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arXiv 1503.05004cond-mat.mtrl-sci
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铁电α- GeTe(111)半导体中巨Rashba分裂的表面与体相贡献

Surface versus bulk contributions to the giant Rashba splitting in the ferroelectric α-GeTe(111) semiconductor

J. Krempaský, H. Volfová, S. Muff, N. Pilet, G. Landolt, M. Radović, M. Shi, D. Kriegner, V. Holý, J. Braun, H. Ebert, F. Bisti, V. A. Rogalev, V. N. Strocov, G… 展开作者

J. Krempaský, H. Volfová, S. Muff, N. Pilet, G. Landolt, M. Radović, M. Shi, D. Kriegner, V. Holý, J. Braun, H. Ebert, F. Bisti, V. A. Rogalev, V. N. Strocov, G. Springholz, J. Minár, J. H. Dil

摘要:

在具有破缺反转对称性的系统中,自旋轨道耦合(SOC)产生电子态的Rashba型自旋分裂,表现为带的k依赖分裂。虽然以前大多数研究都集中在二维电子系统上,但最近在一系列碲化铋中发现了这种拉什巴效应的三维(3D)形式。尽管这些材料表现出非常大的自旋分裂,但它们缺乏关于功能化的重要性质,即切换或调节自旋织构的可能性。这种限制可以在一类新的功能材料中克服,这些材料显示Rashba分裂耦合到铁电性:铁电Rashba半导体(FERS)。使用自旋和角度分辨光电子能谱(SARPES),我们表明,GeTe(111)形成了这一类的主要成员,显示复杂的自旋纹理的Rashba分裂表面和体带所产生的本征反转对称性破缺所造成的铁电极化体(FE)。除了纯粹的表面和体状态,我们发现表面-体共振态(SBR)的波函数纠缠的旋量从体积和表面的贡献。在费米能级,它们的杂化导致非常规的自旋拓扑结构,具有共手性螺旋和伴随的能隙开放。GeTe(111)表面和SBR态使半导体表面导电。同时,我们的SARPES数据证实了GeTe是一种窄禁带半导体,这表明GeTe(111)电子态具有理论上难以预测的自旋特性。由于Rashba带中自旋的螺旋度与FE极化的方向有关,因此这项工作为半导体自旋输运性质的全电非易失性控制铺平了道路。

英文摘要:

In systems with broken inversion symmetry spin-orbit coupling (SOC) yields a Rashba-type spin splitting of electronic states, manifested in a k-dependent splitting of the bands. While most research had previously focused on 2D electron systems, recently a three-dimensional (3D) form of such Rashba-effect was found in a series of bismuth tellurohalides. Whereas these materials exhibit a very large spin-splitting, they lack an important property concerning functionalization, namely the possibility to switch or tune the spin texture. This limitation can be overcome in a new class of functional materials displaying Rashba-splitting coupled to ferroelectricity: the ferroelectric Rashba semiconductors (FERS). Using spin- and angle-resolved photoemission spectroscopy (SARPES) we show that GeTe(111) forms a prime member of this class, displaying a complex spin-texture for the Rashba-split surface and bulk bands arising from the intrinsic inversion symmetry breaking caused by the ferroelectric polarization of the bulk (FE). Apart from pure surface and bulk states we find surface-bulk resonant states (SBR) whose wavefunctions entangle the spinors from the bulk and surface contributions. At the Fermi level their hybridization results in unconventional spin topologies with cochiral helicities and concomitant gap opening. The GeTe(111) surface and SBR states make the semiconductor surface conducting. At the same time our SARPES data confirm that GeTe is a narrow-gap semiconductor, suggesting that GeTe(111) electronic states are endowed with spin properties that are theoretically challenging to anticipate. As the helicity of the spins in Rashba bands is connected to the direction of the FE polarization, this work paves the way to all-electric non-volatile control of spin-transport properties in semiconductors.

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