A first-principles study on the Rashba effect in surface systems

Nagano, Miki; Kodama, Ayaka; Shishidou, Tatsuya; Oguchi, Tamio

doi:10.1088/0953-8984/21/6/064239

Cited by 122 publications

(135 citation statements)

References 21 publications

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“…One particularly promising candidate is the (110) surface of Au, which first-principles calculations predict will exhibit surface bands with sizeable Rashba splitting 20 . These surface bands naturally lie within 50meV of the bulk Fermi level, indicating that it should be possible to move the chemical potential into the topological regime using gating.…”

Section: Introductionmentioning

confidence: 99%

Engineering ap+ipsuperconductor: Comparison of topological insulator and Rashba spin-orbit-coupled materials

Potter¹,

Lee²

2011

Phys. Rev. B

190

150

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We compare topological insulator materials and Rashba coupled surfaces as candidates for engineering p+ip superconductivity. Specifically, in each type of material we examine 1) the limitations to inducing superconductivity by proximity to an ordinary s-wave superconductor, and 2) the robustness of the resulting superconductivity against disorder. We find that topological insulators have strong advantages in both regards: there are no fundamental barriers to inducing superconductivity, and the induced superconductivity is immune to disorder. In contrast, for Rashba coupled quantum wires or surface states, the the achievable gap from induced superconductivity is limited unless the Rashba coupling is large. Furthermore, for small Rashba coupling the induced superconductivity is strongly susceptible to disorder. These features pose serious difficulties for realizing p+ip superconductors in semiconductor materials due to their weak spin-orbit coupling, and suggest the need to seek alternatives. Some candidate materials are discussed.

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Section: Introductionmentioning

confidence: 99%

Engineering ap+ipsuperconductor: Comparison of topological insulator and Rashba spin-orbit-coupled materials

Potter¹,

Lee²

2011

Phys. Rev. B

190

150

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“…This energy scale is then one order of magnitude larger than both the one so far reported in LaAlO 3 /SrTiO 3 interfaces [10,11], and the one expected from a naive Rashba model that takes solely into account the confining electric field. Such a strong deviation from the original Rashba scenario has been demonstrated for model metallic systems by numerous previous works [23,24], and is attributed as a general property of the surface corrugation and the associated wave-function asymmetry [23][24][25][26], which results in a greatly enhanced Rashba parameter that increases the spin splitting. Thus, the large spin splitting of helical spin texture observed in our data may signal the relevance of surface corrugations for understanding the electronic and spin structure of the 2DEG at the surface of SrTiO 3 .…”

mentioning

confidence: 74%

Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

et al. 2014

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1 Two-dimensional electron gases (2DEGs) forming at the interfaces of transition metal oxides [1][2][3] display a range of properties including tunable insulatorsuperconductor-metal transitions [4][5][6], large magnetoresistance [7], coexisting ferromagnetism and superconductivity [8, 9], and a spin splitting of a few meV [10,11]. Strontium titanate (SrTiO 3 ), the cornerstone of such oxide-based electronics, is a transparent, nonmagnetic, wide-band-gap insulator in the bulk, and has recently been found to host a surface 2DEG [12][13][14][15]. The most strongly confined carriers within this 2DEG comprise two sub-bands, separated by an energy gap of 90 meV and forming concentric circular Fermi surfaces [12,13,15].Using spin-and angle-resolved photoemission spectroscopy (SARPES), we show that the electron spins in these sub-bands have opposite chiralities. Although the Rashba effect might be expected to give rise to such spin textures, the giant splitting of almost 100 meV at the Fermi level is far larger than anticipated [16,17].Moreover, in contrast to a simple Rashba system, the spin-polarized sub-bands are non-degenerate at the Brillouin zone centre. This degeneracy can be lifted by time-reversal symmetry breaking, implying the possible existence of magnetic order. These results show that confined electronic states at oxide surfaces can be endowed with novel, non-trivial properties that are both theoretically challenging to anticipate and promising for technological applications.The 2DEG at the surface of SrTiO 3 , formed by confined electrons of the t 2g conduction band with Ti-3d character, is universal in the sense that its constituent subbands, their fillings, and their Fermi surfaces are independent of the bulk sample doping and of whether the surfaces are prepared by cleaving [12,13] or by etching and in situ annealing [15]. This 2DEG consists on two light electron subbands dispersing down to about −180 meV and, respectively, −90 meV below the Fermi level (E F ), producing concentric Fermi surfaces around the Brillouin zone center, and heavy shallow subbands dispersing down to about −40 meV, forming ellipsoidal Fermi surfaces [12,13,15].In fact, the 2DEG in SrTiO 3 has been associated with a band-bending of ∼ 300 meV at the surface of the material [12,13,15]. In such a quantum well profile, the most bound light subbands are tightly confined near the surface, while the less bound heavy subbands are more delocalized towards the bulk [12,15]. The present work focuses on resolving the spin 2 structure of the strongly two-dimensional light subbands, which are the most technologically relevant in terms of their carrier concentration and mobility.The surface band-bending of ∼ 300 meV amounts to an electric field F ∼ 100 MV/m confining the conduction electrons near the surface. In a simple approximation, this field will induce a so-called "Rashba splitting" of the spin states in each subband, with the largest splitting occurring for the most bound subbands. In an ideal surface, the corresponding momentum separat...

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“…This is because the assumption of nearly free 2DEG, which ignores the region of ion cores and the asymmetric feature of the interface wavefunction, is too simple. In reality, the expression for ∆ R is much more complicated [17][18][19][20][21] and usually treated as a fitting parameter in semiconductor heterostructures and metal surfaces.…”

mentioning

confidence: 99%

Theory of spin-orbit coupling at LaAlO3/SrTiO3interfaces and SrTiO3surfaces

2013

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The theoretical understanding of the spin-orbit coupling (SOC) effects at LaAlO3/SrTiO3 interfaces and SrTiO3 surfaces is still in its infancy. We perform first-principles density-functional-theory calculations and derive from these a simple tight-binding Hamiltonian, through a Wannier function projection and group theoretical analysis. We find striking differences to the standard Rashba theory for spin-orbit coupling in semiconductor heterostructures due to multi-orbital effects: by far the biggest SOC effect is at the crossing point of the xy and yz (or zx) orbitals; and around the Γ point a Rashba spin splitting with a cubic dependence on the wave vector k is possible.

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A first-principles study on the Rashba effect in surface systems

Cited by 122 publications

References 21 publications

Engineering ap+ipsuperconductor: Comparison of topological insulator and Rashba spin-orbit-coupled materials

Engineering ap+ipsuperconductor: Comparison of topological insulator and Rashba spin-orbit-coupled materials

Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

Theory of spin-orbit coupling at LaAlO3/SrTiO3interfaces and SrTiO3surfaces

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