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Microscopic mechanism for asymmetric charge distribution in Rashba-type surface states and the origin of the energy splitting scale

机译:Rashba型表面态中不对称电荷分布的微观机理和能量分裂尺度的起源

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摘要

The microscopic mechanism for Rashba-type band splitting is examined in detail. We show how an asymmetric charge distribution is formed when the local orbital angular momentum (OAM) and crystal momentum get interlocked due to surface effects. An electrostatic energy term in the Hamiltonian appears when such an OAM-and crystal-momentum-dependent asymmetric charge distribution is placed in an electric field produced by inversion-symmetry breaking. Analysis by using an effective Hamiltonian shows that, as the atomic spin-orbit coupling (SOC) strength increases from weak to strong, the originally OAM-quenched states evolve into well-defined chiral OAM states and then to states of total angular momentum J. In addition, the energy scale of the band splitting changes from the atomic SOC energy to electrostatic energy. To confirm the validity of the model, we study OAM and spin structures of the Au(111) system by using an effective Hamiltonian for the d-orbital case. As for the strong-SOC regime, we choose Bi_2Te_2Se as a prototype system. We performed circular dichroism angle-resolved photoemission spectroscopy experiments as well as first-principles calculations. We find that the effective model can explain various aspects of the spin and OAM structures of the system.
机译:详细研究了Rashba型谱带分裂的微观机制。我们显示了当局部轨道角动量(OAM)和晶体动量由于表面效应而互锁时,如何形成不对称电荷分布。当这种依赖于OAM和晶体动量的不对称电荷分布置于由反对称破坏产生的电场中时,就会出现哈密顿量中的静电能项。通过使用有效的哈密顿量进行的分析表明,随着原子自旋轨道耦合(SOC)强度从弱变强,最初的OAM猝灭态演变为定义明确的手性OAM态,然后发展为总角动量J的态。另外,带分裂的能级从原子SOC能量变为静电能。为了确认模型的有效性,我们通过对d轨道情况使用有效的哈密顿量研究了Au(111)系统的OAM和自旋结构。至于强SOC机制,我们选择Bi_2Te_2Se作为原型系统。我们进行了圆二色性角分辨光发射光谱实验以及第一性原理计算。我们发现有效的模型可以解释系统自旋和OAM结构的各个方面。

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