Giant Ambipolar Rashba Effect in the Semiconductor BiTeI

Abstract

We observe a giant spin-orbit splitting in bulk and surface states of the non-centrosymmetric semiconductor BiTeI. We show that the Fermi level can be placed in the valence or in the conduction band by controlling the surface termination. In both cases it intersects spin-polarized bands, in the corresponding surface depletion and accumulation layers. The momentum splitting of these bands is not affected by adsorbate-induced changes in the surface potential. These findings demonstrate that two properties crucial for enabling semiconductor-based spin electronics -a large, robust spin splitting and ambipolar conduction -are present in this material.

Quantum oscillations and optical conductivity in Rashba spin-splitting BiTeI

“…1 and 6, which assign it to a bulk conduction branch and agrees within 50% with the values from Ref. 8, but for electronic bands assigned to the surface. Moreover, it also agrees within better than 50% with the value of k F for the surface states near the bottom of the conduction band, obtained from band structure calculations 9 .…”

“…Optical spectroscopy of this compound found indeed an electronic excitation spectrum consistent with the splitting of the bulk conduction and valence bands 5 and further photoemission study suggested the 3D nature of these bands 6 . More recent ARPES reports however, indicated the reconstruction of the band structure at the Te (or I) terminated surface and the existence of surface electronic branches, possibly with even larger Rashba spinsplitting 7,8 . On the theoretical side, ab-initio calculations for BiTeX(X=Cl, Br, I) do claim the formation of a surface 2D electron system distinct from the bulk states that has a larger Rashba splitting 9 .…”

Momentum and photon energy dependence of the circular dichroic photoemission in the bulk Rashba semiconductorsBiTeX(X=I, Br, Cl)

“…An additional state, b2, disperses between the two. It is hardly detectable at this photon energy and we attribute it to the outer branch of the three-dimensional bulk-derived spin-split state [9,11]. Fig.…”

“…In the case of BiTeI, the unit cell is formed by the alternation of Bi, Te, and I layers, with P 3m1 point group symmetry. The natural cleavage plane is between Te and I and both terminations are possible [9,37]. In this study we focus only on the electronic properties of the Te-terminated surfaces of all the compounds.…”

“…The need for novel and advanced spintronics devices has stimulated the quest for materials hosting metallic spinpolarized bands embedded in a semiconducting bulk. Starting from the present knowledge on topological insulators (TIs) [1][2][3][4][5], the design of materials with spin-polarized bands requires the tailoring of the spin texture at the Fermi level (E F ), hence the synthesis of systems such as ternary TIs [6,7] or the bulk Rashba semiconductors BiTeX (X = I, Br, Cl) characterized by ambipolar surface states [8][9][10][11][12]. Nowadays one of the major challenges is to study the fully threedimensional spin properties of ternary TIs, and the bulk Rashba semiconductors, as is done for magnetic doped TIs [13].…”