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Nanophotonic Devices Based on Low-Voltage Emission of 2D Electron Gas
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Hong Koo Kim, Myungji Kim, Daud Emon, Siyang Liu, Yu Shi, Haiming Guo
The 2DES phenomenon has been observed in a variety of heterogeneous materials interfaces, broadly termed heterostructures. The best known examples are carriers confined to the vicinity of junctions between insulators and semiconductors, such as metal-oxide-semiconductor (MOS) structure, between layers of different semiconductors, such as heterojunctions of III-V, II-VI or III-VI compounds, and intercalated graphite. Electrons can also be confined to the surface of a material. Free electrons, for example, can float and move along on the surface of liquid helium: some of the earlier work in 2DEG utilized the carrier confinement effect of an image-charge potential formed on helium surface (Sommer 1964). More recently, it has been found that solid insulators, such as topological insulators, can also support conductive surface electronic states [topological insulators].
Introducing Topological Materials: Mind the Time Reversal
Published in Grigory Tkachov, Topological Quantum Materials, 2015
This chapter acquaints the reader with the notion of topological insulators and related quantum materials. Topological insulators are two- or three-dimensional materials with an insulating interior and a conducting edge or surface supporting mobile carriers. As we shall see, the emergence of topological insulators is a vivid example of the importance of fundamental symmetries in physics. In this case, it is the symmetry with respect to the reversal of the arrow of time. We, therefore, begin with a discussion of general ideas about time-reversal invariance and its violation, which will lead us step by step to the notion of topological insulators. Their conducting states possess robust quantum properties such as helicity and chirality. These will be the central concepts in our discussion of the two-dimensional topological insulators—quantum spin Hall and anomalous Hall insulators—and their three-dimensional analogues. Similar types of conducting states are encountered in other quantum materials, notably in Weyl semimetals and topological superconductors. These will be introduced in this chapter on an equal footing with topological insulators. The general goal is to focus on basic ideas and concepts rather than on theoretical details and comprehensive literature review.
Related 2D-Material Detectors
Published in Antoni Rogalski, 2D Materials for Infrared and Terahertz Detectors, 2020
Recently, it was demonstrated that topological insulators can also be promising candidate materials for broadband photodetection, including the THz range. Topological insulators (TIs) represent a novel quantum phase of matter, characterized by a semiconducting bulk and topologically protected surface states, with spin and momentum helical locking and a Dirac-like band structure [33,34]. 2D TIs are associated with gapless edge states, and three-dimensional (3D) insulators with gapless topological surface states (TSS) [35].
Temporal and amplitude modulation at C-band region using Bi2Te3-based optical modulator
Published in Journal of Modern Optics, 2020
Harith Ahmad, Norazriena Yusoff, Hwee San Lim, Mohd. Zubir Mat Jafri, Mohd. Zamani Zulkifli, Zian Cheak Tiu
Since the discovery of graphene and its unique optoelectronic properties, significant research efforts have been made towards finding other materials with similarly unique properties. Of the many materials studies, topological insulators (TIs) have garnered significant interest due to its unique charge and spin properties [1]. With strong spin–orbit coupling and time reversal symmetry, TIs exhibit gapless metallic states on its surface [2,3]. Additionally, the existence of quantum spin Hall effects without the involvement of external magnetic fields has been verified in two-dimensional (2D) TI materials [4,5]. These extraordinary electronic properties make TIs highly potential materials for the development of next-generation optoelectronics technologies [6] and also as saturable absorbers (SAs) to obtain optical modulation in laser cavities [7–9].
First-principles investigations on elastic, thermodynamic and lattice thermal conductivity of topological insulator LaAs
Published in Philosophical Magazine, 2018
Yu Zhou, Yan Cheng, Xiang-Rong Chen, Cui-E Hu, Qi-Feng Chen
Non-trivial topological quantum materials (TQMs), such as topological insulators (TIs) [1–6], Dirac semimetals (DSMs) [7–11] and Weyl semimetals (WSMs) [12–14], have become one of the most popular and important research fields in condensed matter physics and materials. It is noted that TIs are always a hotspot because of their especial intrinsic properties with a bulk band gap and unusual conducting states on their edge or surface [15,16]. Topological insulator was first theoretically predicted [1] and experimentally observed [17] in HgTe quantum wells. Later, a class of three-dimensional topological insulators were identified with the surface state consisting of a single Dirac cone [18–20]. Many of these materials have unique physical properties such as large unsaturated magneto resistance, quantum anomalous Hall effect and novel quantum oscillations [21–23]. These distinguishing features determine many significant technological applications of topological insulators, such as spintronics and quantum information processing.
Recent advances in two-dimensional ferromagnetism: strain-, doping-, structural- and electric field-engineering toward spintronic applications
Published in Science and Technology of Advanced Materials, 2022
Sheng Yu, Junyu Tang, Yu Wang, Feixiang Xu, Xiaoguang Li, Xinzhong Wang
Firstly, it is always urgently needed and promising for discovering new members of 2D magnetic materials with high-transition temperatures, high coercive field and good environmental stability. Most currently available 2D magnets possess low phase transition temperature far below room temperature [7]. Meanwhile, the stability is another great challenge that most 2D materials with atomic thickness are susceptible to temperature effect, oxygenation, moisture and other chemical corrosion [20]. Also, the exploration of low-dimensional magnetic topological insulators with topological spin textures and intrinsic chiral helimagnetism is crucial for developing their practical applications in dissipationless topological electronics and topological quantum computation.