Tailoring tricolor structure of magnetic topological insulator for robust axion insulator

Mogi, Masataka; Kawamura, Minoru; Tsukazaki, Atsushi; Yoshimi, Ryutaro; Takahashi, Kei; Kawasaki, Masashi; Tokura, Y.

doi:10.1126/sciadv.aao1669

Cited by 200 publications

(162 citation statements)

References 35 publications

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“…Our results thus support recent theoretical predictions that magnetic gaps in topological insulators can be significantly enhanced in multi-layered systems [11]. These are considered as a basis for the realization of new topological phases such as the axion insulator state exhibiting quantized magnetoelectric effects [14,38] and the chiral Majorana fermion [39]. No magnetic gap is detected for Mndoped Bi 2 Se 3 within the experimental resolution but instead, a very large non-magnetic gap that does not increase even when cooling down to 1 K, well below T C , and thus does not have a magnetic contribution.…”

Section: Discussionsupporting

confidence: 88%

Large magnetic gap at the Dirac point in Bi2Te3/MnBi2Te4 heterostructures

Rienks

Wimmer

Sánchez-Barriga

et al. 2019

Nature

236

167

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Magnetically doped topological insulators enable the quantum anomalous Hall effect (QAHE) which provides quantized edge states for lossless charge transport applications [1][2][3][4][5][6][7][8][9]. The edge states are hosted by a magnetic energy gap at the Dirac point[2] but all attempts to observe it directly have been unsuccessful. The size of this gap is considered the clue to overcoming the present limitations of the QAHE, which so far occurs only at temperatures one to two orders of magnitude below its principle limit set by the ferromagnetic Curie temperature T C [8,9]. Here, we use low temperature photoelectron spectroscopy to unambiguously reveal the magnetic gap of Mn-doped Bi 2 Te 3 films which is present only below T C . Surprisingly, the gap turns out to be ∼ 90 meV wide, which not only exceeds k B T at room temperature but is also 5 times larger than predicted by density functional theory [10]. By an exhaustive multiscale structure characterization we show that this enhancement is due to a remarkable structure modification induced by Mn doping. Instead of a disordered impurity system, it forms an alternating sequence of septuple and quintuple layer blocks, where Mn is predominantly incorporated in the center of the septuple layers. This self-organized heterostructure substantially enhances the wave-function overlap and the size of the magnetic gap at the Dirac point, as recently predicted [11]. Mn-doped Bi 2 Se 3 forms a similar heterostructure, however, only a large, albeit nonmagnetic gap is formed. We explain both differences based on the higher spin-orbit interaction in Bi 2 Te 3 with the most important consequence of a magnetic anisotropy perpendicular to the films, whereas for Bi 2 Se 3 the spin-orbit interaction it is too weak to overcome the dipole-dipole interaction. Our findings provide crucial insights for pushing the lossless transport properties of topological insulators towards room-temperature applications.We thank B. Henne, F. Wilhelm, and A. Rogalev for support of the XANES and EX-AFS measurements at ID 12 and BM23 beam lines of the ESRF, V. Holý for advices on the structure model, W. Grafeneder for the TEM sample preparation and G. Bihlmayer and A. Ernst for helpful discussions. S.A.K and J.M. are grateful for support from CEDAMNF (CZ.02.1.01/0.0/0.0/15 003/0000358) of Czech ministry MSMT.

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Section: Discussionsupporting

confidence: 88%

Large magnetic gap at the Dirac point in Bi2Te3/MnBi2Te4 heterostructures

Rienks

Wimmer

Sánchez-Barriga

et al. 2019

Nature

236

167

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“…The difficulty in attaining this requirement in modulation-doped TI films in which the two layers are both Cr doped renders the C = 0 state to be significantly more fragile than the counterpart C = ±1 states. Very recently, two independent studies 38,39 have attained much larger ΔH c by doping one layer by Cr and the other layer by V leading to a significantly more robust ZHP providing strong support to this conclusion. Control of the materials properties in terms of doping homogeneity, enlarging the size and the uniformity of the SPM islands, and increasing the difference in the coercive fields of the top and bottom magnetically doped layers thus emerges as the key challenge for attaining robust QAH and axion states and extending their temperature range for novel electronic applications.…”

Section: Resultsmentioning

confidence: 81%

Observation of superparamagnetism in coexistence with quantum anomalous Hall C = ±1 and C = 0 Chern states

et al. 2017

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Simultaneous transport and scanning nanoSQUID-on-tip magnetic imaging studies in Cr-(Bi,Sb) 2 Te 3 modulation-doped films reveal the presence of superparamagnetic order within the quantum anomalous Hall regime. In contrast to the expectation that a longrange ferromagnetic order is required for establishing the quantum anomalous Hall state, superparamagnetic dynamics of weakly interacting nanoscale magnetic islands is observed both in the plateau transition regions, as well as within the fully quantized C = ±1 Chern plateaus. Modulation doping of the topological insulator films is found to give rise to significantly larger superparamagnetic islands as compared to uniform magnetic doping, evidently leading to enhanced robustness of the quantum anomalous Hall effect. Nonetheless, even in this more robust quantum state, attaining full quantization of transport coefficients requires magnetic alignment of at least 95% of the superparamagnetic islands. The superparamagnetic order is also found within the incipient C = 0 zero Hall plateau, which may host an axion state if the top and bottom magnetic layers are magnetized in opposite directions. In this regime, however, a significantly lower level of island alignment is found in our samples, hindering the formation of the axion state. Comprehension and control of superparamagnetic dynamics is thus a key factor in apprehending the fragility of the quantum anomalous Hall state and in enhancing the endurance of the different quantized states to higher temperatures for utilization of robust topological protection in novel devices. 1-3 In the QH state the TRSB is induced by high magnetic field applied perpendicular to a high-mobility 2D electron gas. The QAH state, in contrast, can be formed in thin films of topological insulators (TI) even in the absence of magnetic field.3-10 In this case the TRSB is induced by magnetic order attained by doping the TIs with transition metal elements like Cr, V, or Mn,

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“…From the perspective of material science, it is of crucial importance to develop material systems with the coexistence of magnetism and topology that spontaneously breaks the time-reversal symmetry. Most current works tried to introduce magnetism into topological materials extrinsically by doping magnetic impurities [13][14][15][16][17][18] . However, the extrinsic magnetic defects are difficult to control experimentally, which hinders the progress in subsequent applications, for instance, dissipationless electric transportation in quantum anomalous Hall device and topological quantum computation 1,2 .…”

Section: Introductionmentioning

confidence: 99%

Antiferromagnetic topological insulator MnBi₂Te₄: synthesis and magnetic properties

Liu

et al. 2020

Phys. Chem. Chem. Phys.

108

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Recently, MnBi2Te4 has been discovered as the first intrinsic antiferromagnetic topological insulator (AFM TI), and will become a promising material to discover exotic topological quantum phenomena. In this work, we have realized the successful synthesis of high-quality MnBi2Te4 single crystals by solid-state reactions. The as-grown MnBi2Te4 single crystal exhibits a van der Waals layered structure, which is composed of septuple Te-Bi-Te-Mn-Te-Bi-Te sequences as determined by powder X-ray diffraction (PXRD) and high-resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The magnetic order below 25 K as a consequence of A-type antiferromagnetic interaction between Mn layers in the MnBi2Te4 crystal suggests the unique interplay between antiferromagnetism and topological quantum states. The transport measurements of MnBi2Te4 single crystals further confirm its magnetic transition. Moreover, the unstable surface of MnBi2Te4, which is found to be easily oxidized in air, deserves attention for onging research on few-layer samples. This study on the first AFM TI of MnBi2Te4 will guide the future research on other potential candidates in the MBixTey family (M = Ni, V, Ti, etc.).

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Tailoring tricolor structure of magnetic topological insulator for robust axion insulator

Abstract: Gigantic magnetoresistance is shown in a Cr- and V-doped topological insulator multilayer, assuring robust axion insulator.

Cited by 200 publications

References 35 publications

Large magnetic gap at the Dirac point in Bi2Te3/MnBi2Te4 heterostructures

Large magnetic gap at the Dirac point in Bi2Te3/MnBi2Te4 heterostructures

Observation of superparamagnetism in coexistence with quantum anomalous Hall C = ±1 and C = 0 Chern states

Antiferromagnetic topological insulator MnBi₂Te₄: synthesis and magnetic properties

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Tailoring tricolor structure of magnetic topological insulator for robust axion insulator

Abstract: Gigantic magnetoresistance is shown in a Cr- and V-doped topological insulator multilayer, assuring robust axion insulator.

Cited by 200 publications

References 35 publications

Large magnetic gap at the Dirac point in Bi2Te3/MnBi2Te4 heterostructures

Large magnetic gap at the Dirac point in Bi2Te3/MnBi2Te4 heterostructures

Observation of superparamagnetism in coexistence with quantum anomalous Hall C = ±1 and C = 0 Chern states

Antiferromagnetic topological insulator MnBi2Te4: synthesis and magnetic properties

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Antiferromagnetic topological insulator MnBi₂Te₄: synthesis and magnetic properties