Newtype large Rashba splitting in quantum well states induced by spin chirality in metal/topological insulator heterostructures

Abstract

In a two-dimensional system without inversion symmetry, such as a surface or interface, the potential-asymmetry-induced electric field can create the Rashba effect, which is spin-band splitting caused by spin-orbit coupling (SOC). On the basis of Rashba splitting, several promising spintronic devices, such as the Datta-Das spin transistor, have been designed for manipulating spin precession in the absence of a magnetic field. Rashba splitting can be created in several metal quantum well states (QWSs), such as in Pb/Si; however, the effect is usually moderate because the itinerant carriers within the metal film strongly screen out the electric field. A large Rashba splitting can be found in the unoccupied QWSs of the Bi monolayer on Cu (111); however, the metallic substrate limits the diversity of its applications. To achieve strong Rashba splitting in metal thin film based on an insulating substrate, which is most desirable, we propose the normal metal (NM)/topological insulator (TI) heterostructure for manufacturing Rashba-type splitting in NM QWSs. In such a hybrid system, the TI spin-momentum-locking Dirac surface state associated with SOC strongly modifies the penetration depth of the NM QWS into the TI substrate according to the spin orientation, leading to strong Rashba-type splittings in the NM QWS. Combining ab initio calculations and analytical modeling, the momentum separation of the Rashba splitting in the NM QWS can be as large as 0.18 Å − 1 , which is the largest ever found in metal-film/non-metallic substrate systems. Furthermore, the induced spin polarization in the Rashba band is nearly 100%, much higher than the typical value of 40-50% in the TI surface state itself. This remarkably large Rashba splitting and the high spin polarization in the NM QWS evoked by the spin chirality of the TI surface state confer great potential for the development of spintronic devices. INTRODUCTIONOne of the major tasks in the development of semiconductor spintronics is finding a material with remarkable Rashba-type splitting to control the spin current. For example, the Datta-Das spin transistor, 1 proposed for more than 20 years, switches the spin current by controlling the magnitude of Rashba splitting of a two-dimensional electron gas in a semiconductor heterostructure. [2][3][4][5][6] After decades of trials, the Datta-Das spin transistor has finally been experimentally realized recently. 7 However, the mild splitting of the two-dimensional electron gas bands is inapplicable for spin transistors working at room temperature or designed in the nanoscale. 7-9 A much more feasible approach is thus highly desirable.Alternatively, giant Rashba splittings can be found in the surface state (SS) of noble-metal-based surface alloys with strong spin-orbit couplings (SOCs) in heavy atoms. 10,11 The interatomic electric field at the surface-alloy plane is the key to the giant splitting. 12 Regarding the influence of the metal host, the SS would be hidden in the spintronics functions; therefore, efforts have been made on s...

Chemical Instability of an Interface between Silver and Bi2Se3 Topological Insulator at Room Temperature

“…Many innovative technical solutions have been proposed based on the Bi 2 Se 3 topological insulator interfaced with metal Ag as an electrode, functional layer, or cocatalyst. ,,, All these initial investigations do not take in account aging of the systems due to possible chemical changes on the interfaces. They might identify the presence of Ag immediately after the synthesis but do not repeat the same analysis after some time has passed to confirm the chemical stability of the interface.…”

“…Some theoretical papers, involving the metal/TI systems, − have recently been published, while experimental studies are very rare. Mostly they focus on systems with extremely low coverage, that is, quasi-isolated metal atoms adsorbed on a TI surface. , Only recently Walsh et al have published the first systematic research on Au, Pd, Ir, and some transition metals interfaced with Bi 2 Se 3 .…”

“…In a theoretical work by Xiao et al, where a focus was on catalytic properties of metal clusters on Bi 2 Se 3 , Ag was modeled as stable clusters consisting of seven atoms. In the work of Chang et al, which focused on a new type of Rashba splitting at the metal/TI interface, Ag was modeled as an epitaxial overlayer. However, no experimental evidence of what happens when Ag is deposited on Bi 2 Se 3 has been reported.…”

Growth, morphology and stability of Au in contact with the Bi2Se3(0 0 0 1) surface

“…These calculations showed that for Au and graphene the spin-momentum locking is maintained for the TSS [6], while Pd and Pt should exert a stronger interaction with the TI surface resulting in delocalization of the TSS and poor spin-momentum locking. In another study, a theory predicts that Ag and Au thin layers on Bi2Se3 have large Rashba splitting and high spin polarization of the Ag quantum wells, which give a great potential for development of spintronic devices [7]. Finally, calculations foresee also that the presence of robust TSS affect the adsorption properties of metals (bi-layer of Au, and clusters of Au, Ag, Cu, Pt, and Pd) supported on TI [8] [9], in some cases resulting in the enhancement of the catalytic processes.…”

Efficient charge-spin conversion and magnetization switching through the Rashba effect at topological-insulator/Ag interfaces

“…However, recent ARPES measurements reveal that the strength of Rashba splitting on the three-dimensional (3D) TI, Bi2Se3, surface can be tuned by involving adsorbates, such as Pd and Cs [19,21]. Moreover, a recent theoretical work suggests that a new kind of large Rashba splitting states is expected to appear particularly at the Bi2Se3/Ag interface induced by the spin chirality of TSSs, which possess stronger spin polarizations than TSS in Bi2Se3 [27]. Therefore, this emerging RSS are promising to generate spin currents more efficiently.…”