The quantum anomalous Hall effect (QAHE) has recently been reported to emerge in magnetically-doped topological insulators. Although its general phenomenology is well established, the microscopic ...origin is far from being properly understood and controlled. Here we report on a detailed and systematic investigation of transition-metal (TM)-doped Sb\(_2\)Te\(_3\). By combining density functional theory (DFT) calculations with complementary experimental techniques, i.e., scanning tunneling microscopy (STM), resonant photoemission (resPES), and x-ray magnetic circular dichroism (XMCD), we provide a complete spectroscopic characterization of both electronic and magnetic properties. Our results reveal that the TM dopants not only affect the magnetic state of the host material, but also significantly alter the electronic structure by generating impurity-derived energy bands. Our findings demonstrate the existence of a delicate interplay between electronic and magnetic properties in TM-doped TIs. In particular, we find that the fate of the topological surface states critically depends on the specific character of the TM impurity: while V- and Fe-doped Sb\(_2\)Te\(_3\) display resonant impurity states in the vicinity of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The single-ion magnetic anisotropy energy and easy axis, which control the magnetic gap opening and its stability, are also found to be strongly TM impurity-dependent and can vary from in-plane to out-of-plane depending on the impurity and its distance from the surface. Overall, our results provide general guidelines for the realization of a robust QAHE in TM-doped Sb\(_2\)Te\(_3\) in the ferromagnetic state.
High optical quality GaSe samples with faces parallel and orthogonal to the optical axis are manufactured. o-and e-wave dispersions are studied by THz time domain spectroscopy. New dispersion ...equations are designed that are suitable for application in the entire transparency range from the near IR through the mid-IR and further into the THz.
A dense set of solid solution crystals GaSe 1-x S x is examined using THz-TDS. Evolution of phonon absorption peaks with the increase of S content is shown to have complex transformation, which ...should be considered in the design of dispersion equations for THz applications.
Hybrid organic/inorganic interfaces have been widely reported to host emergent properties that go beyond those of their single constituents. Coupling molecules to the recently discovered topological ...insulators, which possess a linearly dispersing and spin-momentum--locked Dirac fermions, may offer a promising platform towards new functionalities. Here, we report a scanning tunneling microscopy and spectroscopy study of the prototypical interface between MnPc molecules and a Bi\(_2\)Te\(_3\) surface. MnPc is found to bind stably to the substrate through its central Mn atom. The adsorption process is only accompanied with a minor charge transfer across the interface, resulting in a moderately n-doped Bi\(_2\)Te\(_3\) surface. More remarkably, topological states remain completely unaffected by the presence of the molecules, as evidenced by the absence of scattering patterns around adsorption sites. Interestingly, we show that, while the HOMO and LUMO orbitals closely resembles those of MnPc in the gas phase, a new hybrid states emerges through interaction with the substrate. Our results pave the way towards hybrid organic--topological insulator heterostructures, which may unveil a broad range of exciting and unknown phenomena.
Meeting of non-trivial topology with magnetism results in novel phases of matter, such as Quantum Anomalous Hall (QAH) or axion insulator phases. Even more exotic states with high and tunable Chern ...numbers are expected at the contact of intrinsic magnetic topological insulators (IMTIs) and 2D topological insulators (TIs). Here we synthesize a heterostructures composed of 2D TI and 3D IMTIs, specifically of bismuth bilayer on top of MnBi2Te4-family of compounds and study their electronic properties by means of angle-resolved photoelectron spectroscopy (ARPES) and density functional theory (DFT). The epitaxial interface is characterized by hybridized Bi and IMTI electronic states. The Bi bilayer-derived states on different members of MnBi2Te4-family of materials are similar, except in the region of mixing with the topological surface states of the substrate. In that region, the new, substrate dependent interface Dirac state is observed. Our ab initio calculations show rich interface phases with emergence of exchange split 1D edge states, making the Bi/IMTI heterostructures promising playground for observation of novel members in the family of quantum Hall effects.
The authors present the results of a comparative study of the immunogenicity of the living (Sm-d) and killed E. coli vaccine which, in determination by such methods as the Vidal test, passive ...hemagglutination test, bactericidal activity, establishment of passive and active defence, proved to be the same in both vaccines. However, with the aid of Rauss and Ketyi's method, modified by the authors (determination of nonsuceptibility in enteral infection of the animals with intestine sterilized with streptomycin) it was possible to reveal the capacity of the living vaccine to depress the growth and the activity (reproducible and statistically controlled) of E. coli administered into the organism of the immunized animal for the purpose of infection. They were discharged with the feces for a definite period in 90% of control animals and mice immunized with the killed vaccine; this occured in less than 10% of the animals immunized with the living vaccine.
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