Abstract
Quantum spin Hall (QSH) effect, a fundamentally new quantum state of matter and topological phase transitions are characteristics of a kind of electronic material, popularly referred to as topological insulators (TIs). TIs are similar to ordinary insulator in terms of their bulk bandgap, but have gapless conducting edge-states that are topologically protected. These edge-states are facilitated by the time-reversal symmetry and they are robust against nonmagnetic impurity scattering. Recently, the quest for new materials exhibiting non-trivial topological state of matter has been of great research interest, as TIs find applications in new electronics and spintronics and quantum-computing devices. Here, we propose and demonstrate as a proof-of-concept that QSH effect and topological phase transitions can be realized in /InSb semiconductor quantum wells (QWs). The simultaneous incorporation of nitrogen and bismuth in InSb is instrumental in lowering the bandgap, while inducing opposite kinds of strain to attain a near-lattice-matching conducive for lattice growth. Phase diagram for bandgap shows that as we increase the QW thickness, at a critical thickness, the electronic bandstructure switches from a normal to an inverted type. We confirm that such transition are topological phase transitions between a traditional insulator and a TI exhibiting QSH effect—by demonstrating the topologically protected edge-states using the bandstructure, edge-localized distribution of the wavefunctions and edge-state spin-momentum locking phenomenon, presence of non-zero conductance in spite of the Fermi energy lying in the bandgap window, crossover points of Landau levels in the zero-mode indicating topological band inversion in the absence of any magnetic field and presence of large Rashba spin-splitting, which is essential for spin-manipulation in TIs.
Highlights
25 July 2017912, Beijing 100083, Peoples Republic of China 3 Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, Peoples Republic of China 4 OPTIMUS, Centre for OptoElectronics and Biophotonics, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore 5 LUMINOUS!
Topological insulators (TIs) are a recently discovered class of electronic material that have a bulk bandgap similar to that of an ordinary insulator, but have gapless conducting states on their surface or edge that are topologically protected [1]
Based on the aforementioned premise, in this work we propose and verify as a proof-of-concept that InNxBiySb1-x-y/InSb quantum wells (QWs) grown along the [001] direction as a semiconductor system can effectively realize Quantum spin Hall (QSH) effect and topological phase transition
Summary
912, Beijing 100083, Peoples Republic of China 3 Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, Peoples Republic of China 4 OPTIMUS, Centre for OptoElectronics and Biophotonics, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore 5 LUMINOUS! 912, Beijing 100083, Peoples Republic of China 3 Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, Peoples Republic of China 4 OPTIMUS, Centre for OptoElectronics and Biophotonics, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore 5 LUMINOUS! Centre of Excellence for Semiconductor Lighting & Displays, Nanyang Technological University, Singapore 639798, Singapore 6 Author to whom any correspondence should be addressed
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