High-performance Bi(2)Te(3)-based topological insulator film magnetic field detector

Formation of BixSey Phases Upon Annealing of the Topological Insulator Bi2Se3: Stabilization of In-Depth Bismuth Bilayers

The goal of this work is to study transformations that occur upon heating Bi₂Se₃ to temperatures up to 623 K. X-ray diffraction (XRD) and scanning tunneling microscopy (STM) and spectroscopy (STS) techniques were used in our investigation. XRD was measured following the 00L and 01L truncation rods. These measurements revealed that upon heating there is a coexistence of a major Bi₂Se₃ phase and other ones that present structures of quintuple-layers intercalated with Bismuth bilayers. STM measurements of the surface of this material showed the presence of large hexagonal Bi_xSe_y domains embedded in a Bi₂Se₃ matrix. STS experiments were employed to map the local electronic density of states and characterize the modifications imposed by the presence of the additional phases. Finally, density functional theory (DFT) calculations were performed to support these findings.

Heterostructured ferromagnet–topological insulator with dual-phase magnetic properties

The introduction of ferromagnetism at the surface of a topological insulator (TI) produces fascinating spin-charge phenomena. It has been assumed that these fascinating effects are associated with a homogeneous ferromagnetic (FM) layer possessing a single type of magnetic phase. However, we obtained phase separation within the FM layer of a Ni₈₀Fe₂₀/Bi₂Se₃ heterostructure. This phase separation was caused by the diffusion of Ni into Bi₂Se₃, forming a ternary magnetic phase of Ni:Bi₂Se₃. The inward diffusion of Ni led to the formation of an FeSe phase outward, transforming the original Ni₈₀Fe₂₀/Bi₂Se₃ into a sandwich structure comprising FeSe/Ni:Bi₂Se₃/Bi₂Se₃ with dual-phase magnetic characteristics similar to that driven by the proximity effect. Such a phenomenon might have been overlooked in previous studies with a strong focus on the proximity effect. X-ray magnetic spectroscopy revealed that FeSe and Ni:Bi₂Se₃ possess horizontal and perpendicular magnetic anisotropy, respectively. The overall magnetic order of the heterostructure can be easily tuned by adjusting the thickness of the Bi₂Se₃ as it compromises the magnetic orders of the two magnetic phases. This discovery is essential to the quantification of spin-charge phenomena in similar material combinations where the FM layer is composed of multiple elements.

In this study we visualized thermodynamically stable chalcogen compounds in the vicinity of a Py/Bi₂Se₃ interface with dual magnetic order due to a phase separation effect.

Anomalous photoelectric effect of a polycrystalline topological insulator film

A topological insulator represents a new state of quantum matter that possesses an insulating bulk band gap as well as a spin-momentum-locked Dirac cone on the surface that is protected by time-reversal symmetry. Photon-dressed surface states and light-induced surface photocurrents have been observed in topological insulators. Here, we report experimental observations of an anomalous photoelectric effect in thin films of Bi₂Te₃, a polycrystalline topological insulator. Under illumination with non-polarised light, transport measurements reveal that the resistance of the topological surface states suddenly increases when the polycrystalline film is illuminated. The resistance variation is positively dependent on the light intensity but has no relation to the applied electric field; this finding can be attributed to the gap opening of the surface Dirac cone. This observation of an anomalous photoelectric effect in polycrystalline topological insulators offers exciting opportunities for the creation of photodetectors with an unusually broad spectral range. Moreover, polycrystalline topological insulator films provide an attractive material platform for exploring the nature and practical application of topological insulators.