Interplay between ferromagnetism, surface states, and quantum corrections in a magnetically doped topological insulator

Duming Zhang, Anthony Richardella, David W. Rench, Su Yang Xu, 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

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Abstract

The breaking of time-reversal symmetry by ferromagnetism is predicted to yield profound changes to the electronic surface states of a topological insulator. Here, we report on a concerted set of structural, magnetic, electrical, and spectroscopic measurements of Mn-Bi2Se3 thin films wherein photoemission and x-ray magnetic circular dichroism studies have recently shown surface ferromagnetism in the temperature range 15K≤T≤100 K, accompanied by a suppressed density of surface states at the Dirac point. Secondary-ion mass spectroscopy and scanning tunneling microscopy reveal an inhomogeneous distribution of Mn atoms, with a tendency to segregate towards the sample surface. Magnetometry and anisotropic magnetoresistance measurements are insensitive to the high-temperature ferromagnetism seen in surface studies, revealing instead a low-temperature ferromagnetic phase at T ≲5 K. The absence of both a magneto-optical Kerr effect and an anomalous Hall effect suggests that this low-temperature ferromagnetism is unlikely to be a homogeneous bulk phase but likely originates in nanoscale near-surface regions of the bulk where magnetic atoms segregate during sample growth. Although the samples are not ideal, with both bulk and surface contributions to electron transport, we measure a magnetoconductance whose behavior is qualitatively consistent with predictions that the opening of a gap in the Dirac spectrum drives quantum corrections to the conductance in topological insulators from the symplectic to the orthogonal class.

Original languageEnglish (US)
Article number205127
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume86
Issue number20
DOIs
StatePublished - Nov 26 2012

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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    Zhang, D., Richardella, A., Rench, D. W., Xu, S. Y., Kandala, A., Flanagan, T. C., Beidenkopf, H., Yeats, A. L., Buckley, B. B., Klimov, P. V., Awschalom, D. D., Yazdani, A., Schiffer, P., Hasan, M. Z., & Samarth, N. (2012). Interplay between ferromagnetism, surface states, and quantum corrections in a magnetically doped topological insulator. Physical Review B - Condensed Matter and Materials Physics, 86(20), [205127]. https://doi.org/10.1103/PhysRevB.86.205127