Introducing ferromagnetism into non-magnetic systems without the participation of magnetic elements is promising for all-electric spintronic devices[1,2].Many approaches have been pursued,such as non-magnetic defects ...Introducing ferromagnetism into non-magnetic systems without the participation of magnetic elements is promising for all-electric spintronic devices[1,2].Many approaches have been pursued,such as non-magnetic defects induced magnetization in layered materials[3–5]or the inversion symmetry breaking induced magnetization in magic-angle bilayer graphene[6–8],etc.However,these approaches have to tackle with the localization effects or the inevitable precise control of twist angle,which hinders the future application into large-scale spintronic information devices.Theorists also predicted that the spontaneous ferromagnetism could emerge in the quasi-2D crystals[9]like GaSe,but no experimental results have been reported.Here,we report the spontaneous ferromagnetism induced by van Hove singularity[9–13]in non-magnetic groupⅣGe_(1–x)Sn_(x)alloys grown by the molecular beam epitaxy(MBE)technique.Our findings experimentally open up an opportunity to realize spintronics in groupⅣsemiconductors.展开更多
We study the underlying symmetry in a spin-orbit coupled tight-binding model with Hubbard interaction.It is shown that,in the absence of the on-site interaction,the system possesses the SU(2)symmetry arising from the ...We study the underlying symmetry in a spin-orbit coupled tight-binding model with Hubbard interaction.It is shown that,in the absence of the on-site interaction,the system possesses the SU(2)symmetry arising from the time reversal symmetry.The influence of the on-site interaction on the symmetry depends on the topology of the networks:The SU(2)symmetry is shown to be the spin rotation symmetry of a simply-connected lattice even in the presence of the Hubbard interaction.On the contrary,the on-site interaction breaks the SU(2)symmetry of a multi-connected lattice.This fact indicates that a discrete spin-orbit coupled system has exclusive features from its counterpart in a continuous system.The obtained rigorous result is illustrated by a simple ring system.展开更多
In this article we review recent transport property studies on topological insulator thin films grown by molecular beam epitaxy.In pure Bi2Se3 ultrathin films we find an insulating ground state in the presence of weak...In this article we review recent transport property studies on topological insulator thin films grown by molecular beam epitaxy.In pure Bi2Se3 ultrathin films we find an insulating ground state in the presence of weak antilocalization,which indicates the relevance of electron interaction effect.In magnetically doped Bi2Se3 film we observe a systematic crossover between weak localization and weak antilocalization with varied magnetic doping,temperature,and magnetic field.These results demonstrate the intricate interplay between topological delocalization,electron interaction,and broken time reversal symmetry in topological insulator thin films.展开更多
基金the Key-Area Research and Development Program of Guangdong Province(2020B0303060001,and 2018B030327001)the National Natural Science Foundation of China(61874109,61922077,12004158,and 12074162)+1 种基金the National Key Research and Development Program of China(2018YFB2200100,and 2020YFA0309300)Guangdong Provincial Key Laboratory(2019B121203002)。
文摘Introducing ferromagnetism into non-magnetic systems without the participation of magnetic elements is promising for all-electric spintronic devices[1,2].Many approaches have been pursued,such as non-magnetic defects induced magnetization in layered materials[3–5]or the inversion symmetry breaking induced magnetization in magic-angle bilayer graphene[6–8],etc.However,these approaches have to tackle with the localization effects or the inevitable precise control of twist angle,which hinders the future application into large-scale spintronic information devices.Theorists also predicted that the spontaneous ferromagnetism could emerge in the quasi-2D crystals[9]like GaSe,but no experimental results have been reported.Here,we report the spontaneous ferromagnetism induced by van Hove singularity[9–13]in non-magnetic groupⅣGe_(1–x)Sn_(x)alloys grown by the molecular beam epitaxy(MBE)technique.Our findings experimentally open up an opportunity to realize spintronics in groupⅣsemiconductors.
基金supported by the National Natural Science Foundation of China(Grant No.11374163)the National Basic Research Program of China(Grant No.2012CB921900)
文摘We study the underlying symmetry in a spin-orbit coupled tight-binding model with Hubbard interaction.It is shown that,in the absence of the on-site interaction,the system possesses the SU(2)symmetry arising from the time reversal symmetry.The influence of the on-site interaction on the symmetry depends on the topology of the networks:The SU(2)symmetry is shown to be the spin rotation symmetry of a simply-connected lattice even in the presence of the Hubbard interaction.On the contrary,the on-site interaction breaks the SU(2)symmetry of a multi-connected lattice.This fact indicates that a discrete spin-orbit coupled system has exclusive features from its counterpart in a continuous system.The obtained rigorous result is illustrated by a simple ring system.
基金supported by the National Natural Science Foundation of China(Grant Nos.10834003,10911130233)the Ministry of Science and Technology of China(Grant No.2009CB929400)the Chinese Academy of Sciences
文摘In this article we review recent transport property studies on topological insulator thin films grown by molecular beam epitaxy.In pure Bi2Se3 ultrathin films we find an insulating ground state in the presence of weak antilocalization,which indicates the relevance of electron interaction effect.In magnetically doped Bi2Se3 film we observe a systematic crossover between weak localization and weak antilocalization with varied magnetic doping,temperature,and magnetic field.These results demonstrate the intricate interplay between topological delocalization,electron interaction,and broken time reversal symmetry in topological insulator thin films.
