Topological Insulator Thin Films and Heterostructures: Epitaxial Growth, Transport, and Magnetism

Richardella, Anthony; Kandala, Abhinav; Samarth, N.

doi:10.1002/9783527681594.ch12

Cited by 3 publications

(6 citation statements)

References 118 publications

(169 reference statements)

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“…This is consistent with other reports of coexisting hole-mediated and van Vleckmediated ferromagnetism in moderately Cr-doped (Bi,Sb) 2 Te 3[33,34]. Notably, the values of H C extracted from AHE and MOKE measurements correspond well in the absence of a gate effect, but at higher voltages (or UV exposures), MOKE hysteresis measurements indicate a larger H C…”

supporting

confidence: 91%

“…H C decreases by ≈ 30% with increasing V g (or previous exposure to UV light), consistent with only partially hole-mediated ferromagnetism. This is consistent with other reports of coexisting hole-mediated and van Vleckmediated ferromagnetism in moderately Cr-doped (Bi,Sb) 2 Te 3[33,34]. Notably, the values of H C extracted from AHE and MOKE measurements correspond well in the absence of a gate effect, but at higher voltages (or UV exposures), MOKE hysteresis measurements indicate a larger H C than AHE hysteresis measurements.…”

supporting

confidence: 91%

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Local optical control of ferromagnetism and chemical potential in a topological insulator

Yeats

Mintun

Pan

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Many proposed experiments involving topological insulators (TIs) require spatial control over time-reversal symmetry and chemical potential. We demonstrate reconfigurable micron-scale optical control of both magnetization (which breaks time-reversal symmetry) and chemical potential in ferromagnetic thin films of Cr-(Bi,Sb) 2 Te 3 grown on SrTiO 3 . By optically modulating the coercivity of the films, we write and erase arbitrary patterns in their remanent magnetization, which we then image with Kerr microscopy. Additionally, by optically manipulating a space charge layer in the underlying SrTiO 3 substrates, we control the local chemical potential of the films. This optical gating effect allows us to write and erase p-n junctions in the films, which we study with photocurrent microscopy. Both effects are persistent and may be patterned and imaged independently on a few-micron scale. Dynamic optical control over both magnetization and chemical potential of a TI may be useful in efforts to understand and control the edge states predicted at magnetic domain walls in quantum anomalous Hall insulators.topological insulators | ferromagnetism | Kerr microscopy | magneto-optical recording | photocurrent microscopy T he unusual topology of electronic bands in some materials can produce quantum states that are stabilized by symmetry. Topological insulators (TIs) have attracted particular attention for their symmetry-protected surface and edge states, which may hold promise for applications in spintronics and quantum computing (1, 2). Ferromagnetic TIs combine a topologically nontrivial band structure with ferromagnetism, which intrinsically breaks time-reversal symmetry (TRS) and therefore may produce unusual electromagnetic phenomena such as the topological magnetoelectric effect (3, 4), quantized Kerr and Faraday rotation (5, 6), and quantization of the anomalous Hall effect (QAHE) (7,8). However, while the quantum states in an ideal TI are protected by symmetry, most topologically nontrivial materials have proven difficult to grow and engineer. In particular, residual bulk conductivity, and the tendency of TI materials to degrade during semiconductor processing, have impeded many experimental efforts (9-11). Harnessing the unique physics of these materials will require better understanding and control of their magnetism and disorder, as well as methods to engineer TI devices without degrading the properties that make these materials unique.A major challenge in TI research is to identify systems in which the energies and symmetries of TI physics can be reliably controlled in the laboratory. For instance, a criterion for the QAH insulator state is for the chemical potential of electrons µ to lie within an energy gap ∆ in the surface state dispersion, where ∆ ∝ | M ·n|, M is the local magnetization andn is the surface normal (1, 2). At the edges of a uniformly magnetized film, the top and bottom surfaces meet and therefore M ·n changes sign, causing ∆ to vanish. In sufficiently thin films, the vanishing gap produces 1D co...

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supporting

confidence: 91%

supporting

confidence: 91%

Local optical control of ferromagnetism and chemical potential in a topological insulator

Yeats

Mintun

Pan

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Heterostructures of topological insulators with ferromagnetic insulators, such as Bi 2 Se 3 /EuS, (Bi,Sb) 2 Te 3 /GdN, Bi 2 Se 3 /YIG or Bi 2 Se 3 /Cr 2 Ge 2 Te 4 , break time-reversal symmetry while still preserving topological symmetry [Wei et al ., 2013; Yang et al ., 2013; Kandala et al ., 2013; Richardella et al ., 2015; Lang et al ., 2014; Alegria et al ., 2014]. Ideally, transport in such bilayers would be entirely carried by the Dirac surface, modified by exchange coupling with the ferromagnetic layer.…”

Section: Spin Transport At and Through Interfacesmentioning

confidence: 99%

“…Diagrammatic calculations show that an unperturbed Dirac surface state should exhibit weak antilocalization, while opening of a gap would yield weak localization [Lu et al ., 2011]. Indeed, Bi 2 Se 3 and (Bi,Sb) 2 Te 3 layers capped by a ferromagnetic layer of GdN show suppression of weak antilocalization [Kandala et al ., 2013; Richardella et al ., 2015], while Bi 2 Se 3 /EuS bilayers show a transition to weak localization [Yang et al ., 2013]. Anomalous Hall effect and polarized neutron reflectometry in Bi 2 Se 3 /EuS [Wei et al ., 2013; Katmis et al ., 2016], and magneto-optical Kerr effect and magnetoresistance of Bi 2 Se 3 /YIG [Lang et al ., 2014] suggest a proximity-induced ferromagnetism in the topological insulator, implying broken time-reversal in the topological insulator surface-derived states resulting from the proximate ferromagnetic insulator.…”

Section: Spin Transport At and Through Interfacesmentioning

confidence: 99%

Interface-induced phenomena in magnetism

et al. 2017

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This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially-driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange spring magnets, spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and non-collinear spin textures, non-linear dynamics including spin torque transfer and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.

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“…blocks for unconventional computing paradigms. Figure 1 shows schematically the system configuration of two FMIs deposited on the top of a TI 67,68 (Appendix A provides more details about possible experimental realization.) The dynamical variable of each FMI is its macroscopic magnetization vector M .…”

Section: Introductionmentioning

confidence: 99%

Phase Locking of a Pair of Ferromagnetic Nano-oscillators on a Topological Insulator

Wang

Rizzo

et al. 2018

Phys. Rev. Applied

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We investigate the magnetization dynamics of a pair of ferromagnetic insulators (FMIs) deposited on the surface of a topological insulator (TI). Due to the nonlinear nature of the underlying physics and intrinsic dynamics, the FMIs can exhibit oscillatory behaviors even under a constant applied voltage. The motion of the surface electrons of the TI, which obeys relativistic quantum mechanics, provides a mechanism of direct coupling between the FMIs. In particular, the spin polarized current of the TI surface electrons can affect the magnetization of the two FMIs, which in turn modulates the electron transport, giving rise to a hybrid relativistic quantum/classical nonlinear dynamical system. We find robust phase and anti-phase locking between the magnetization dynamics. As driving the surface electrons of a TI only requires extremely low power, our finding suggests that nano FMIs coupled by a spin polarized current on the surface of TI have the potential to serve as the fundamental building blocks of unconventional, low-power computing paradigms. arXiv:1811.05551v1 [cond-mat.mes-hall]

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Topological Insulator Thin Films and Heterostructures: Epitaxial Growth, Transport, and Magnetism

Cited by 3 publications

References 118 publications

Local optical control of ferromagnetism and chemical potential in a topological insulator

Local optical control of ferromagnetism and chemical potential in a topological insulator

Interface-induced phenomena in magnetism

Phase Locking of a Pair of Ferromagnetic Nano-oscillators on a Topological Insulator

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