期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 112, 期 5, 页码 1316-1321出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1424322112
关键词
ferromagnetic topological insulator; Dirac-mass gapmap; Dirac-mass disorder; magnetic dopant atoms
资金
- US Department of Energy [DE-AC02-98CH10886]
- Institute of Basic Science of Korea [IBS-R009-D1]
- J. P. Reid under Engineering and Physical Sciences Research Council Programme Grant Topological Protection and Non-Equilibrium States in Correlated Electron Systems
- EPSRC [EP/I031014/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/I031014/1] Funding Source: researchfish
- Ministry of Science, ICT & Future Planning, Republic of Korea [IBS-R009-D1-2015-A00] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a Dirac-mass gap in their spectrum by breaking time-reversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr-0.08(Bi0.1Sb0.9)(1.92)Te-3. Simultaneous visualization of the Dirac-mass gap Delta(r) reveals its intense disorder, which we demonstrate is directly related to fluctuations in n(r), the Cr atom areal density in the termination layer. We find the relationship of surface-state Fermi wavevectors to the anisotropic structure of Delta(r) not inconsistent with predictions for surface ferromagnetism mediated by those states. Moreover, despite the intense Dirac-mass disorder, the anticipated relationship Delta(r) alpha n(r) is confirmed throughout and exhibits an electron-dopant interaction energy J* = 145 meV.nm(2). These observations reveal how magnetic dopant atoms actually generate the TI mass gap locally and that, to achieve the novel physics expected of time-reversal symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential.
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