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
We report high-resolution scanning tunneling microscopy(STM)study of nano-sized Pb islands grown on SrTiO3,where three distinct types of gaps with different energy scales are revealed.At low temperature,we find that t...We report high-resolution scanning tunneling microscopy(STM)study of nano-sized Pb islands grown on SrTiO3,where three distinct types of gaps with different energy scales are revealed.At low temperature,we find that the superconducting gap(△s)in nano-sized Pb islands is significantly enhanced from the one in bulk Pb,while there is no essential change in superconducting transition temperature Tc,giving rise to a larger BCS ratio 2△s/kBTc^8.31 and implying stronger electron-phonon coupling.The stronger coupling can originate from the interface electron-phonon interactions between Pb islands and SrTiO3.As the superconducting gap is totally suppressed under applied magnetic field,the Coulomb gap with apparent V-shape emerges.Moreover,the size of Coulomb gap(Ac)depends on the lateral size of Pb islands(R)with △c-1/R^035,indicating that quantum size effect can significantly influence electronic correlations.Our experimental results shall shed important light on the interplay among superconductivity,quantum size effect and correlations in nano-sized strong-coupling superconductors.展开更多
Pb nanobridges with a thickness of less than 10 nm and a width of several hundred nm have been fabricated from single-crystalline Pb fi lms using low-temperature molecular beam epitaxy and focus ion beam microfabricat...Pb nanobridges with a thickness of less than 10 nm and a width of several hundred nm have been fabricated from single-crystalline Pb fi lms using low-temperature molecular beam epitaxy and focus ion beam microfabrication techniques.We observed novel magnetoresistance oscillations below the superconducting transition temperature(TC)of the bridges.The oscillations which were not seen in the crystalline Pb fi lmsmay originate from the inhomogeneity of superconductivity induced by the applied magnetic fi elds on approaching the normal state,or the degradation of fi lm quality by thermal evolution.展开更多
The chirality associated with broken time-reversal symmetry in magnetically doped topological insulators has important implications for the quantum transport phenomena.Here we report anomalous Hall effect studies in M...The chirality associated with broken time-reversal symmetry in magnetically doped topological insulators has important implications for the quantum transport phenomena.Here we report anomalous Hall effect studies in Mn-and Cr-doped Bi_(2)Te_(3) topological insulators with varied thicknesses and doping contents.By tracing the magnitude of the anomalous Hall resistivity,we find that the Mn-type anomalous Hall effect characterized with clockwise chirality is strengthened by the reduction of film thickness,which is opposite to that of the Cr-type anomalous Hall effect with counterclockwise chirality.We provide a phenomenological physical picture to explain the evolution of the magnetic order and the anomalous Hall chirality in magnetically doped topological insulators.展开更多
The growth and characterization of single-crystalline thin films of topological insulators(TIs)is an important step towards their possible applications.Using in situ scanning tunneling microscopy(STM)and angle-resolve...The growth and characterization of single-crystalline thin films of topological insulators(TIs)is an important step towards their possible applications.Using in situ scanning tunneling microscopy(STM)and angle-resolved photoemission spectroscopy(ARPES),we show that moderately thick Sb_(2)Te_(3)films grown layer-by-layer by molecular beam epitaxy(MBE)on Si(111)are atomically smooth,single-crystalline,and intrinsically insulating.Furthermore,these films were found to exhibit a robust TI electronic structure with their Fermi energy lying within the energy gap of the bulk that intersects only the Dirac cone of the surface states.Depositing Cs in situ moves the Fermi energy of the Sb_(2)Te_(3)films without changing the electronic band structure,as predicted by theory.We found that the TI behavior is preserved in Sb_(2)Te_(3)films down to five quintuple layers(QLs).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the National Natural Science Foundation under Grant Nos.11674191 and 11825404the National Key Program for S&T Research and Development under Grant No No.2016YFA0301002the Beijing Advanced Innovation Center for Future Chip(ICFC).W.L.was also supported by Beijing Young Talents Plan.
文摘We report high-resolution scanning tunneling microscopy(STM)study of nano-sized Pb islands grown on SrTiO3,where three distinct types of gaps with different energy scales are revealed.At low temperature,we find that the superconducting gap(△s)in nano-sized Pb islands is significantly enhanced from the one in bulk Pb,while there is no essential change in superconducting transition temperature Tc,giving rise to a larger BCS ratio 2△s/kBTc^8.31 and implying stronger electron-phonon coupling.The stronger coupling can originate from the interface electron-phonon interactions between Pb islands and SrTiO3.As the superconducting gap is totally suppressed under applied magnetic field,the Coulomb gap with apparent V-shape emerges.Moreover,the size of Coulomb gap(Ac)depends on the lateral size of Pb islands(R)with △c-1/R^035,indicating that quantum size effect can significantly influence electronic correlations.Our experimental results shall shed important light on the interplay among superconductivity,quantum size effect and correlations in nano-sized strong-coupling superconductors.
基金by the National Science Foundation and the Ministry of Science and Technology of China and the Penn.State MRSEC under NSF grant DMR-0820404.
文摘Pb nanobridges with a thickness of less than 10 nm and a width of several hundred nm have been fabricated from single-crystalline Pb fi lms using low-temperature molecular beam epitaxy and focus ion beam microfabrication techniques.We observed novel magnetoresistance oscillations below the superconducting transition temperature(TC)of the bridges.The oscillations which were not seen in the crystalline Pb fi lmsmay originate from the inhomogeneity of superconductivity induced by the applied magnetic fi elds on approaching the normal state,or the degradation of fi lm quality by thermal evolution.
基金This work was supported by the Basic Science Center Project of National Natural Science Foundation of China(Grant No.51788104)the National Key R&D Program of China(Grant Nos.2018YFA0307100,and 2018YFA0305603)This work was supported in part by the Beijing Advanced Innovation Center for Future Chip(ICFC).
文摘The chirality associated with broken time-reversal symmetry in magnetically doped topological insulators has important implications for the quantum transport phenomena.Here we report anomalous Hall effect studies in Mn-and Cr-doped Bi_(2)Te_(3) topological insulators with varied thicknesses and doping contents.By tracing the magnitude of the anomalous Hall resistivity,we find that the Mn-type anomalous Hall effect characterized with clockwise chirality is strengthened by the reduction of film thickness,which is opposite to that of the Cr-type anomalous Hall effect with counterclockwise chirality.We provide a phenomenological physical picture to explain the evolution of the magnetic order and the anomalous Hall chirality in magnetically doped topological insulators.
基金The work is supported by the National Natural Science Foundation of China(NSFC)the National Basic Research Program of the Ministry of Science and Technology of China(MOST)Work at Pennsylvania State University is supported by the National Science Foundation(NSF)under Grant No.DMR 0908700.
文摘The growth and characterization of single-crystalline thin films of topological insulators(TIs)is an important step towards their possible applications.Using in situ scanning tunneling microscopy(STM)and angle-resolved photoemission spectroscopy(ARPES),we show that moderately thick Sb_(2)Te_(3)films grown layer-by-layer by molecular beam epitaxy(MBE)on Si(111)are atomically smooth,single-crystalline,and intrinsically insulating.Furthermore,these films were found to exhibit a robust TI electronic structure with their Fermi energy lying within the energy gap of the bulk that intersects only the Dirac cone of the surface states.Depositing Cs in situ moves the Fermi energy of the Sb_(2)Te_(3)films without changing the electronic band structure,as predicted by theory.We found that the TI behavior is preserved in Sb_(2)Te_(3)films down to five quintuple layers(QLs).
