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Controlling electronic processes in low-dimension electron systems is centrally important for both fundamental and applied researches. While most of the previous works focused on SrTiO 3 -based two-dimensional electron gases (2DEGs), here we report on a comprehensive investigation in this regard for amorphous-LaAlO 3 / KTaO 3 2DEGs with the Fermi energy ranging from ∼13 meV to ∼488 meV. The most important observation is the dramatic variation of the Rashba spin−orbit coupling (SOC) as Fermi energy sweeps through 313 meV: The SOC effective field first jumps and then drops, leading to a cusp of ∼2.6 T. Above 313 meV, an additional species of mobile electrons emerges, with a 50-fold enhanced Hall mobility. A relationship between spin relaxation distance and the degree of band filling has been established in a wide range. It indicates that the maximal spin precession length is ∼70.1 nm and the maximal Rashba spin splitting energy is ∼30 meV. Both values are much larger than the previously reported ones. As evidenced by density functional theory calculation, these unusual phenomena are closely related to the distinct band structure of the 2DEGs composed of 5d electrons. The present work further deepens our understanding of perovskite conducting interfaces, particularly those composed of 5d transition-metal oxides.

Two-dimensional electron gas (2DEG) at the perovskite oxide interface exhibits a lot of exotic properties, presenting a promising platform for the exploration of emergent phenomena. While most of the previous works focused on SrTiO-based 2DEG, here we report on the fabrication of high-quality 2DEGs by growing an amorphous LaAlO layer on a (001)-orientated KTaO substrate, which is a 5d metal oxide with a polar surface, at a high temperature that is usually adopted for crystalline LaAlO. Metallic 2DEGs with a Hall mobility as high as ∼2150 cm/(V s) and a sheet carrier density as low as 2 × 10 cm are obtained. For the first time, the gating effect on the transport process is studied, and its influence on spin relaxation and inelastic and elastic scattering is determined. Remarkably, the spin relaxation time can be strongly tuned by a back gate. It is reduced by a factor of ∼69 while the gate voltage is swept from -25 to +100 V. The mechanism that dominates the spin relaxation is elucidated.

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An accurate density-functional method is used to study systematically half-metallic ferromagnetism and stability of zincblende phases of 3d-transition-metal chalcogenides. The zincblende CrTe, CrSe, and VTe phases are found to be excellent half-metallic ferromagnets with large halfmetallic gaps (up to 0.88 eV). They are mechanically stable and approximately 0.31-0.53 eV per formula unit higher in total energy than the corresponding nickel-arsenide ground-state phases, and therefore would be grown epitaxially in the form of films and layers thick enough for spintronic applications.PACS numbers: 75.90.+w, 62.25.+g, 73.22.-f, 75.30.-m Phys Rev Lett 91, 037204 (2003) Half-metallic ferromagnets are seen as a key ingredient in future high performance spintronic devices, because they have only one electronic spin channel at the Fermi energy and, therefore, may show nearly 100 % spin polarization [1,2]. Since de Groot et al's discovery [3] in 1983, a lot of half-metallic ferromagnets have been theoretically predicted and some of them furthermore have been confirmed experimentally [4,5,6,7]. Much attention has been paid to understanding the mechanism behind the half-metallic magnetism and to studying its implication on various physical properties [8,9]. However, it is highly desirable to explore new halfmetallic ferromagnetic materials which are compatible with important III-V and II-VI semiconductors. For this purpose, effort has be made on the metastable zincblende (B3) phases such as the transition-metal pnictides [10,11,12,13,14,15,16,17,18,19,20]. Although zincblende phases of MnAs [11], CrAs [12,13] and CrSb [14] have been successfully fabricated as nanodots, ultrathin films and ultrathin layers in multilayers, it has not been possible to grow the zincblende half-metallic ferromagnetic phases as high-quality layers or thick films. This is due to the metastable zincblende phases being about 1 eV per formula unit higher in energy than the ground state nickel-arsenide (B8 1 ) phases. However, spintronic devices require thick films or layers. Therefore, it is important to explore theoretically other halfmetallic ferromagnetic materials, which on the one hand are compatible with the binary tetrahedral-coordinated semiconductors, and on the other hand are not only low in energy with respect to the corresponding ground-state structures but also mechanically stable against structural deformations.In this Letter we make use of an accurate fullpotential density-functional method to study systematically transition-metal chalcogenides in the zincblende and nickel-arsenide structures in order to find halfmetallic ferromagnetic phases which could be realized in the form of films and layers thick enough. We shall show that CrTe, CrSe, and VTe in the zincblende structure are excellent half-metallic ferromagnets with wide halfmetallic gaps. They will be proved to be mechanically stable and approximately 0.31-0.53 eV per formula unit higher in energy than the corresponding ground-state phases, and therefore would be grown epitax...

Coexistence of intrinsic ferrovalley (FV) and nontrivial band topology attracts intensive interest both for its fundamental physics and for its potential applications, namely valley-polarized quantum anomalous Hall insulator (VQAHI). Here, based on first-principles calculations by using generalized gradient approximation plus U (GGA+U) approach, the VQAHI induced by electronic correlation or strain can occur in monolayer RuBr2. For perpendicular magnetic anisotropy (PMA), the ferrovalley (FV) to half-valley-metal (HVM) to quantum anomalous Hall (QAH) to HVM to FV transitions can be driven by increasing electron correlation U. However, there are no special QAH states and valley polarization for in-plane magnetic anisotropy. By calculating actual magnetic anisotropy energy (MAE), the VQAHI indeed can exist between two HVM states due to PMA, a unit Chern number/a chiral edge state and spontaneous valley polarization. The increasing U can induce VQAHI, which can be explained by sign-reversible Berry curvature or band inversion between dxy/dx2-y2and dz2orbitals. Even though the real U falls outside the range, the VQAHI can be achieved by strain. Taking U=2.25 eV as a concrete case, the monolayer RuBr2 can change from a common ferromagentic (FM) semiconductor to VQAHI under about 0.985 compressive strain. It is noted that the edge states of VQAHI are chiral-spin-valley locking, which can achieve complete spin and valley polarizations for low-dissipation electronics devices. Both energy band gap and valley splitting of VQAHI in monolayer RuBr2 are higher than the thermal energy of room temperature (25 meV), which is key at room temperature for device applications. It is found that electronic correlation or strain have important effects on Curie temperature of monolayer RuBr2. These results can be readily extended to other monolayer MXY (M = Ru, Os; X/Y=Cl, Br I).

The full-potential augmented plane wave plus local orbital method within density-functional theory is used to predict that MnBi in the zinc-blende structure is a true half-metallic ferromagnet with a magnetic moment of 4.000 B per formula unit. This contrasts with the zinc-blende phase of MnAs, which is only a nearly half-metallic ferromagnet. This half-metallic ferromagnetic behavior of zinc-blende MnBi is found to be robust against compressive volume changes of up to 15%, its stability being enhanced by the relativistic shift of the valence s state energy levels. Zinc-blende MnBi could possibly be grown epitaxially on the important binary semiconductors such as InSb or CdTe, although it remains to be seen whether epitaxially it retains its halfmetallic ferromagnetic state.

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