Zhiyi Chen

Singular robust room-temperature spin response from topological Dirac fermions

Topological insulators are a class of solids in which the non-trivial inverted bulk band structure gives rise to metallic surface states that are robust against impurity scattering. In three-dimensional (3D) topological insulators, however, the surface Dirac fermions intermix with the conducting bulk, thereby complicating access to the low-energy (Dirac point) charge transport or magnetic response. Here we use differential magnetometry to probe spin rotation in the 3D topological material family (Bi2Se3, Bi2Te3 and Sb2Te3). We report a paramagnetic singularity in the magnetic susceptibility at low magnetic fields that persists up to room temperature, and which we demonstrate to arise from the surfaces of the samples. The singularity is universal to the entire family, largely independent of the bulk carrier density, and consistent with the existence of electronic states near the spin-degenerate Dirac point of the 2D helical metal. The exceptional thermal stability of the signal points to an intrinsic surface cooling process, probably of thermoelectric origin, and establishes a sustainable platform for the singular field-tunable Dirac spin response.

Molecular Beam Epitaxial Growth and Properties of Bi2Se3 Topological Insulator Layers on Different Substrate Surfaces

Growth of high-quality Bi2Se3 films is crucial not only for study of topological insulators but also for manufacture of technologically important materials. We report a study of the heteroepitaxy of single-crystal Bi2Se3 thin films grown on GaAs and InP substrates by use of molecular beam epitaxy. Surface topography, crystal structure, and electrical transport properties of these Bi2Se3 epitaxial films are indicative of highly c-axis oriented films with atomically sharp interfaces.

Molecular beam epitaxial growth and characterization of Bi2Se3/II-VI semiconductor heterostructures

Surfaces of three-dimensional topological insulators (TIs) have been proposed to host quantum phases at the interfaces with other types of materials, provided that the topological properties of interfacial regions remain unperturbed. Here, we report on the molecular beam epitaxy growth of II-VI semiconductor–TI heterostructures using c-plane sapphire substrates. Our studies demonstrate that Zn0.49Cd0.51Se and Zn0.23Cd0.25Mg0.52Se layers have improved quality relative to ZnSe. The structures exhibit a large relative upward shift of the TI bulk quantum levels when the TI layers are very thin (∼6nm), consistent with quantum confinement imposed by the wide bandgap II-VI layers. Our transport measurements show that the characteristic topological signatures of the Bi2Se3 layers are preserved.

Surface plasmon polaritons in topological insulator nano-films and superlattices

We investigate the propagation of surface plasmon polaritons (SPPs) in thin films of topological insulators. Cases of single films and multilayered stacks are analyzed. The materials considered are second generation three dimensional topological insulators Bi2Se3, Bi2Te3, and Sb2Te3. Dispersion relations and propagation lengths of SPPs are estimated numerically, taking into account the variation of bulk dielectric functions of topological insulators, as well as substrate, using the Drude-Lorentz model. The key factors affecting propagation length are identified and experimental modifications for tuning the dispersion relations are proposed. The apparent discrepancy between the experimental data and previously considered theory is resolved.The propagation of surface plasmon polaritons in thin films of topological insulators is studied. The materials considered are second generation three dimensional topological insulators Bi

Stable topological insulators achieved using high energy electron beams.

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Emergent surface superconductivity in the topological insulator Sb2Te3.

Se

Robust Topological Interfaces and Charge Transfer in Epitaxial Bi2Se3/II–VI Semiconductor Superlattices

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Corrigendum: Singular robust room-temperature spin response from topological Dirac fermions

, Bi

Carrier tuned magnetism in topological insulator Mn:Bi 2 Te 3

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Disorder-induced dimensionality transition and non-local transport in Sb

Te