Microscopic mechanism for the Rashba spin-band splitting: Perspective from formation of local orbital angular momentum

Park, Seung Ryong; Kim, Changyoung

doi:10.1016/j.elspec.2014.12.009

Cited by 32 publications

(25 citation statements)

References 37 publications

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“…Spatial inversion symmetry is sufficiently common in the crystal structures of materials that the constraints it places on electronic wavefunctions, notably parity, often underpin our understanding of physics. In materials that lack spatial inversion symmetry, a variety of additional terms can be present in the Hamiltonian, such as Dzyaloshinskii-Moriya terms in magnets 1,2 , Rashba-Dresselhaus spin-orbit band splitting 3,4 , or additional Coulomb terms [5][6][7][8] . These compete with existing interactions, and can lead to a rich array of entirely new physics either on their own or through that competition.…”

Section: Introductionmentioning

confidence: 99%

Physical properties of noncentrosymmetric tungsten and molybdenum aluminides

Peets¹,

Ying²,

Shen³

et al. 2018

Phys. Rev. Materials

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A lack of spatial inversion symmetry gives rise to a variety of unconventional physics, from noncollinear order and Skyrmion lattice phases in magnetic materials to topologically-protected surface states in certain band insulators, to mixed-parity pairing states in superconductors. The search for exotic physics in such materials is largely limited by a lack of candidate materials, and often by difficulty in obtaining crystals. Here, we report the single crystal growth and physical properties of the noncentrosymmetric tungsten aluminide cage compounds Al4W and Al5W, alongside related molybdenum aluminides in which spin-orbit coupling should be significantly weaker. All compounds are nonmagnetic metals. Their high conductivities suggest the opportunity to find superconductivity at lower temperatures, while the limits we can place on their transition temperatures suggest that any superconductivity may be expected to exhibit significant parity mixing. arXiv:1807.03476v2 [cond-mat.mtrl-sci]

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Section: Introductionmentioning

confidence: 99%

Physical properties of noncentrosymmetric tungsten and molybdenum aluminides

Peets¹,

Ying²,

Shen³

et al. 2018

Phys. Rev. Materials

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“…This indicates a regime where the achievable spinsplitting is, in fact, limited by E ISB , typically to only a modest percentage of the atomic SOC ( Fig. 1(a)) [36][37][38] . If, however, an ISB energy scale can be achieved which is significantly larger than the SOC, the spin-orbit Hamiltonian will act as a perturbation to a Hamiltonian dominated by the ISB.…”

mentioning

confidence: 97%

“…The weaker spin-orbit interaction cannot mix those states, instead further spin-splitting them into states of spin parallel and antiparallel to the preexisting OAM, with a splitting that must therefore take the full atomic SOC value ( Fig. 1(b)) [36][37][38] . This is clearly a desirable limit to maximise the achievable spin-splitting for a given strength of SOC, but is typically only realised when the absolute value of SOC, and consequently also the total spin splitting, is small.…”

mentioning

confidence: 99%

Maximal Rashba-like spin splitting via kinetic-energy-coupled inversion-symmetry breaking

Sunko¹,

Rösner²,

Kushwaha³

et al. 2017

Nature

143

102

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Engineering and enhancing inversion symmetry breaking in solids is a major goal in condensed matter physics and materials science, as a route to advancing new physics and applications ranging from improved ferroelectrics for memory devices to materials hosting Majorana zero modes for quantum computing. Here, we uncover a new mechanism for realising a much larger energy scale of inversion symmetry breaking at surfaces and interfaces than is typically achieved. The key ingredient is a pronounced asymmetry of surface hopping energies, i.e. a kinetic energy-driven inversion symmetry breaking, whose energy scale is pinned at a significant fraction of the bandwidth. We show, from spin-and angle-resolved photoemission, how this enables surface states of 3d and 4d-based transition-metal oxides to surprisingly develop some of the largest Rashba-like spin splittings that are known. Our findings open new possibilities to produce spin textured states in oxides which exploit the full potential of the bare atomic spin-orbit coupling, raising exciting prospects for oxide spintronics. More generally, the core structural building blocks which enable this are common to numerous materials, providing the prospect of enhanced inversion symmetry breaking at judiciously-chosen surfaces of a plethora of compounds, and suggesting routes to interfacial control of inversion symmetry breaking in designer heterostructures.The lifting of inversion symmetry is a key prerequisite for stabilising a wide range of striking physical properties such as chiral magnetism, ferroelectricity, odd-parity multipolar orders, and the creation of Weyl fermions and other spin-split electronic states without magnetism [1][2][3][4][5][6][7] . Inversion symmetry is naturally broken at surfaces and interfaces of materials, opening exciting routes to stabilise electronic structures distinct from those of the bulk [8][9][10][11][12][13][14][15] . A striking example is found in materials which also host significant spin-orbit interactions, where inversion symmetry breaking (ISB) underpins the formation of topologically-protected surface states 11,16 and Rashba 10,17 spin splitting of surface or interfacelocalised two-dimensional electron gases 14,15,[18][19][20][21][22] , generically characterised by a locking of the quasiparticle spin perpendicular to its momentum. Such effects lie at the heart of a variety of proposed applications in spin-based electronics 10,[23][24][25][26][27] , and provide new routes to stabilise novel physical regimes such as spiral RKKY interactions, enhanced electron-phonon coupling, localisation by a weak potential, large spin-transfer torques, and mixed singlet-triplet superconductivity [28][29][30][31][32][33][34][35] . Conventional wisdom about how to maximize the Rashba effect has been to work with heavy elements whose atomic spin-orbit coupling is large. However, the energetic spin splittings obtained are usually only a small fraction of the atomic spin-orbit energy scale. This is because the key physics is not exclusively that of spi...

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“…However, in real materials, the assumption can be usually broken because the SO coupling mixes different states with different orbitals and orthogonal spinors in a quasiparticle eigenstate [6][7][8]. The SO entanglement can permit the spin-flip electron backscattering [9] and moreover orbital mixing in the eigenstate can play a significant role in an emergence of the large spin-splitting [10][11][12][13][14]. Therefore, it is essentially important to experimentally explore the SO coupling not only in the lifting spin degeneracy but also in the spin and orbital wavefunction as eigenstates.…”

Section: Pacs Numbersmentioning

confidence: 99%

Direct mapping of spin and orbital entangled wave functions under interband spin-orbit coupling of giant Rashba spin-split surface states

et al. 2017

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We use spin-and angle-resolved photoemission spectroscopy (SARPES) combined with polarization-variable laser and investigate the spin-orbit coupling effect under interband hybridization of Rashba spin-split states for the surface alloys Bi/Ag(111) and Bi/Cu(111). In addition to the conventional band mapping of photoemission for Rashba spin-splitting, the different orbital and spin parts of the surface wavefucntion are directly imaged into energy-momentum space. It is unambiguously revealed that the interband spin-orbit coupling modifies the spin and orbital character of the Rashba surface states leading to the enriched spin-orbital entanglement and the pronounced momentum dependence of the spin-polarization. The hybridization thus strongly deviates the spin and orbital characters from the standard Rashba model. The complex spin texture under interband spin-orbit hybridyzation proposed by first-principles calculation is experimentally unraveled by SARPES with a combination of p-and s-polarized light. PACS numbers:A realization of functional capabilities to generate spinsplitting of electronic states without any external magnetic field is a key subject in the research of spintronics [1]. A promising strategy exploits the influence of spin-orbit (SO) interaction that can give rise to the lifting of spin degeneracy under broken space inversion symmetry, the so-called Rashba effect [2]. In the conventional Rashba model, an eigenstate of the SO-induced spin-splitting is treated with an assumption of a pure spin state fully chiral spin-polarized which protects electrons from backscattering [2][3][4][5]. However, in real materials, the assumption can be usually broken because the SO coupling mixes different states with different orbitals and orthogonal spinors in a quasiparticle eigenstate [6][7][8]. The SO entanglement can permit the spin-flip electron backscattering [9] and moreover orbital mixing in the eigenstate can play a significant role in an emergence of the large spin-splitting [10][11][12][13][14]. Therefore, it is essentially important to experimentally explore the SO coupling not only in the lifting spin degeneracy but also in the spin and orbital wavefunction as eigenstates.Beyond the conventional Rashba model, a well-ordered surface alloy BiAg 2 grown on Ag(111) provides an ideal case to study the SO entanglement in Rashba surface states. In the surface alloy, an occupied sp z -like band and a mostly unoccupied p xy -like band show significant Rashba spin splitting [15,16] and cross each other at the specific k || [17][18][19] as shown in Fig. 1 (b). In particular, density functional theory (DFT) calculations showed the strong SO entanglement [8,9] and predicted the complex spin texture that is significantly different from the conventional Rashba model; the sp z band switches spinpolarization at the crossing through SO-induced interband hybridization [19] which is in contrast to the similar system BiCu 2 /Cu(111) as shown in Fig. 1 (b) [14,20,21]. While the presence of the spin-polarized electronic bands ...

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Microscopic mechanism for the Rashba spin-band splitting: Perspective from formation of local orbital angular momentum

Cited by 32 publications

References 37 publications

Physical properties of noncentrosymmetric tungsten and molybdenum aluminides

Physical properties of noncentrosymmetric tungsten and molybdenum aluminides

Maximal Rashba-like spin splitting via kinetic-energy-coupled inversion-symmetry breaking

Direct mapping of spin and orbital entangled wave functions under interband spin-orbit coupling of giant Rashba spin-split surface states

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