Spintronics is aimed at active controlling and manipulating the spin degrees of freedom in semiconductor devices. A promising way to achieve this goal is to make use of the tunable Rashba effect that relies on the spin-orbit interaction (SOI) in a two-dimensional (2D) electron system immersed in an inversion-asymmetric environment. The SOI induced spin-splitting of the 2D-electron state provides a basis for many theoretically proposed spintronic devices. However, the lack of semiconductors with large Rashba effect hinders realization of these devices in actual practice. Here we report on a giant Rashba-type spin splitting in 2D electron systems which reside at tellurium-terminated surfaces of bismuth tellurohalides. Among these semiconductors, BiTeCl stands out for its isotropic metallic surface-state band with the Gamma-point energy lying deep inside the bulk band gap. The giant spin-splitting of this band ensures a substantial spin asymmetry of the inelastic mean free path of quasiparticles with different spin orientations.
We report on many-body corrections to one-electron energy spectra of bulk bismuth tellurohalides---materials that exhibit a giant Rashba-type spin splitting of the band-gap edge states. We show that the corrections obtained in the one-shot $GW$ approximation noticeably modify the spin-orbit-induced spin splitting evaluated within density functional theory. We demonstrate that taking into account many-body effects is crucial to interpret the available experimental data.
The polarization and piezoelectric response of the BiTe$X$ ($X$=Cl, Br, and I) layered tellurohalides are computed from first principles. The results confirm a mixed ionic-covalent character of the bonding, and demonstrate that the internal structure within each triple layer is only weakly affected by the external stress, while the changes in the charge distribution with stress produce a substantial negative piezoelectric response. This suggests a new mechanism for negative piezoelectric response that should remain robust even in ultra-thin film form in this class of materials.
We study the temperature dependence of the Rashba-split bands in the bismuth tellurohalides BiTe$X$ $(X=$ I, Br, Cl) from first principles. We find that increasing temperature reduces the Rashba splitting, with the largest effect observed in BiTeI with a reduction of the Rashba parameter of $40$% when temperature increases from $0$ K to $300$ K. These results highlight the inadequacy of previous interpretations of the observed Rashba splitting in terms of static-lattice calculations alone. Notably, we find the opposite trend, a strengthening of the Rashba splitting with rising temperature, in …
We investigate the electronic structure, dielectric and optical properties of bismuth tellurohalides BiTeX (X = I, Cl, Br) by means of all-electron density functional theory. In particular, we present the ab initio conductivities and dielectric tensors calculated over a wide frequency range, and compare our results with the recent measurements by Akrap et al. , Makhnev et al. , and Rusinov et al. . We show how the low-frequency branch of the optical conductivity can be used to identify characteristic intra- and interband transitions between the Rashba spin-split bands in all three bismuth tell…
We study the possibility of pressure-induced transitions from a normal semiconductor to a topological insulator (TI) in bismuth tellurohalides using density functional theory and tight-binding method. In BiTeI this transition is realized through the formation of an intermediate phase, a Weyl semimetal, that leads to modification of surface state dispersions. In the topologically trivial phase, the surface states exhibit a Bychkov-Rashba type dispersion. The Weyl semimetal phase exists in a narrow pressure interval of 0.2 GPa. After the Weyl semimetal--TI transition occurs, the surface electron…
We performed density functional calculations for ultra-thin bismuth surface alloys: surface alloys of bismuth and face-centered cubic metals Bi/$M$(111)-$(\sqrt{3}\times\sqrt{3})R30°$ ($M$=Cu, Ag, Au, Ni, Co, and Fe). Our calculated Rashba parameters for the Bi/Ag are consistent with the previous experimental and theoretical results. We predicted a trend in the Rashba coefficients $α_R$ of bands around the Fermi energy for noble metals as follows: Bi/Ag > Bi/Cu > Bi/Au. As for the transition metals, there is a trend in $α_R$: Bi/Ni > Bi/Co > Bi/Fe. Our finding may lead to design efficient spin…
Layered non-centrosymmetric bismuth tellurohalides are being examined as candidates for topological insulators. Pressure is believed to be essential for inducing and tuning topological order in these systems. Through electrical transport and Raman scattering measurements, we find superconductivity in two high-pressure phases of BiTeCl with the different normal state features, carrier characteristics, and upper critical field behaviors. Superconductivity emerges when the resistivity maximum or charge density wave is suppressed by the applied pressure and then persists till the highest pressure …
Spin-split Rashba bands have been exploited to efficiently control the spin degree of freedom of moving electrons, which possesses a great potential in frontier applications of designing spintronic devices and processing spin-based information. Given that intrinsic breaking of inversion symmetry and sizeable spin-orbit interaction, two-dimensional (2D) surface alloys formed by heavy metal elements exhibit a pronounced Rashba-type spin splitting of the surface states. Here, we have revealed the essential role of atomic orbital symmetry in the hexagonally warped Rashba spin-split surface state o…
We investigate the bismuth (111) surface by means of time and angle resolved photoelectron spectroscopy. The parallel detection of the surface states below and above the Fermi level reveals a giant anisotropy of the Spin-Orbit (SO) spitting. These strong deviations from the Rashba-like coupling cannot be treated in $\textbf{k}\cdot \textbf{p}$ perturbation theory. Instead, first principle calculations could accurately reproduce the experimental dispersion of the electronic states. Our analysis shows that the giant anisotropy of the SO splitting is due to a large out-of plane buckling of the sp…
In systems with broken inversion symmetry spin-orbit coupling (SOC) yields a Rashba-type spin splitting of electronic states, manifested in a k-dependent splitting of the bands. While most research had previously focused on 2D electron systems, recently a three-dimensional (3D) form of such Rashba-effect was found in a series of bismuth tellurohalides. Whereas these materials exhibit a very large spin-splitting, they lack an important property concerning functionalization, namely the possibility to switch or tune the spin texture. This limitation can be overcome in a new class of functional ma…
Spin- and Angle-resolved Photoelectron Spectroscopy Study of the Quantum Spin Hall Insulator Bismuthene and its Precursor Phase
Chemnitz University of Technology（开姆尼茨工业大学）；Research Center for Materials, Architectures and Integration of Nanomembranes (MAIN)（纳米膜材料、架构与集成研究中心）；MAX IV Laboratory（MAX IV 实验室）；Lund University（隆德大学）
In transition metal perovskites (ABO3) most physical properties are tunable by structural parameters such as the rotation of the BO6 octahedra. Examples include the Néel temperature of orthoferrites, the conductivity of mixed-valence manganites, or the band gap of rare-earth scandates. Since oxides often host large internal electric dipoles and can accommodate heavy elements, they also emerge as prime candidates to display Rashba spin-orbit coupling, through which charge and spin currents may be efficiently interconverted. However, despite a few experimental reports in SrTiO3-based interface s…
The surface spin states for bismuth thin films were investigated using an $sp^3$ tight-binding model. The model explains the experimental observations using angle-resolved photoemission spectroscopy, including the Fermi surface, the band structure with Rashba spin splitting, and the quantum confinement in the energy band gap of the surface states. A large out-of-plane spin component also appears. The surface states penetrate inside the film to within approximately a few bilayers near the Brillouin-zone center, whereas they reach the center of the film near the Brillouin-zone boundary.
Reversible and nonvolatile manipulation of the spin-orbit interaction in ferroelectric field-effect transistors based on a two-dimensional bismuth oxychalcogenide
To realize a one-dimensional (1D) system with strong spin-orbit coupling is a big challenge in modern physics, since the electrons in such a system are predicted to exhibit exotic properties unexpected from the 2D or 3D counterparts, while it was difficult to realize genuine physical properties inherent to the 1D system. We demonstrate the first experimental result that directly determines the purely 1D band structure by performing spin-resolved angle-resolved photoemission spectroscopy of Bi islands on a silicon surface that contains a metallic 1D edge structure with unexpectedly large Rashba…
Large spin splitting at Rashba interface, giving rise to strong spin-momentum locking, is essential for efficient spin-to-charge conversion. Recently, a Cu/Bismuth oxide (Bi2O3) interface has been found to exhibit an efficient spin-to-charge conversion similar to a Ag/Bi interface with large Rashba spin splitting. However, the guiding principle of designing the metal/oxide interface for the efficient conversion has not been clarified yet. Here we report strong non-magnetic (NM) material dependence of spin splitting at NM/Bi2O3 interfaces. We employed spin pumping technique to inject spin curre…
Electron spin takes critical role in almost all novel phenomena discovered in modern condensed matter physics (High-temperature superconductivity, Kondo effect, Giant Magnetoresistance, topological insulator, quantum anomalous Hall effect, etc.). However, the measurements for electron spin is of poor quality which blocks the development of material sciences because of the low efficiency of spin polarimeter. Here we show an imaging type exchange-scattering spin polarimeter with 5 orders more efficiency compared with a classical Mott polarimeter. As a demonstration, the fine spin structure of el…
We have performed a fully relativistic first-principles density functional calculation examining the surface state of bismuth (Bi) (111) multi-layer nanofilm, with up to 20 Bi bilayers, and investigated the Rashba effect and spin texture on the Bi surfaces. We have revealed a giant out-of-plane spin states on the Fermi lines, and the maximum value of the out-of-plane spin component being approximately 40% of the magnitude of the total spin. We have also evaluated the Rashba parameter $α_R \simeq 1.9 {\rm eV}\cdot$Åusing the surface state bands which is buried in the bulk state, at -0.32 eV bel…
