Journal
PHYSICAL REVIEW B
Volume 86, Issue 20, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.86.205127
Keywords
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Funding
- DARPA [N66001-11-1-4110]
- ONR [N00014-12-1-0116, N00014-12-1-0117]
- Penn State Center for Nanoscale Science under the MRSEC program (NSF) [DMR-0820404]
- Pennsylvania State University Materials Research Institute Nanofabrication Laboratory
- National Science Foundation [ECS-0335765]
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [0801388] Funding Source: National Science Foundation
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [0801406] Funding Source: National Science Foundation
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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 15 K <= 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 less than or similar to 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.
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