Such a problem has not been emphasized and studied in SmB 6 nanowires. If Ni, the most popular catalyst assisting the growth of boride nanowire, migrates along the nanowire surface, the time reversal symmetry in topological Kondo insulator SmB 6 can be broken. Nonetheless, the influence of surface impurity on topological insulator cannot be ignored simply. Since the transport of semiconductor nanowire is mainly decided by the bulk of nanowire, the occasional distribution of trace amount of catalyst on nanowire sidewall is rarely considered in the study of semiconductor nanowire. High resolution transmission electron microscopy (HRTEM) have observed gold or aluminum catalyst on the surface of Si nanowires. However, VLS growth has an intrinsic disadvantage, which is the possible migration of catalyst along the nanowire sidewall during the nanowire growth under some conditions. Vapor-liquid-solid (VLS) mechanism is usually employed to explain the growth of SmB 6 nanowires with the help of catalyst. SmB 6 nanowires are usually prepared by chemical vapor deposition (CVD) with metal catalyst, e.g., Ni and Pd. In another experiment without catalyst on the substrate, rarely growth of SmB 6 nanowire is found.
However, the surface of SmB 6 nanowires prepared in this way is covered by a layer with the thickness of ~10 nm, which is not suitable to evaluate their surface conduction. SmB 6 nanowires have been synthesized by heating Sm with BCl 3 in the ambient of H 2 and Ar. In order to further understand the relation between novel physical phenomena and the surface of SmB 6 nanowires, more investigation of the growth of SmB 6 nanowires is highly desirable. The exposed surface of SmB 6 nanowire seems to show more novel behavior than that of the bulk crystal. A size-dependent surface magnetism is concluded in thin SmB 6 nanowire independent of the strong correlations and spin-orbit interactions. report strong surface magnetism and hysteretic magnetoresistance in thin SmB 6 nanowires. For example, higher aspect ratio is proposed to be the reason for bigger activation energy in SmB 6 nanobelt. One-dimensional SmB 6 nanostructure is suitable to investigate the physical phenomenon relating to the surface due to its large aspect ratio. Magnetotransport measurement have revealed topological insulator properties in SmB 6, such as spin-polarized surface state transport and linear positive magnetoresistance at low field. SmB 6 is a well-known Kondo insulator and has been identified as a prototype of topological Kondo insulator.
Theoretical and experimental efforts have shown that topological Kondo insulator is a promising building block for realizing spintronics and majorana fermions devices in future. Topological Kondo insulator extends the family of topological insulators by the intersection of topological insulator and heavy fermion (Kondo) compound. Topological insulator has attracted much interest in the field of condensed matter physics and material science recently because of its fundamentally novel physical phenomena, such as nontrivial gapless surface states protected by time reversal symmetry.
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