is thought to arise from the combination of perfect n-p charge compensation with low carrier densities in WTe2 and presumably details of its band structure. Recently, "spin texture" induced by strong spin-orbital coupling (SOC) has been observed in WTe2 by angle-resolved photoemission spectroscopy (ARPES). This provides a mechanism for protecting backscattering for the states involved and thus was proposed to play an important role in the XMR of WTe2. Here, based on our density functional calculations for bulk WTe2, we found a strong Rashba spin-orbit effect in the calculated band structure due to its non-centrosymmetric structure. This splits bands and two-fold spin degeneracy of bands is lifted. A prominent Umklapp interference pattern (a spectroscopic feature with involving reciprocal lattice vectors) can be observed by scanning tunneling microscopic (STM) measurements on WTe2 surface at 4.2 K. This differs distinctly from the surface atomic structure demonstrated at 77 K. The energy dependence of Umklapp interference shows a strong correspondence with densities of states integrated from ARPES measurement, manifesting a fact that the bands are spin-split on the opposites side of Gamma point. Spectroscopic survey reveals the ratio of electron/hole asymmetry changes alternately with lateral locations along b axis, providing a microscopic picture for double-carrier transport of semimetallic WTe2. The calculated band structure and Fermi surface is further supported by our ARPES results and Shubnikov-de Haas (SdH) oscillations measurements.

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