Low-Dimensional Topological Crystalline Insulators

Abstract

Topological crystalline insulators (TCIs) are recently discovered topological phase with robust surface states residing on high-symmetry crystal surfaces. Different from conventional topological insulators (TIs), protection of surface states on TCIs comes from point-group symmetry instead of time-reversal symmetry in TIs. The distinct properties of TCIs make them promising candidates for the use in novel spintronics, low-dissipation quantum computation, tunable pressure sensor, mid-infrared detector, and thermoelectric conversion. However, similar to the situation in TIs, the surface states are always suppressed by bulk carriers, impeding the exploitation of topology-induced quantum phenomenon. One effective way to solve this problem is to grow low-dimensional TCIs which possess large surface-to-volume ratio, and thus profoundly increase the carrier contribution from topological surface states. Indeed, through persistent effort, researchers have obtained unique quantum transport phenomenon, originating from topological surface states, based on controllable growth of low-dimensional TCIs. This article gives a comprehensive review on the recent progress of controllable synthesis and topological surface transport of low-dimensional TCIs. The possible future direction about low-dimensional TCIs is also briefly discussed at the end of this paper.

Unexpected Au Alloying in Tailoring In-Doped SnTe Nanostructures with Gold Nanoparticles

“…Soon after the discovery of SnTe a bulk TCI, several methods to grow SnTe nanostructures by vapor transport with Ar gas flow with/without a gold catalyst were reported [31][32][33][34][35][36]. These suggested that In-SnTe nanostructures can be made available with similar growth methods.…”

Two‐Dimensional Non‐Layered Materials: Synthesis, Properties and Applications

“…The prediction was then immediately confirmed by other three groups through angle‐resolved photoemission‐spectroscopy (APRES) in 2012 . Compared with TIs, TCIs exhibit three intriguing features: (1) they are of highly symmetry crystal structures, (2) gapless metallic states only reside on those mirror‐symmetry surfaces such as (100), (111), and (110), (3) Dirac cones on TCIs surface can be opened up by breaking symmetry, manipulating temperature, and tailoring compositions . For example, as shown in Figure b and c, there will be a non‐trivial to trivial topological phase transition while continuously varying the composition of Pb 1‐ x Sn x Te or changing the temperature tested.…”

“…Up to now, a variety of non‐layered materials have been synthesized successfully into 2D structures, including metals, metal oxides, metal chalcogenides, topological crystalline insulators, organic‐inorganic hybrid perovskites, and others. With this special 2D geometry, they have been studied as photodetectors, low‐dissipation logic devises, catalysts for water splitting and CO oxidation, and electrodes for Li‐ion batteries etc.…”

“…After that, the 2D structures will form through the following two ways: the nuclei grow up directly along the lateral directions (up process in Figure a); or the preformed small nanocrystals meet each other and coalesce for the demand of the lowest system energy (bottom process in Figure a). No matter which process it follows, two conditions need to be met: 1) 2D anisotropic growth is preferred through controlling the growth parameters, such as temperatures, pressures and gas flow rates; 2) adatoms/small nanocrystals are able to migrate/twist on the substrate surfaces . These requirements can be met by using dangling bond free substrates, like mica and 2D layered materials.…”

“…And the so‐called van der Waals epitaxial (vdWE) growth has exhibited great ability to realize highly anisotropic growth for 2D non‐layered materials. Different from the conventional epitaxial growth, such as metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), vdWE does not require strict requirement of lattice matching between the growing layer and the substrates because: (1) the vdWE substrates can act as the thermal mismatch buffer layer to relax the thermal stress, (2) the migration of the reaction precursors on the substrates can be further facilitated as a result of the relatively weak van der Waals interaction at the interfaces during epitaxial growth, thus resulting in highly anisotropic growth with relatively large lateral sizes, high crystal quality, and even defect‐free crystals …”