Sample-dependent Dirac-point gap in ${\mathrm{MnBi}}_{2}{\mathrm{Te}}_{4}$ and its response to applied surface charge: A combined photoemission and ab initio study

Sample-dependent Dirac-point gap in ${MnBi}_{2} {Te}_{4}$ and its response to applied surface charge: A combined photoemission and ab initio study

A. M. Shikin, D. A. Estyunin, N. L. Zaitsev, D. Glazkova, I. I. Klimovskikh, S. O. Filnov, A. G. Rybkin, E. F. Schwier, S. Kumar, A. Kimura, N. Mamedov, Z. Aliev, M. B. Babanly, K. Kokh, O. E. Tereshchenko, M. M. Otrokov, E. V. Chulkov, K. A. Zvezdin, and A. K. Zvezdin

Phys. Rev. B 104, 115168 – Published 30 September 2021

Abstract

Recently discovered intrinsic antiferromagnetic topological insulator $Mn {Bi}_{2} {Te}_{4}$ presents an exciting platform for realization of the quantum anomalous Hall effect and a number of related phenomena at elevated temperatures. An important characteristic making this material attractive for applications is its predicted large magnetic gap at the Dirac point (DP). However, while the early experimental measurements reported on large DP gaps, a number of recent studies claimed to observe a gapless dispersion of the $Mn {Bi}_{2} {Te}_{4}$ Dirac cone. Here, using micro( $μ$ )-laser angle-resolved photoemission spectroscopy, we study the electronic structure of 15 different $Mn {Bi}_{2} {Te}_{4}$ samples, grown by two different chemists groups. Based on the careful energy distribution curves analysis, the DP gaps between 15 and 65 meV are observed, as measured below the Néel temperature at about 10–16 K. At that, roughly half of the studied samples show the DP gap of about 30 meV, while for a quarter of the samples the gaps are in the 50 to 60 meV range. Summarizing the results of both our and other groups, in the currently available $Mn {Bi}_{2} {Te}_{4}$ samples the DP gap can acquire an arbitrary value between a few and several tens of meV. Furthermore, based on the density functional theory, we discuss a possible factor that might contribute to the reduction of the DP gap size, which is the excess surface charge that can appear due to various defects in surface region. We demonstrate that the DP gap is influenced by the applied surface charge and even can be closed, which can be taken advantage of to tune the $Mn {Bi}_{2} {Te}_{4}$ DP gap size.

Received 2 July 2021
Accepted 13 September 2021

DOI:https://doi.org/10.1103/PhysRevB.104.115168

Physics Subject Headings (PhySH)

Topological insulators

Antiferromagnets Magnetic insulators Topological materials

Ab initio calculations Angle-resolved photoemission spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

A. M. Shikin ^1,*,†, D. A. Estyunin ^1,†, N. L. Zaitsev ², D. Glazkova¹, I. I. Klimovskikh¹, S. O. Filnov¹, A. G. Rybkin ¹, E. F. Schwier³, S. Kumar ³, A. Kimura⁴, N. Mamedov⁵, Z. Aliev^5,6, M. B. Babanly ⁷, K. Kokh^1,8,17, O. E. Tereshchenko^1,9,10, M. M. Otrokov^11,12, E. V. Chulkov^1,13,14, K. A. Zvezdin^15,16, and A. K. Zvezdin^15,16

¹Saint Petersburg State University, 198504 Saint Petersburg, Russia
²Institute of Molecule and Crystal Physics, Ufa Federal Research Center of the Russian Academy of Sciences, 450075, Ufa, Russia
³Hiroshima Synchrotron Radiation Center, Hiroshima University, Hiroshima 739-0046, Japan
⁴Graduate School of Advanced Science and Engineering, Hiroshima University, Hiroshima 739-8526, Japan
⁵Institute of Physics, ANAS, AZ1143 Baku, Azerbaijan
⁶Azerbaijan State Oil and Industry University, AZ1010 Baku, Azerbaijan
⁷Institute of Catalysis and Inorganic Chemistry, ANAS, AZ1143 Baku, Azerbaijan
⁸V.S. Sobolev Institute of Geology and Mineralogy, Novosibirsk, 630090, Russia
⁹A.V. Rzhanov Institute of Semiconductor Physics, Novosibirsk, 630090, Russia
¹⁰Novosibirsk State University, Novosibirsk, 630090, Russia
¹¹Centro de Física de Materiales, Facultad de Ciencias Químicas, UPV/EHU, Apdo. 1072, 20080 San Sebastián, Spain
¹²IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Basque Country, Spain
¹³Donostia International Physics Center (DIPC), 20018 Donostia-San Sebastián, Basque Country, Spain
¹⁴Departamento de Polímeros y Materiales Avanzados: Física, Química y Tecnología, Facultad de Ciencias Químicas, Universidad del País Vasco UPV/EHU, 20080 San Sebastián/Donostia, Basque Country, Spain
¹⁵A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow, 119991, Russia
¹⁶Russian Quantum Center, Skolkovo, 143025, Russia
¹⁷Kemerovo State University, Kemerovo, 650000, Russia

^*ashikin@inbox.ru
^†A.M.S. and D.A.E. contributed equally.

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 104, Iss. 11 — 15 September 2021

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Schematic crystalline structure of the first two SLs in MBT with marked direction and value of magnetic moment on each atom. (b) Calculated electronic structure of surface states in 6 SL MBT slab without applying external charge. The Dirac gap size is 81 meV. The size of circles reflects the degree of localization of the corresponding wave function within the first SL. The gray areas mark the bulk bands projected onto the surface Brillouin zone.
Reuse & Permissions
Figure 2
(a) ARPES dispersion relations measured at $h ν = 6.3$ eV with $s$ -polarized LR below $Mn {Bi}_{2} {Te}_{4}$ (10–16 K) for MBT samples with large, medium, and small Dirac gaps and their the second derivatives $d^{2} N / d E^{2}$ in (b). (c) EDCs cut at the $Γ$ point ( $k_{∥} = 0$ Å $^{- 1}$ )—red curves and some $\pm k_{∥}$ green curves. Position of the cuts are marked with lines of corresponding color in (a) and (b). Spectral components decomposition are shown for EDCs cut at the $Γ$ point. Red peaks correspond to the Dirac cone states, black peaks to the Te $p_{z}$ exchange-split states. Additional peaks that are out of interest are gray. (d) Dependence of the splitting between the top and bottom Dirac cone states on wave vector ( $k_{∥}$ ). Dots (connected with lines) show experimental values of splitting, black curve is fitting function of the gapped cone (see text). (e) The DP gap sizes of all 15 MBT samples presented in this paper. Orange (red) bars correspond to the samples whose spectra are presented in Fig. 2 (see the Supplemental Material Figs. 1S–3S [61]). Samples from the Novosibirsk group are marked by black triangles, while the rest of the samples have been grown in Baku.
Reuse & Permissions
Figure 3
(a) and (b) ARPES dispersion relations measured for MBT below (10 K) and above $T_{N}$ (35 K) for samples with the different Dirac gap values in the $d^{2} N / d E^{2}$ presentation for better visualization of the features. (c) and (d) EDCs at 10 K (blue curves) and 35 K (red curves) cut at the $Γ$ point ( $k_{∥} = 0$ Å $^{- 1}$ ) with decomposition to spectral components: solid line peaks of corresponding color—the Dirac cone states, black and green peaks—Te $p_{z}$ states, gray peaks VB and CB states. (e) and (f) The modifications (as $d^{2} N / d E^{2}$ ) of the states at the $Γ$ point under permanent growth of temperature from 10 to 35 K (step $Δ T = 1.5$ and 0.5 K). Red and white (magenta) curves are guide to the eye temperature variation of Te $p_{z}$ and the Dirac cone states, respectively. Vertical half-transparent line marks onset temperature of Te $p_{z}$ splitting.
Reuse & Permissions
Figure 4
(a)–(e) Spin-resolved calculated dispersion relations with various applied charges to the sample surface. Left and right panels show out-of-plane ( $+ S_{z}$ red and $- S_{z}$ blue) and in-plane ( $+ S_{x, y}$ red and $- S_{x, y}$ blue) spin components, size of circles matches the value of spin-vector projection. The DC state is roughly highlighted with brighter colors. (f) The change of the Dirac gap value plotted depending on the surface charge (bottom axis) and the surface potential gradient (top axis).
Reuse & Permissions
Figure 5
Spatial density distribution along $z$ axis of the top (a) and bottom (b) parts of the DC taken at the $Γ$ point for various applied charges $q = - 0.045 e_{0}$ (red), $0 e_{0}$ (blue), and $+ 0.03 e_{0}$ (green). Weight of the upper (lower) part of TSS in each SL is shown by numbers of corresponding color. Left part of (c) spatial distribution of magnetic moments on MBT atoms for various applied charges presented as $[Δ M (z, q) = M (z, q) - M (z, 0)]$ . Color represents value of $Δ M (z, q)$ , horizontal lines mark positions of profiles shown in right part of (c).
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Sample-dependent Dirac-point gap in ${MnBi}_{2} {Te}_{4}$ and its response to applied surface charge: A combined photoemission and ab initio study

A. M. Shikin, D. A. Estyunin, N. L. Zaitsev, D. Glazkova, I. I. Klimovskikh, S. O. Filnov, A. G. Rybkin, E. F. Schwier, S. Kumar, A. Kimura, N. Mamedov, Z. Aliev, M. B. Babanly, K. Kokh, O. E. Tereshchenko, M. M. Otrokov, E. V. Chulkov, K. A. Zvezdin, and A. K. Zvezdin

Phys. Rev. B 104, 115168 – Published 30 September 2021

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

Supplemental Material (Subscription Required)

References (Subscription Required)

Issue

Access Options

Physical Review B

covering condensed matter and materials physics

Sample-dependent Dirac-point gap in MnBi2Te4 and its response to applied surface charge: A combined photoemission and ab initio study

A. M. Shikin, D. A. Estyunin, N. L. Zaitsev, D. Glazkova, I. I. Klimovskikh, S. O. Filnov, A. G. Rybkin, E. F. Schwier, S. Kumar, A. Kimura, N. Mamedov, Z. Aliev, M. B. Babanly, K. Kokh, O. E. Tereshchenko, M. M. Otrokov, E. V. Chulkov, K. A. Zvezdin, and A. K. Zvezdin

Phys. Rev. B 104, 115168 – Published 30 September 2021

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

Supplemental Material (Subscription Required)

References (Subscription Required)

Issue

Access Options

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Sample-dependent Dirac-point gap in ${MnBi}_{2} {Te}_{4}$ and its response to applied surface charge: A combined photoemission and ab initio study