Study of Ho-doped Bi2Te3 topological insulator thin films

Harrison, S. E.; Collins-McIntyre, L. J.; Zhang, S. L.; Baker, Alexander A.; Figueroa, A. I.; Kellock, A. J.; Pushp, Aakash; Chen, Y. L.; Parkin, S. S. P.; Harris, James S.; Laan, G. van der; Hesjedal, T.

doi:10.1063/1.4935235

Cited by 27 publications

(53 citation statements)

References 38 publications

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“…The higher doping concentration samples, on the other hand, are oxidized to a large degree. Note that these samples are structurally of a slightly lower quality13282931. It appears that these crystalline imperfections, or the occurrence of accompanying strain, promote oxidation over time.…”

Section: Resultsmentioning

confidence: 98%

“…The lower doping concentration samples have been successfully cleaved in ultra-high vacuum, following an in-air transfer, and the TSS has been successfully recovered12272931. The higher doping concentration samples, on the other hand, are oxidized to a large degree.…”

Section: Resultsmentioning

confidence: 99%

“…A detailed exposition of the growth process, structural and magnetic studies can be found elsewhere for Gd [refs 12 and 13], Dy [refs 28 and 31], and Ho [ref. 29], respectively. Note that the Gd-doped films were grown in a Se-free MBE system, whereas the Dy- and Ho-doped films show unintentional Se doping of up to 5 at.% due to elevated temperatures in the chamber during growth.…”

Section: Methodsmentioning

confidence: 99%

“…Figure 1 illustrates the layered structure of the crystal, with five atomic layers (Te–Bi–Te–Bi–Te) as a basic unit, known as a quintuple layer (QL). Bi 2 (Se, Te) 3 thin films, doped with the RE elements Gd, Dy, and Ho, as described in detail in refs 13, 28 and 29, were grown by MBE on c -plane sapphire. Below a critical atomic percentage (at.% RE doping), the films were stoichiometric compounds with a 2:3 ratio of Bi and RE to Te (and Se, see Methods section for details).…”

Section: Comparison Of the Structural And Magnetic Propertiesmentioning

confidence: 99%

“…The effective magnetic saturation moments for the 4 f electrons of the Gd, Dy, and Ho doped TIs, as determined by x-ray magnetic circular dichroism (XMCD) at the M 4,5 edges in an applied out-of-plane field, are listed in Table 2 (refs 13, 28 and 29), together with the theoretical values for the LS -coupled atomic ground states. The temperature-dependent XMCD plots reveal paramagnetic behaviour down to the lowest probed temperature of ~2 K. Table 2 shows that saturated moments obtained by XMCD at high field and near liquid He temperatures are 40–50% of the theoretical maximum values.…”

Section: Comparison Of the Structural And Magnetic Propertiesmentioning

confidence: 99%

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Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films

Figueroa

Laan

Harrison

et al. 2016

Sci Rep

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The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi3+ in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the low-doping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Comparison Of the Structural And Magnetic Propertiesmentioning

confidence: 99%

Section: Comparison Of the Structural And Magnetic Propertiesmentioning

confidence: 99%

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Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films

Figueroa

Laan

Harrison

et al. 2016

Sci Rep

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The Material Efforts for Quantized Hall Devices Based on Topological Insulators

Fei

Zhang

et al. 2019

Advanced Materials

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A topological insulator (TI) is a kind of novel material hosting a topological band structure and plenty of exotic topological quantum effects. Achieving quantized electrical transport, including the quantum Hall effect (QHE) and the quantum anomalous Hall effect (QAHE), is an important aspect of realizing quantum devices based on TI materials. Intense efforts are made in this field, in which the most essential research is based on the optimization of realistic TI materials. Herein, the TI material development process is reviewed, focusing on the realization of quantized transport. Especially, for QHE, the strategies to increase the surface transport ratio and decrease the threshold magnetic field of QHE are examined. For QAHE, the evolution history of magnetic TIs is introduced, and the recently discovered magnetic TI candidates with intrinsic magnetizations are discussed in detail. Moreover, future research perspectives on these novel topological quantum effects are also evaluated.

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Magnetic Topological Insulator Heterostructures: A Review

Liu

Hesjedal

2021

Advanced Materials

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Chern number corresponds to the occupancy of discrete Landau levels, which can be varied by tuning the Fermi energy via a gate voltage. It further corresponds to the number of dissipationless conduction channels in the gapless edge state of the quantum Hall insulator that is insulating in the bulk in high magnetic fields.After observing the quantum version of the Hall effect, the natural question to ask is if there is also a quantized version of the anomalous Hall effect (AHE), commonly observed in ferromagnets. This quantum anomalous Hall effect (QAHE) would then be observable in the absence of external fields. The QAHE was initially proposed to arise in 2D honeycomb or kagome lattices, such as monolayer graphene, that host a non-zero out-of-plane magnetic flux density, but zero net flux in each unit cell. [8,9] Later, it was also proposed that the QAHE may be found in Hg 1−y Mn y Te quantum wells without an external magnetic field, in which the effect arises purely due to the spin polarization of the Mn atoms. [10] However, the experimental realization of the QAHE was not reported until 2013, when transport in 3D topological insulators (TIs) doped with magnetic impurities was studied. TIs refer to a class of materials that is insulating in the bulk, but which possess topologically protected conducting surface states. Right from the start, the field was (see refs. [6,11-17]), and continues to be (see refs. [18-20]), to a large degree driven by theory. Common examples of 3D TIs are rhombohedral Bi 2 Se 3 , Bi 2 Te 3 , and Sb 2 Te 3 . [15] The surface state of a TI consists of two linearly dispersing states connecting the bulk conduction and valence bands. The two states cross at one point in reciprocal space, the Dirac point (Figure 1a). The charge carriers in this band structure are massless fermions, which are described by the relativistic Dirac equation. [15] Due to the strong spin-orbit coupling (SOC) in these materials, surface electron spins are locked to their momentum, forming dissipationless, counter-propagating conduction channels in the surface state.By introducing magnetism to a TI, either by impurity doping with magnetic elements, by proximity coupling to a magnetic insulators (MIs), or other magnetic layers, time-reversal symmetry (TRS) can be broken. TRS breaking can induce a bandgap in the surface states, leading to the realization of the QAHE which is characterized by 1D chiral edge conduction in zerofield at remanence, as shown in Figure 1. The Chern number, here being +1 or -1, corresponds to the direction of the spinmomentum locked edge current that can be flipped by a (small) external field. Using first-principles calculations, Sb 2 Te 3 , Bi 2 Te 3 , Topological insulators (TIs) provide intriguing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counterpropagating conduction channels in the surface state. The combination of topological properties and magnetic order can lead to new quantum states including the quantum anomalous Hall effect th...

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Study of Ho-doped Bi2Te3 topological insulator thin films

Cited by 27 publications

References 38 publications

Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films

Oxidation Effects in Rare Earth Doped Topological Insulator Thin Films

The Material Efforts for Quantized Hall Devices Based on Topological Insulators

Magnetic Topological Insulator Heterostructures: A Review

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