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Hierarchical spin-orbital polarization of a giant Rashba system.

Bawden L, Riley JM, Kim CH, Sankar R, Monkman EJ, Shai DE, Wei HI, Lochocki EB, Wells JW, Meevasana W, Kim TK, Hoesch M, Ohtsubo Y, Le Fèvre P, Fennie CJ, Shen KM, Chou F, King PD - Sci Adv (2015)

Bottom Line: The Rashba effect is one of the most striking manifestations of spin-orbit coupling in solids and provides a cornerstone for the burgeoning field of semiconductor spintronics.Combining polarization-dependent and resonant angle-resolved photoemission measurements with density functional theory calculations, we show that the two "spin-split" branches of the model giant Rashba system BiTeI additionally develop disparate orbital textures, each of which is coupled to a distinct spin configuration.This necessitates a reinterpretation of spin splitting in Rashba-like systems and opens new possibilities for controlling spin polarization through the orbital sector.

View Article: PubMed Central - PubMed

Affiliation: SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, UK.

ABSTRACT
The Rashba effect is one of the most striking manifestations of spin-orbit coupling in solids and provides a cornerstone for the burgeoning field of semiconductor spintronics. It is typically assumed to manifest as a momentum-dependent splitting of a single initially spin-degenerate band into two branches with opposite spin polarization. Combining polarization-dependent and resonant angle-resolved photoemission measurements with density functional theory calculations, we show that the two "spin-split" branches of the model giant Rashba system BiTeI additionally develop disparate orbital textures, each of which is coupled to a distinct spin configuration. This necessitates a reinterpretation of spin splitting in Rashba-like systems and opens new possibilities for controlling spin polarization through the orbital sector.

No MeSH data available.


Disentangling intertwined atomic and orbital characters.(A) Fermi level momentum distribution curve (EF ±15 meV) measured along Γ–M as a function of probing photon energy using p-polarized light. No dispersion is observed, indicating 2D states consistent with our assignment of quantum well subbands, whereas strong matrix element variations give rise to pronounced intensity modulations. (B) Extracted spectral weight of the outermost band (kF ≈ −0.2 Å−1) as a function of binding energy, revealing characteristic intensity enhancement due to resonant photoemission at the Bi O-edge. (C and D) Corresponding dispersions (along Γ–M) measured on-resonance (hν = 28 eV) and off-resonance (hν = 30 eV), respectively, with p-polarized (left) and s-polarized (center) light. The difference in spectral weight between these dispersions (right) indicates a band and element-dependent orbital polarization.
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Figure 2: Disentangling intertwined atomic and orbital characters.(A) Fermi level momentum distribution curve (EF ±15 meV) measured along Γ–M as a function of probing photon energy using p-polarized light. No dispersion is observed, indicating 2D states consistent with our assignment of quantum well subbands, whereas strong matrix element variations give rise to pronounced intensity modulations. (B) Extracted spectral weight of the outermost band (kF ≈ −0.2 Å−1) as a function of binding energy, revealing characteristic intensity enhancement due to resonant photoemission at the Bi O-edge. (C and D) Corresponding dispersions (along Γ–M) measured on-resonance (hν = 28 eV) and off-resonance (hν = 30 eV), respectively, with p-polarized (left) and s-polarized (center) light. The difference in spectral weight between these dispersions (right) indicates a band and element-dependent orbital polarization.

Mentions: Although typically treated in a single-band picture, the electronic wave function for each branch of a Rashba-split state can be more generally written as , where, following the notation in (18), i is the atomic index, τ ∈ {px, py, pz} and σ are the orbital and spin indices, respectively, ψi,τ are atomic wave functions, and are complex coefficients. Neglecting spin-orbit coupling, our calculations predict a conduction band in BiTeI predominantly derived from Bi pz orbitals (see fig. S2). Including such effects, however, not only permits it to become strongly spin-split via Rashba-like interactions but also promotes significant orbital mixing. In general, therefore, multiple can be expected to become nonnegligible. For a complete description of the Rashba-split states, it is therefore essential to consider the interplay of the underlying atomic, orbital, and spin components. To disentangle these contributions, we combine two powerful features of ARPES: characteristic selection rules for photoemission using linearly polarized light, allowing us to directly probe the orbital wave function (19, 20), and resonant photoemission to provide elemental sensitivity (21). Such resonant enhancements are evident in Fig. 2 (A and B). They cause the spectral weight of the conduction band states to strongly peak at photon energies around 26 and 28 eV, close in energy to the binding energy of the Bi 5d5/2,3/2 core levels, with functional forms that are well described by Fano line shapes. This points to a significant Bi-derived atomic character of the lowest conduction band states, consistent with theoretical calculations (22). We exploit this, selectively probing “on-resonance” to unveil the Bi-projected spectral function.


Hierarchical spin-orbital polarization of a giant Rashba system.

Bawden L, Riley JM, Kim CH, Sankar R, Monkman EJ, Shai DE, Wei HI, Lochocki EB, Wells JW, Meevasana W, Kim TK, Hoesch M, Ohtsubo Y, Le Fèvre P, Fennie CJ, Shen KM, Chou F, King PD - Sci Adv (2015)

Disentangling intertwined atomic and orbital characters.(A) Fermi level momentum distribution curve (EF ±15 meV) measured along Γ–M as a function of probing photon energy using p-polarized light. No dispersion is observed, indicating 2D states consistent with our assignment of quantum well subbands, whereas strong matrix element variations give rise to pronounced intensity modulations. (B) Extracted spectral weight of the outermost band (kF ≈ −0.2 Å−1) as a function of binding energy, revealing characteristic intensity enhancement due to resonant photoemission at the Bi O-edge. (C and D) Corresponding dispersions (along Γ–M) measured on-resonance (hν = 28 eV) and off-resonance (hν = 30 eV), respectively, with p-polarized (left) and s-polarized (center) light. The difference in spectral weight between these dispersions (right) indicates a band and element-dependent orbital polarization.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643772&req=5

Figure 2: Disentangling intertwined atomic and orbital characters.(A) Fermi level momentum distribution curve (EF ±15 meV) measured along Γ–M as a function of probing photon energy using p-polarized light. No dispersion is observed, indicating 2D states consistent with our assignment of quantum well subbands, whereas strong matrix element variations give rise to pronounced intensity modulations. (B) Extracted spectral weight of the outermost band (kF ≈ −0.2 Å−1) as a function of binding energy, revealing characteristic intensity enhancement due to resonant photoemission at the Bi O-edge. (C and D) Corresponding dispersions (along Γ–M) measured on-resonance (hν = 28 eV) and off-resonance (hν = 30 eV), respectively, with p-polarized (left) and s-polarized (center) light. The difference in spectral weight between these dispersions (right) indicates a band and element-dependent orbital polarization.
Mentions: Although typically treated in a single-band picture, the electronic wave function for each branch of a Rashba-split state can be more generally written as , where, following the notation in (18), i is the atomic index, τ ∈ {px, py, pz} and σ are the orbital and spin indices, respectively, ψi,τ are atomic wave functions, and are complex coefficients. Neglecting spin-orbit coupling, our calculations predict a conduction band in BiTeI predominantly derived from Bi pz orbitals (see fig. S2). Including such effects, however, not only permits it to become strongly spin-split via Rashba-like interactions but also promotes significant orbital mixing. In general, therefore, multiple can be expected to become nonnegligible. For a complete description of the Rashba-split states, it is therefore essential to consider the interplay of the underlying atomic, orbital, and spin components. To disentangle these contributions, we combine two powerful features of ARPES: characteristic selection rules for photoemission using linearly polarized light, allowing us to directly probe the orbital wave function (19, 20), and resonant photoemission to provide elemental sensitivity (21). Such resonant enhancements are evident in Fig. 2 (A and B). They cause the spectral weight of the conduction band states to strongly peak at photon energies around 26 and 28 eV, close in energy to the binding energy of the Bi 5d5/2,3/2 core levels, with functional forms that are well described by Fano line shapes. This points to a significant Bi-derived atomic character of the lowest conduction band states, consistent with theoretical calculations (22). We exploit this, selectively probing “on-resonance” to unveil the Bi-projected spectral function.

Bottom Line: The Rashba effect is one of the most striking manifestations of spin-orbit coupling in solids and provides a cornerstone for the burgeoning field of semiconductor spintronics.Combining polarization-dependent and resonant angle-resolved photoemission measurements with density functional theory calculations, we show that the two "spin-split" branches of the model giant Rashba system BiTeI additionally develop disparate orbital textures, each of which is coupled to a distinct spin configuration.This necessitates a reinterpretation of spin splitting in Rashba-like systems and opens new possibilities for controlling spin polarization through the orbital sector.

View Article: PubMed Central - PubMed

Affiliation: SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, Fife KY16 9SS, UK.

ABSTRACT
The Rashba effect is one of the most striking manifestations of spin-orbit coupling in solids and provides a cornerstone for the burgeoning field of semiconductor spintronics. It is typically assumed to manifest as a momentum-dependent splitting of a single initially spin-degenerate band into two branches with opposite spin polarization. Combining polarization-dependent and resonant angle-resolved photoemission measurements with density functional theory calculations, we show that the two "spin-split" branches of the model giant Rashba system BiTeI additionally develop disparate orbital textures, each of which is coupled to a distinct spin configuration. This necessitates a reinterpretation of spin splitting in Rashba-like systems and opens new possibilities for controlling spin polarization through the orbital sector.

No MeSH data available.