Duming Zhang, Anthony Richardella, Su-Yang Xu, David W. Rench, Abhinav Kandala, Thomas C. Flanagan, Haim Beidenkopf, Andrew L. Yeats, Bob B. Buckley, Paul V. Klimov, David D. Awschalom, Ali Yazdani, Peter Schiffer, M. Zahid Hasan, Nitin Samarth
The breaking of time-reversal symmetry by ferromagnetism is predicted to yield profound changes to the electronic surface states in materials known as "topological insulators." We report magnetotransport measurements of a magnetically-doped topological insulator (Mn-Bi2Se3) with a demonstrably suppressed density of surface states at the Dirac point, revealing an intimate connection between ferromagnetism and quantum corrections to the magnetoconductance. These observations are made in samples that are not ideal, with both bulk and surface contributions to electron transport. Nonetheless, our observations are consistent with theoretical predictions that the opening of a gap in the Dirac spectrum drives conductance in topological insulators from the symplectic to the unitary class, suggesting that some aspects of the observed magnetoconductance may indeed originate from surface transport. A concerted interpretation of data obtained from electrical transport, angle-resolved photoemission spectroscopy, superconducting quantum interference device magnetometry, and scanning tunneling microscopy indicates that the ferromagnetism responsible for modifications in the surface states occurs in nanoscale regions on the surface where magnetic atoms segregate during sample growth.
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http://arxiv.org/abs/1206.2908
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