Two‐Dimensional Van Der Waals Topological Materials: Preparation, Properties, and Device Applications

Abstract

Over the past decade, 2D van der Waals (vdW) topological materials (TMs), including topological insulators and topological semimetals, which combine atomically flat 2D layers and topologically nontrivial band structures, have attracted increasing attention in condensed‐matter physics and materials science. These easily cleavable and integrated TMs provide the ideal platform for exploring topological physics in the 2D limit, where new physical phenomena may emerge, and represent a potential to control and investigate exotic properties and device applications in nanoscale topological phases. However, multifaced efforts are still necessary, which is the prerequisite for the practical application of 2D vdW TMs. Herein, this review focuses on the preparation, properties, and device applications of 2D vdW TMs. First, three common preparation strategies for 2D vdW TMs are summarized, including single crystal exfoliation, chemical vapor deposition, and molecular beam epitaxy. Second, the origin and regulation of various properties of 2D vdW TMs are introduced, involving electronic properties, transport properties, optoelectronic properties, thermoelectricity, ferroelectricity, and magnetism. Third, some device applications of 2D vdW TMs are presented, including field‐effect transistors, memories, spintronic devices, and photodetectors. Finally, some significant challenges and opportunities for the practical application of 2D vdW TMs in 2D topological electronics are briefly addressed.

Crystal Growth and Room-Temperature Intrinsic Anomalous Hall Effect in Cr0.03Sn0.05Pb0.02Te0.1 Ferromagnetic Crystals

“…Since SnTe is a well-known TCI, 1,34−36 some Cr-doped SnTe are also considered as TCI verifying the characteristics of TCI materials. 2,37 So, we also check electronic characteristics in Cr 0.03 Pb 0.02 Sn 0.05 Te 0.1 crystal sheets. In TCI, the topological surface effect causes the conductivity to rise dramatically as the thickness decreases, especially for greater surface ratios and larger topological s u r f a c e e ff e c t s .…”

“…The conductivity of two different thicknesses of magnetic crystal sheets was measured with a four-terminal Hall device using PPMS and showing the typical metallic nature (conductivity of crystal sheets decreases with the rise of temperature) that can be clearly seen in Figure a,b, while the insets of these plots show the optical images of Hall devices. Since SnTe is a well-known TCI, ,− some Cr-doped SnTe are also considered as TCI verifying the characteristics of TCI materials. , So, we also check electronic characteristics in Cr 0.03 Pb 0.02 Sn 0.05 Te 0.1 crystal sheets. In TCI, the topological surface effect causes the conductivity to rise dramatically as the thickness decreases, especially for greater surface ratios and larger topological surface effects.…”

“…3 Magnetic topological crystalline insulators are used in next-generation electronic devices, including those for low-power spintronic, dissipationless topological electronics, and topological quantum computation. 2,4 Magnetism breaks time reversal symmetry in topological insulators, and the magnetic exchange interaction can introduce a gap into the gapless topological surface states. To implement the QAHE in TIs, magnetic proximity 5 and magnetic doping 6 are viewed as promising methods for introducing magnetism.…”

“…One of the novel forms of topological insulators (TIs) is a topological crystalline insulator (TCI), in which the topological character of electronic structures is protected by the crystal’s symmetries. , However, the combined effect of both the topological crystalline insulating phase and an intrinsic ferromagnetic order is expected to realize a quantum anomalous Hall effect (QAHE) with unusual features due to the interplay between the topology of their electronic wave functions and the magnetic spin configuration . Magnetic topological crystalline insulators are used in next-generation electronic devices, including those for low-power spintronic, dissipationless topological electronics, and topological quantum computation. , …”

Fourier‐Transform Infrared Spectroscopy of MoTe2 Thin Films

“…They are at the center of attention due to their distinctive properties in photonics and optoelectronics. [ 1,2 ] Some TMDs exhibit indirect‐to‐direct bandgap transition when thinned down to monolayer. The result is strong photoluminescence that coexists with large exciton binding energies and strong spin‐valley coupling, making TMDs attractive for new optoelectronic devices.…”