Orbital-Angular-Momentum Based Origin of Rashba-Type Surface Band Splitting

Park, Seung Ryong; Kim, Choong Hyun; Yu, Jaejun; Han, Jung Hoon; Kim, Changyoung

doi:10.1103/physrevlett.107.156803

Cited by 210 publications

(129 citation statements)

References 32 publications

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“…49, this cancellation can be understood qualitatively in a tight-binding model, where different bands have different signs of orbital chirality ± (k × L) ·ẑ. 48 The addition of spin-orbit coupling L · S then (roughly speaking) leads to alignment of the spin in the ± (k × S) ·ẑ direction, resulting in different signs of an effective Rashba parameter for different states. 49 We next attempt to identify the most important interface properties which determine the current-induced torque.…”

Section: -4mentioning

confidence: 99%

Current-induced torques and interfacial spin-orbit coupling

et al. 2013

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In bilayer systems consisting of an ultrathin ferromagnetic layer adjacent to a metal with strong spin-orbit coupling, an applied in-plane current induces torques on the magnetization. The torques that arise from spin-orbit coupling are of particular interest. Here we use first-principles methods to calculate the current-induced torque in a Pt-Co bilayer to help determine the underlying mechanism. We focus exclusively on the analog to the Rashba torque, and do not consider the spin Hall effect. The details of the torque depend strongly on the layer thicknesses and the interface structure, providing an explanation for the wide variation in results found by different groups. The torque depends on the magnetization direction in a way similar to that found for a simple Rashba model. Artificially turning off the exchange spin splitting and separately the spin-orbit coupling potential in the Pt shows that the primary source of the "fieldlike" torque is a proximate spin-orbit effect on the Co layer induced by the strong spin-orbit coupling in the Pt.

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Section: -4mentioning

confidence: 99%

Current-induced torques and interfacial spin-orbit coupling

et al. 2013

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“…The angular momentum character of the individual band can be affected by relative energy scales of the crystal field and SOC; the crystal field quenches orbital degrees of freedom, whereas SOC entangles spin and orbital degrees. Through the competition between the two energy scales, the band character on which the Rashba Hamiltonian is based can vary from the fully spin-orbital entangled total angular momentum state (J) to the spin state (S) (13), which causes a significant distinction in the angular momentum texture of the Rashba band.…”

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confidence: 99%

Switchable S = 1/2 and J = 1/2 Rashba bands in ferroelectric halide perovskites

Kim

Im²,

Freeman

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

278

306

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The Rashba effect is spin degeneracy lift originated from spinorbit coupling under inversion symmetry breaking and has been intensively studied for spintronics applications. However, easily implementable methods and corresponding materials for directional controls of Rashba splitting are still lacking. Here, we propose organic-inorganic hybrid metal halide perovskites as 3D Rashba systems driven by bulk ferroelectricity. In these materials, it is shown that the helical direction of the angular momentum texture in the Rashba band can be controlled by external electric fields via ferroelectric switching. Our tight-binding analysis and first-principles calculations indicate that S = 1=2 and J = 1=2 Rashba bands directly coupled to ferroelectric polarization emerge at the valence and conduction band edges, respectively. The coexistence of two contrasting Rashba bands having different compositions of the spin and orbital angular momentum is a distinctive feature of these materials. With recent experimental evidence for the ferroelectric response, the halide perovskites will be, to our knowledge, the first practical realization of the ferroelectric-coupled Rashba effect, suggesting novel applications to spintronic devices.electronic structure | density functional theory | effective Hamiltonian T he Rashba effect has been widely investigated in 2D surfaces, interfaces, quantum wells, and 3D bulk systems (1-6). The essential requisite for the Rashba effect is that the spin degeneracy is lifted by the inversion symmetry-breaking (ISB) field in the presence of the spin-orbit coupling (SOC). To date, major concerns have focused on enlarging Rashba strength characterized by the Rashba coefficient α R (3, 5, 6). The controllability in the direction of the ISB field, on the other hand, has not been seriously considered. In a surface or an interface, the potential gradient generated by the structural inversion asymmetry results in the loss of controllability; the field direction is mainly fixed according to the preformed surface or interface configuration. The situation is similar in recently discovered 3D Rashba material BiTeI (6), because this material has the compositional ISB field between Te and I layers.Controlling the ISB field and ultimately Rashba-type band splitting can be achieved by using a novel ferroelectric Rashba material (7,8). In a ferroelectric system, the bulk polarization controlled by external electric fields generates the ISB field. Therefore, the ferroelectric polarization directly couples to the spin splitting and the helical spin texture in the ferroelectric Rashba material, enabling the helicity reversal via the ferroelectric switching. Recent theoretical study suggested GeTe as a possible candidate for this mechanism, but the direct measurement of the ferroelectric polarization and switching is still missing due to the sizable conductivity of bulk GeTe (7,8).We consider organic-inorganic hybrid metal halide perovskites as promising ferroelectric Rashba materials. The general formula for this materia...

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“…The sixfold symmetry of the SS contours is the result of the threefold rotational symmetry of the alloy structure and time reversal symmetry. The giant SO splitting of the bands has been attributed to (i) an anisotropy in the in-plane surface potential, 4,21 (ii) the buckling of the Bi alloy layer, contributing to the anisotropy of the SS wave function along the surface normal, 24 or again iii) the unquenching of the orbital momentum at the surface, 25 Time reversal symmetry requires that the two spin branches of a Rashba system have opposite polarization, so that each branch can be considered separately in discussing their hybridization with other states. Recently, the snow-flake-like contour of the Fermi surface of Bi 2 Te 3 was simulated by adding higher order terms to an effective Hamiltonian.…”

Section: Resultsmentioning

confidence: 99%

Anisotropic spin gaps in BiAg2-Ag/Si(111)

et al. 2012

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We present a detailed analysis of the band structure of the √ 3 × √ 3 R 30 • BiAg 2 /Ag/Si(111) trilayer system by means of high resolution Angle Resolved Photoemission Spectroscopy (ARPES). BiAg 2 /Ag/Si(111) exhibits a complex spin-polarized electronic structure due to giant spin-orbit interactions. We show that a complete set of constant energy ARPES maps, supplemented by a modified nearly free electron calculation, provides a unique insight into the structure of the spin-polarized bands and spin gaps. We also show that the complex gap structure can be continuously tuned in energy by a controlled deposition of an alkali metal.

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Orbital-Angular-Momentum Based Origin of Rashba-Type Surface Band Splitting

Cited by 210 publications

References 32 publications

Current-induced torques and interfacial spin-orbit coupling

Current-induced torques and interfacial spin-orbit coupling

Switchable S = 1/2 and J = 1/2 Rashba bands in ferroelectric halide perovskites

Anisotropic spin gaps in BiAg2-Ag/Si(111)

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