An intrinsic magnetic topological insulator(TI) is a stoichiometric magnetic compound possessing both inherent magnetic order and topological electronic states. Such a material can provide a shortcut to various novel ...An intrinsic magnetic topological insulator(TI) is a stoichiometric magnetic compound possessing both inherent magnetic order and topological electronic states. Such a material can provide a shortcut to various novel topological quantum effects but remained elusive experimentally for a long time. Here we report the experimental realization of thin films of an intrinsic magnetic TI, MnBi2Te4, by alternate growth of a Bi2Te3 quintuple layer and a MnTe bilayer with molecular beam epitaxy. The material shows the archetypical Dirac surface states in angle-resolved photoemission spectroscopy and is demonstrated to be an antiferromagnetic topological insulator with ferromagnetic surfaces by magnetic and transport measurements as well as first-principles calculations. The unique magnetic and topological electronic structures and their interplays enable the material to embody rich quantum phases such as quantum anomalous Hall insulators and axion insulators at higher temperature and in a well-controlled way.展开更多
Recently,intrinsic antiferromagnetic topological insulator MnBi_(2)Te_(4) has drawn intense research interest and leads to plenty of significant progress in physics and materials science by hosting quantum anomalous H...Recently,intrinsic antiferromagnetic topological insulator MnBi_(2)Te_(4) has drawn intense research interest and leads to plenty of significant progress in physics and materials science by hosting quantum anomalous Hall effect,axion insulator state,and other quantum phases.An essential ingredient to realize these quantum states is the magnetic gap in the topological surface states induced by the out-of-plane ferromagnetism on the surface of MnBi_(2)Te_(4).However,the experimental observations of the surface gap remain controversial.Here,we report the observation of the surface gap via the point contact tunneling spectroscopy.In agreement with theoretical calculations,the gap size is around 50 me V,which vanishes as the sample becomes paramagnetic with increasing temperature.The magnetoresistance hysteresis is detected through the point contact junction on the sample surface with an out-of-plane magnetic field,substantiating the surface ferromagnetism.Furthermore,the non-zero transport spin polarization coming from the ferromagnetism is determined by the point contact Andreev reflection spectroscopy.Combining these results,the magnetism-induced gap in topological surface states of MnBi_(2)Te_(4) is revealed.展开更多
Layered material indium selenide(InxSey)is a promising candidate for building next-generation electronic and photonic devices.We report a zirconium aided MBE growth of this van der Waals material.When co-depositing zi...Layered material indium selenide(InxSey)is a promising candidate for building next-generation electronic and photonic devices.We report a zirconium aided MBE growth of this van der Waals material.When co-depositing zirconium and selenium onto an indium phosphide substrate with a substrate temperature of 400℃at a constant zirconium flux rate of 0.01 ML/min,the polymorphic Inx Sey layer emerges on top of the insulating ZrSe2 layer.Different archetypes,such as InSe,α-In2Se3 and α-In2Se3,are found in the InxSey layers.A negative magnetoresistance of 40%at 2 K under 9 T magnetic field is observed.Such an InxSeyZrSe2 heterostructure with good lattice-matching may serve as a candidate for device applications.展开更多
The recent discovery of topological insulators（TIs） offers new opportunities for the development of thermoelectrics,because many TIs（like Bi2Te3） are excellent thermoelectric（TE） materials.In this review,we will...The recent discovery of topological insulators（TIs） offers new opportunities for the development of thermoelectrics,because many TIs（like Bi2Te3） are excellent thermoelectric（TE） materials.In this review,we will first describe the general TE properties of TIs and show that the coexistence of the bulk and boundary states in TIs introduces unusual TE properties,including strong size effects and an anomalous Seebeck effect.Importantly,the TE figure of merit zT of TIs is no longer an intrinsic property,but depends strongly on the geometric size.The geometric parameters of twodimensional TIs can be tuned to enhance zT to be significantly greater than 1.Then a few proof-of-principle experiments on three-dimensional TIs will be discussed,which observed unconventional TE phenomena that are closely related to the topological nature of the materials.However,current experiments indicate that the metallic surface states,if their advantage of high mobility is not fully utilized,would be detrimental to TE performance.Finally,we provide an outlook for future work on topological materials,which offers great possibilities to discover exotic TE effects and may lead to significant breakthroughs in improving zT.展开更多
基金Supported by the Ministry of Science and Technology of Chinathe National Science Foundation of Chinathe Beijing Advanced Innovation Center for Future Chip(ICFC)
文摘An intrinsic magnetic topological insulator(TI) is a stoichiometric magnetic compound possessing both inherent magnetic order and topological electronic states. Such a material can provide a shortcut to various novel topological quantum effects but remained elusive experimentally for a long time. Here we report the experimental realization of thin films of an intrinsic magnetic TI, MnBi2Te4, by alternate growth of a Bi2Te3 quintuple layer and a MnTe bilayer with molecular beam epitaxy. The material shows the archetypical Dirac surface states in angle-resolved photoemission spectroscopy and is demonstrated to be an antiferromagnetic topological insulator with ferromagnetic surfaces by magnetic and transport measurements as well as first-principles calculations. The unique magnetic and topological electronic structures and their interplays enable the material to embody rich quantum phases such as quantum anomalous Hall insulators and axion insulators at higher temperature and in a well-controlled way.
基金Supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0303302,2018YFA0305604,2018YFA0307100)the National Natural Science Foundation of China (Grant Nos. 11888101,11774008,11704279,11874035,51788104)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000)the Beijing Natural Science Foundation (Grant Nos. Z180010 and 1202005)the Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics,Tsinghua University (Grant No. KF202001)
文摘Recently,intrinsic antiferromagnetic topological insulator MnBi_(2)Te_(4) has drawn intense research interest and leads to plenty of significant progress in physics and materials science by hosting quantum anomalous Hall effect,axion insulator state,and other quantum phases.An essential ingredient to realize these quantum states is the magnetic gap in the topological surface states induced by the out-of-plane ferromagnetism on the surface of MnBi_(2)Te_(4).However,the experimental observations of the surface gap remain controversial.Here,we report the observation of the surface gap via the point contact tunneling spectroscopy.In agreement with theoretical calculations,the gap size is around 50 me V,which vanishes as the sample becomes paramagnetic with increasing temperature.The magnetoresistance hysteresis is detected through the point contact junction on the sample surface with an out-of-plane magnetic field,substantiating the surface ferromagnetism.Furthermore,the non-zero transport spin polarization coming from the ferromagnetism is determined by the point contact Andreev reflection spectroscopy.Combining these results,the magnetism-induced gap in topological surface states of MnBi_(2)Te_(4) is revealed.
基金Supported by the National Natural Science Foundation of China(Grant No.11874233).
文摘Layered material indium selenide(InxSey)is a promising candidate for building next-generation electronic and photonic devices.We report a zirconium aided MBE growth of this van der Waals material.When co-depositing zirconium and selenium onto an indium phosphide substrate with a substrate temperature of 400℃at a constant zirconium flux rate of 0.01 ML/min,the polymorphic Inx Sey layer emerges on top of the insulating ZrSe2 layer.Different archetypes,such as InSe,α-In2Se3 and α-In2Se3,are found in the InxSey layers.A negative magnetoresistance of 40%at 2 K under 9 T magnetic field is observed.Such an InxSeyZrSe2 heterostructure with good lattice-matching may serve as a candidate for device applications.
基金Project supported by the National Thousand-Young-Talents Program,ChinaTsinghua University Initiative Scientific Research Program,China
文摘The recent discovery of topological insulators（TIs） offers new opportunities for the development of thermoelectrics,because many TIs（like Bi2Te3） are excellent thermoelectric（TE） materials.In this review,we will first describe the general TE properties of TIs and show that the coexistence of the bulk and boundary states in TIs introduces unusual TE properties,including strong size effects and an anomalous Seebeck effect.Importantly,the TE figure of merit zT of TIs is no longer an intrinsic property,but depends strongly on the geometric size.The geometric parameters of twodimensional TIs can be tuned to enhance zT to be significantly greater than 1.Then a few proof-of-principle experiments on three-dimensional TIs will be discussed,which observed unconventional TE phenomena that are closely related to the topological nature of the materials.However,current experiments indicate that the metallic surface states,if their advantage of high mobility is not fully utilized,would be detrimental to TE performance.Finally,we provide an outlook for future work on topological materials,which offers great possibilities to discover exotic TE effects and may lead to significant breakthroughs in improving zT.
