Origin of giant bulk Rashba splitting: Application to BiTeI

Bahramy, M. S.; Arita, Ryotaro; Nagaosa, Naoto

doi:10.1103/physrevb.84.041202

Cited by 214 publications

(283 citation statements)

References 18 publications

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“…We also find a small spin splitting of these valence band quantum well states, which is not resolved experimentally. Its location, around the top of their M-shaped dispersions, indicates a subtle interplay of spin-orbit interactions between the valence and conduction band subbands 29 . Thus, a hierarchy of electronic states in both energy and spatial extent is created, spanning from the two-dimensional limit of the TSS and lowest subbands of the conduction and valence bands to the three-dimensional continuum (Fig.…”

Section: Resultsmentioning

confidence: 99%

Emergent quantum confinement at topological insulator surfaces

et al. 2012

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Bismuth-chalchogenides are model examples of three-dimensional topological insulators. Their ideal bulk-truncated surface hosts a single spin-helical surface state, which is the simplest possible surface electronic structure allowed by their non-trivial Z 2 topology. However, real surfaces of such compounds, even if kept in ultra-high vacuum, rapidly develop a much more complex electronic structure whose origin and properties have proved controversial. Here we demonstrate that a conceptually simple model, implementing a semiconductor-like band bending in a parameter-free tight-binding supercell calculation, can quantitatively explain the entire measured hierarchy of electronic states. In combination with circular dichroism in angle-resolved photoemission experiments, we further uncover a rich three-dimensional spin texture of this surface electronic system, resulting from the non-trivial topology of the bulk band structure. Moreover, our study sheds new light on the surface-bulk connectivity in topological insulators, and reveals how this is modified by quantum confinement.

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Section: Resultsmentioning

confidence: 99%

Emergent quantum confinement at topological insulator surfaces

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“…2(h) accords well with the band structure obtained by SX-ARPES. The CB, HVB, and the deepest VB show moderately strong k z -dependence (0.4 ∼ 0.8 eV) as compared to other bands (< 0.2 eV), since they are mainly characterized by Bi 6p z , Te 5p z , and I 5p z , respectively [14]. Still they are apparently weaker than the in-plane dispersions.…”

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confidence: 94%

“…This huge spin-splitting has been successfully explained by means of k · p perturbation theory [14]. According to the theory, the SOI-induced band splitting near the Fermi level ( i.e.…”

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confidence: 99%

“…1(a)], it also shows a Rashba-type spin splitting similar to the ones observed in 2-dimensional surface Shockley states. Quantitative agreements between the (spin-resolved) ARPES and the first-principles calculations, together with the optical study on the bulk state, strongly suggest that the spin splitting is derived from bulk BiTeI [13,14,15]. Nevertheless, the direct observation of 3-dimensional (3D) spin-splitting beyond Bychkov-Rashba model has not been investigated to date.…”

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Three-dimensional bulk band dispersion in polar BiTeI with giant Rashba-type spin splitting

et al. 2012

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In layered polar semiconductor BiTeI, giant Rashba-type spin-split band dispersions show up due to the crystal structure asymmetry and the strong spin-orbit interaction. Here we investigate the 3-dimensional (3D) bulk band structures of BiTeI using the bulk-sensitive hν-dependent soft x-ray angle resolved photoemission spectroscopy (SX-ARPES). The obtained band structure is shown to be well reproducible by the first-principles calculations, with huge spin splittings of ∼300 meV at the conduction-band-minimum and valence-band-maximum located in the k z = π/c plane.It provides the first direct experimental evidence of the 3D Rashba-type spin splitting in a bulk compound.

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“…The Rashba-type splitting of the fully spin-orbital-entangled J = 1=2 subspace stems from the bandgapindependent intraorbital as well as the bandgap-dependent interorbital terms. On the contrary, S = 1=2 Rashba splitting only consists of the interorbital term (14). We present several examples of possible ferroelectric Rashba materials (β-MAPbI 3 , β-MASnI 3 , and ortho-MASbBr 3 ) by adopting first-principles electronic structure calculations based on density functional theory.…”

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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

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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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Origin of giant bulk Rashba splitting: Application to BiTeI

Cited by 214 publications

References 18 publications

Emergent quantum confinement at topological insulator surfaces

Emergent quantum confinement at topological insulator surfaces

Three-dimensional bulk band dispersion in polar BiTeI with giant Rashba-type spin splitting

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

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