Quantum spin Hall （QSH） insulator is a new class of materials that is quickly becoming mainstream in condensed-matter physics. The main obstacle for the development of QSH insulators is that their strong interaction...Quantum spin Hall （QSH） insulator is a new class of materials that is quickly becoming mainstream in condensed-matter physics. The main obstacle for the development of QSH insulators is that their strong interactions with substrates make them difficult to study experimentally. In this study, using density functional theory, we discovered that MoTe2 is a good match for a GeI monolayer. The thermal stability of a van der Waals GeI/MoTe2 heterosheet was examined via molecular-dynamics simulations. Simulated scanning tunneling microscopy revealed that the GeI monolayer perfectly preserves the bulked honeycomb structure of MoTe2. The GeI on MoTe2 was confirmed to maintain its topological band structure with a sizable indirect bulk bandgap of 0.24 eV by directly calculating the spin Chern number to be -1. As expected, the electron mobility of the GeI is enhanced by MoTe2 substrate restriction. According to deformation- potential theory with the effective-mass approximation, the electron mobility of GeI/MoTe2 was estimated as 372.7 cm^2·s^-1·V^-1 at 300 K, which is 20 times higher than that of freestanding GeI. Our research shows that traditional substrates always destroy the topological states and hinder the electron transport in QSH insulators, and pave way for the further realization and utilization of QSH insulators at room temperature.展开更多
Nonsymmorphic symmetries open up horizons of exotic topological boundary states and even generalize the bulk–boundary correspondence,which,however,the third-order topological insulator in electronic materials are sti...Nonsymmorphic symmetries open up horizons of exotic topological boundary states and even generalize the bulk–boundary correspondence,which,however,the third-order topological insulator in electronic materials are still unknown.Here,by means of the symmetry analysis and k·p models,we uncover the emergence of long-awaited third-order topological insulators and the wallpaper fermions in space group I4/mcm(No.140).Based on this,we present the hourglass fermion,fourfold-degenerate Dirac fermion,and Möbius fermion in the(001)surface of Tl_(4)XTe_(3)(X=Pb/Sn)with a nonsymmorphic wallpaper group p4g.Remarkably,16 helical corner states reside on eight corners in Kramers pair,rendering the real electronic material of third-order topological insulators.More importantly,a time-reversal polarized octupole polarization is defined to uncover the nontrivial third-order topology,as is implemented by the 2nd and 3rd order Wilson loop calculations.Our results could considerably broaden the range of wallpaper fermions and lay the foundation for future experimental investigations of third-order topological insulators.展开更多
基金This work is supported by the National Basic Research Program of China （No. 2013CB632401）, National Natural Science Foundation of China （Nos. 21333006, 11374190, and 1140418）, and Program of Introducing Talents of Discipline to Universities （111 Program） （No. 297B13029）. We also thank the Taishan Scholar Program of Shandong Province.
文摘Quantum spin Hall （QSH） insulator is a new class of materials that is quickly becoming mainstream in condensed-matter physics. The main obstacle for the development of QSH insulators is that their strong interactions with substrates make them difficult to study experimentally. In this study, using density functional theory, we discovered that MoTe2 is a good match for a GeI monolayer. The thermal stability of a van der Waals GeI/MoTe2 heterosheet was examined via molecular-dynamics simulations. Simulated scanning tunneling microscopy revealed that the GeI monolayer perfectly preserves the bulked honeycomb structure of MoTe2. The GeI on MoTe2 was confirmed to maintain its topological band structure with a sizable indirect bulk bandgap of 0.24 eV by directly calculating the spin Chern number to be -1. As expected, the electron mobility of the GeI is enhanced by MoTe2 substrate restriction. According to deformation- potential theory with the effective-mass approximation, the electron mobility of GeI/MoTe2 was estimated as 372.7 cm^2·s^-1·V^-1 at 300 K, which is 20 times higher than that of freestanding GeI. Our research shows that traditional substrates always destroy the topological states and hinder the electron transport in QSH insulators, and pave way for the further realization and utilization of QSH insulators at room temperature.
基金This work was supported by the National Natural Science Foundation of China(Grants Nos.12174220,1904205 and 12074217)the Shandong Provincial Natural Science Foundation of China(Grants Nos.ZR2019QA019 and ZR2019MEM013)+1 种基金the Shandong Provincial Key Research and Development Program(Major Scientific and Technological Innovation Project)(Grant No.2019JZZY010302)the Qilu Young Scholar Program of Shandong University.
文摘Nonsymmorphic symmetries open up horizons of exotic topological boundary states and even generalize the bulk–boundary correspondence,which,however,the third-order topological insulator in electronic materials are still unknown.Here,by means of the symmetry analysis and k·p models,we uncover the emergence of long-awaited third-order topological insulators and the wallpaper fermions in space group I4/mcm(No.140).Based on this,we present the hourglass fermion,fourfold-degenerate Dirac fermion,and Möbius fermion in the(001)surface of Tl_(4)XTe_(3)(X=Pb/Sn)with a nonsymmorphic wallpaper group p4g.Remarkably,16 helical corner states reside on eight corners in Kramers pair,rendering the real electronic material of third-order topological insulators.More importantly,a time-reversal polarized octupole polarization is defined to uncover the nontrivial third-order topology,as is implemented by the 2nd and 3rd order Wilson loop calculations.Our results could considerably broaden the range of wallpaper fermions and lay the foundation for future experimental investigations of third-order topological insulators.
