Magnetic topological quantum materials(TQMs) provide a fertile ground for the emergence of fascinating topological magneto-electric effects. Recently, the discovery of intrinsic antiferromagnetic(AFM) topological insu...Magnetic topological quantum materials(TQMs) provide a fertile ground for the emergence of fascinating topological magneto-electric effects. Recently, the discovery of intrinsic antiferromagnetic(AFM) topological insulator MnBi_(2)Te_(4) that could realize quantized anomalous Hall effect and axion insulator phase ignited intensive study on this family of TQM compounds. Here, we investigated the AFM compound Mn Bi4 Te7 where Bi_(2)Te_(3) and MnBi_(2)Te_(4) layers alternate to form a superlattice. Using spatial-and angleresolved photoemission spectroscopy, we identified ubiquitous(albeit termination dependent) topological electronic structures from both Bi_(2)Te_(3) and MnBi_(2)Te_(4) terminations. Unexpectedly, while the bulk bands show strong temperature dependence correlated with the AFM transition, the topological surface states with a diminishing gap show negligible temperature dependence across the AFM transition.Together with the results of its sister compound MnBi_(2)Te_(4), we illustrate important aspects of electronic structures and the effect of magnetic ordering in this family of magnetic TQMs.展开更多
Thermoelectric materials(TMs)can uniquely convert waste heat into electricity,which provides a potential solution for the global energy crisis that is increasingly severe.Bulk Cu2Se,with ionic conductivity of Cu ions,...Thermoelectric materials(TMs)can uniquely convert waste heat into electricity,which provides a potential solution for the global energy crisis that is increasingly severe.Bulk Cu2Se,with ionic conductivity of Cu ions,exhibits a significant enhancement of its thermoelectric figure of merit z T by a factor of^3 near its structural transition around 400 K.Here,we show a systematic study of the electronic structure of Cu2Se and its temperature evolution using high-resolution angle-resolved photoemission spectroscopy.Upon heating across the structural transition,the electronic states near the corner of the Brillouin zone gradually disappear,while the bands near the centre of Brillouin zone shift abruptly towards high binding energies and develop an energy gap.Interestingly,the observed band reconstruction well reproduces the temperature evolution of the Seebeck coefficient of Cu2 Se,providing an electronic origin for the drastic enhancement of the thermoelectric performance near 400 K.The current results not only bridge among structural phase transition,electronic structures and thermoelectric properties in a condensed matter system,but also provide valuable insights into the search and design of new generation of thermoelectric materials.展开更多
基金supported by the National Key Research and Development Program of China (2017YFA0305400, 2017YFA0304600, 2018YFA0307100, and 2018YFA0305603)the National Natural Science Foundation of China (11774190, 11674229, 11634009, 11774427, 51788104, and 11874035)+1 种基金EPSRC Platform Grant (EP/M020517/1)the support from the Shanghai Pujiang Program (17PJ1406200)。
文摘Magnetic topological quantum materials(TQMs) provide a fertile ground for the emergence of fascinating topological magneto-electric effects. Recently, the discovery of intrinsic antiferromagnetic(AFM) topological insulator MnBi_(2)Te_(4) that could realize quantized anomalous Hall effect and axion insulator phase ignited intensive study on this family of TQM compounds. Here, we investigated the AFM compound Mn Bi4 Te7 where Bi_(2)Te_(3) and MnBi_(2)Te_(4) layers alternate to form a superlattice. Using spatial-and angleresolved photoemission spectroscopy, we identified ubiquitous(albeit termination dependent) topological electronic structures from both Bi_(2)Te_(3) and MnBi_(2)Te_(4) terminations. Unexpectedly, while the bulk bands show strong temperature dependence correlated with the AFM transition, the topological surface states with a diminishing gap show negligible temperature dependence across the AFM transition.Together with the results of its sister compound MnBi_(2)Te_(4), we illustrate important aspects of electronic structures and the effect of magnetic ordering in this family of magnetic TQMs.
基金the National Natural Science Foundation of China(11774190,11674229,11634009 and 11874264)the National Key R&D Program of China(2017YFA0304600,2017YFA0305400 and 2017YFA0402900)+2 种基金EPSRC Platform Grant(EP/M020517/1)the support from the Natural Science Foundation of Shanghai(17ZR1443300)the support from Tsinghua University Initiative Scientific Research Program。
文摘Thermoelectric materials(TMs)can uniquely convert waste heat into electricity,which provides a potential solution for the global energy crisis that is increasingly severe.Bulk Cu2Se,with ionic conductivity of Cu ions,exhibits a significant enhancement of its thermoelectric figure of merit z T by a factor of^3 near its structural transition around 400 K.Here,we show a systematic study of the electronic structure of Cu2Se and its temperature evolution using high-resolution angle-resolved photoemission spectroscopy.Upon heating across the structural transition,the electronic states near the corner of the Brillouin zone gradually disappear,while the bands near the centre of Brillouin zone shift abruptly towards high binding energies and develop an energy gap.Interestingly,the observed band reconstruction well reproduces the temperature evolution of the Seebeck coefficient of Cu2 Se,providing an electronic origin for the drastic enhancement of the thermoelectric performance near 400 K.The current results not only bridge among structural phase transition,electronic structures and thermoelectric properties in a condensed matter system,but also provide valuable insights into the search and design of new generation of thermoelectric materials.
