Origin of the low critical observing temperature of the quantum anomalous Hall effect in V-doped (Bi, Sb)2Te3 film
W. LiMartin ClaassenCui‐Zu ChangBrian MoritzTao JiaC. ZhangSlavko RebecJ. J. LeeMakoto HashimotoDong-Hui LuR. G. MooreJagadeesh S. MooderaThomas DevereauxZhi‐Xun Shen
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Abstract The experimental realization of the quantum anomalous Hall (QAH) effect in magnetically-doped (Bi, Sb) 2 Te 3 films stands out as a landmark of modern condensed matter physics. However, ultra-low temperatures down to few tens of mK are needed to reach the quantization of Hall resistance, which is two orders of magnitude lower than the ferromagnetic phase transition temperature of the films. Here, we systematically study the band structure of V-doped (Bi, Sb) 2 Te 3 thin films by angle-resolved photoemission spectroscopy (ARPES) and show unambiguously that the bulk valence band (BVB) maximum lies higher in energy than the surface state Dirac point. Our results demonstrate clear evidence that localization of BVB carriers plays an active role and can account for the temperature discrepancy.Keywords:
Topological insulator
We introduce the anomalous Hall effect and its intrinsic mechanism,and then discuss the quantized anomalous Hall effect(QAHE).From the viewpoint of topological order,we focus on the differences and relationships among the quantum Hall effect,quantum spin Hall effect,QAHE,and topological insulators.Finally,we discuss the proposal that QAHE can be realized in thin films made of magnetic topological insulators such as Bi2Se3,Bi2Te3 and Sb2Te3 doped with Cr or Fe.
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Using high-resolution Nano-Angle Resolved Photoemission Spectroscopy (Nano-ARPES), we have determined the electronic structure of the surface and bulk states of topological insulator Sb2Te3 nanowires, which have been also characterized by magnetoresistance measurements. The observed Aharonov-Bohm-type oscillations could be unambiguously related to the transport by topological protected surface states directly recorded by photoemission. We have measured Nano-ARPES on individual nanowires of a few nanometers wide to provide direct evidence of the existence of the nontrivial topological surface states, as well as their doping. Our findings are consistent with theoretical predictions and confirm that the surface states of intrinsically doped unidimensional topological insulator nanowires are responsible for the quantum transport.
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Quantum anomalous Hall effect (QAHE) has been experimentally observed in magnetically doped topological insulators. However, ultralow temperatures (usually below 300 mK), which are mainly attributed to inhomogeneous magnetic doping, become a daunting challenge for potential applications. Here, a nonmagnetic-doping strategy is proposed to produce ferromagnetism and realize QAHE in topological insulators. We numerically demonstrate that magnetic moments can be induced by nonmagnetic nitrogen or carbon substitution in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3},$ ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3},$ and ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$, while only nitrogen-doped ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ system can exhibit long-range ferromagnetism and preserve large bulk band gaps. We further show that its corresponding thin film can harbor QAHE at temperatures of 17--29 Kelvin, which is two orders of magnitude higher than typical realized temperatures in similar systems. Our proposed nonmagnetic doping scheme may shed light on experimental realization of high-temperature QAHE in topological insulators.
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角度分解光電子分光法（ARPES）は，固体とその表面の電子構造の運動量依存性，すなわち電子構造のバンド分散 ε(k)を測定する有力な実験手法である．ARPESは低次元（一次元あるいは二次元）相関電子系における準粒子励起における電子相関の影響を調べるための理想的な手法でもある．本稿では，自由電子的な三次元系から低次元強相関電子系までの系に対するARPESの代表的な研究とその有効性について概説する．
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•van der Waals material MnBi2Te4 is an intrinsic antiferromagnetic topological insulator•Under moderate magnetic field, MnBi2Te4 may become a magnetic Weyl semimetal•MnBi2Te4 and its family of materials have brought great progress in studying novel topological quantum states•Quantum anomalous Hall effect above the liquid-nitrogen temperature can be expected in MnBi2Te4-related systems Introducing magnetism into topological insulators breaks time-reversal symmetry, and the magnetic exchange interaction can open a gap in the otherwise gapless topological surface states. This allows various novel topological quantum states to be generated, including the quantum anomalous Hall effect (QAHE) and axion insulator states. Magnetic doping and magnetic proximity are viewed as being useful means of exploring the interaction between topology and magnetism. However, the inhomogeneity of magnetic doping leads to complicated magnetic ordering and small exchange gaps, and consequently the observed QAHE appears only at ultralow temperatures. Therefore, intrinsic magnetic topological insulators are highly desired for increasing the QAHE working temperature and for investigating topological quantum phenomena further. The realization and characterization of such systems are essential for both fundamental physics and potential technical revolutions. This review summarizes recent research progress in intrinsic magnetic topological insulators, focusing mainly on the antiferromagnetic topological insulator MnBi2Te4 and its family of materials. Introducing magnetism into topological insulators breaks time-reversal symmetry, and the magnetic exchange interaction can open a gap in the otherwise gapless topological surface states. This allows various novel topological quantum states to be generated, including the quantum anomalous Hall effect (QAHE) and axion insulator states. Magnetic doping and magnetic proximity are viewed as being useful means of exploring the interaction between topology and magnetism. However, the inhomogeneity of magnetic doping leads to complicated magnetic ordering and small exchange gaps, and consequently the observed QAHE appears only at ultralow temperatures. Therefore, intrinsic magnetic topological insulators are highly desired for increasing the QAHE working temperature and for investigating topological quantum phenomena further. The realization and characterization of such systems are essential for both fundamental physics and potential technical revolutions. This review summarizes recent research progress in intrinsic magnetic topological insulators, focusing mainly on the antiferromagnetic topological insulator MnBi2Te4 and its family of materials.
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