Observation of huge surface hole mobility in the topological insulator Bi(0.91)Sb(0.09) (111)

Bismuth-based liquid metals: advances, applications, and prospects

Bismuth-based liquid metals (LMs) are a large group of alloys with melting points slightly above room temperature. They are associated with fewer encapsulation constraints than room temperature LMs such as mercury, sodium-potassium alloys, and gallium-based alloys and are more likely to remain stable in the natural environment. In addition, their low melting point properties enable them to soften and melt via easy control. Bismuth-based alloys can also be modified with metal-based, carbon-based, and ceramic-based micro/nano particles as well as polymeric materials to create a series of novel composites owing to their outstanding functions. Based on these considerations, this review provides a comprehensive overview of bismuth-based LMs. The categories of bismuth and bismuth-based LMs are first briefly introduced to better systematize the physical and chemical properties of bismuth-based LMs. Based on these properties, bismuth-based LMs have been prepared using various methods, and this review briefly categorizes these preparation methods based on their finished forms (lumps, powders, and films). In addition, this review details the research progress of bismuth-based LMs in the fields of printed electronics, 3D printing, thermal management, biomedicine, chemical engineering, and deformable robotics. Finally, the challenges and future opportunities of bismuth-based LMs in the development process are discussed and visualized from different perspectives.

Integration of the Rhombohedral BiSb(0001) Topological Insulator on a Cubic GaAs(001) Substrate

Bismuth-antimony alloy (Bi_1 - xSb_x) is the first reported 3D topological insulator (TI). Among many TIs reported to date, it remains the most promising for spintronic applications thanks to its large conductivity, its colossal spin Hall angle, and the possibility to build low-current spin-orbit-torque magnetoresistive random access memories. Nevertheless, the 2D integration of TIs on industrial standards is lacking. In this work, we report the integration of high-quality rhombohedral BiSb(0001) topological insulators on a cubic GaAs(001) substrate. We demonstrate a clear epitaxial relationship at the interface, a fully relaxed TI layer, and the growth of a rhombohedral matrix on top of the cubic substrate. The antimony composition of the Bi_1 - xSb_x layer is perfectly controlled and covers almost the whole TI window. For optimized growth conditions, the sample generates a semiconductor band structure at room temperature in the bulk and exhibits metallic surface states at 77 K.

Onset of a Two-Dimensional Superconducting Phase in a Topological-Insulator-Normal-Metal Bi_{1-x}Sb_{x}/Pt Junction Fabricated by Ion-Beam Techniques

Inducing superconductivity in a topological insulator can lead to novel quantum effects. However, experimental approaches to turn a topological insulator into a superconductor are limited. Here, we report on superconductivity in topological insulator Bi_{0.91}Sb_{0.09} induced via focused ion-beam deposition of a Pt thin film. The superconducting phase exhibits a Berezinski-Kosterlitz-Thouless transition, demonstrative of its two-dimensional character. From the in-plane upper critical field measurements, we estimate the superconducting thickness to be ∼17  nm for a 5.5-μm-thick sample. Our results provide evidence that the interface superconductivity could originate from the surface states of Bi_{0.91}Sb_{0.09}.

Investigation of novel crystal structures of Bi-Sb binaries predicted using the minima hopping method

Semi-conducting alloys Bi_xSb_1-x have emerged as a potential candidate for topological insulators and are well known for their novel thermoelectric properties. In this work, we present a systematic study of the low-energy phases of 35 different compositions of Bi_xSb_1-x (0 < x < 1) at zero temperature and zero pressure. We explore the potential energy surface of Bi_xSb_1-x as a function of Sb concentration by using the ab initio minima hopping structural search method. Even though Bi and Sb crystallize in the same R3[combining macron]m space group, our calculations indicate that Bi_xSb_1-x alloys can have several other thermodynamically stable crystal structures. In addition to the configurations on the convex hull, we find a large number of metastable structures which are dynamically stable. The electronic band structure calculations of several stable phases reveal the presence of strong spin-orbit interaction leading to the Rashba-Dresselhaus spin-splitting of bands which is of great interest for spintronics applications. We also find an orthorhombic structure of BiSb in the Imm2 space group which exhibits signatures of type-II Weyl semimetal. Additionally, we have studied the thermoelectric properties of the selected structures. Regarding thermoelectric properties, we find that the compositions which crystallize in the rhombohedral structure exhibit values of the Seebeck coefficient and the power factor similar to that of Bi₂Te₃ at room temperature, while the theoretical maximum figure of merit (Z_eT) is smaller than that of Bi₂Te₃. We observe enhancement in the thermopower with the increase in the strength of the Rashba-Dresselhaus spin-splitting effect.

Bulk-Induced 1/f Noise at the Surface of Three-Dimensional Topological Insulators

Slow intrinsic fluctuations of resistance, also known as the flicker noise or 1/f-noise, in the surface transport of strong topological insulators (TIs) is a poorly understood phenomenon. Here, we have systematically explored the 1/f-noise in field-effect transistors (FET) of mechanically exfoliated Bi1.6Sb0.4Te2Se TI films when transport occurs predominantly via the surface states. We find that the slow kinetics of the charge disorder within the bulk of the TI induces mobility fluctuations at the surface, providing a new source of intrinsic 1/f-noise that is unique to bulk TI systems. At small channel thickness, the noise magnitude can be extremely small, corresponding to the phenomenological Hooge parameter γH as low as ≈10(-4), but it increases rapidly when channel thickness exceeds ∼1 μm. From the temperature (T)-dependence of noise, which displayed sharp peaks at characteristic values of T, we identified generation-recombination processes from interband transitions within the TI bulk as the dominant source of the mobility fluctuations in surface transport. Our experiment not only establishes an intrinsic microscopic origin of noise in TI surface channels, but also reveals a unique spectroscopic information on the impurity bands that can be useful in bulk TI systems in general.