Investigating and manipulating the molecular beam epitaxy growth kinetics of intrinsic magnetic topological insulator MnBi₂Te₄ with in situ angle-resolved photoemission spectroscopy

Abstract

Intrinsic magnetic topological insulator MnBi 2 Te 4 is the key to realizing the quantum anomalous Hall effect and other related quantum phenomena at a sufficiently high temperature for their practical electronic applications. The research progress on the novel material, however, is severely hindered by the extreme difficulty in preparing its high-quality thin films with well-controlled composition and thickness. Combining molecular beam epitaxy (MBE) and in situ angle-resolved photoemission spectroscopy (ARPES), we have systematically studied the growth conditions and kinetics of MnBi 2 Te 4 thin films prepared by simple co-evaporation of Mn, Bi and Te. The transition and competition between the Mn-doped Bi 2 Te 3 and MnBi 2 Te 4 phases under different growth conditions have been mapped in detail, which gives the recipe and principles of growing high-quality MnBi 2 Te 4 thin films. Particularly, to obtain high quality MnBi 2 Te 4 films, it is crucial to raise the growth temperature as high as allowed by the nucleation of the films to minimize density of Mn substitutional atoms on Bi sites. The ARPES data also map the kinetic process in the nucleation and ripening of MnBi 2 Te 4 islands. These results offer the essential information for designing and optimizing the MBE growth procedure of MnBi 2 Te 4 -like compounds to achieve the exotic topological quantum effects.

Epitaxial Growth and Structural Characterizations of MnBi2Te4 Thin Films in Nanoscale

“…This suggests that at a lower Mn/Bi ratio, Mn atoms mainly act as dopants without significantly changing the crystalline structure of Bi2Te3. The trends are consistent with the previous reports [33]. Moreover, compared with the previous study [34], the quartz crystal microbalance (QCM) was used to calibrate the φ , which is different from the calibration by BFM in our study.…”

“…Hence, the MBE growth of high-quality MnBi2Te4 films is essential for the practical development of devices specifically designed to exploit the remarkable properties of the QAH state and axion insulator state. To date, the MBE growth of MnBi2Te4 has been pursued by a few groups [31][32][33][34][35][36][37][38]. Despite great effort, the preparation of high-quality MnBi2Te4 thin films has become a major challenge in this developing field.…”

Tailoring Magnetic Exchange Interactions in Ferromagnet-Intercalated MnBi2Te4 Superlattices

“…Besides, the corresponding anomalous Hall resistance (Rxy) data (Fig. 1e) reaches saturation above Hs with Rs = 4 kΩ, a relatively larger value compared with other reported MBE-grown MBT films 15,26,27 . It is noted that the hybrid-AHE-like Rxy slope at low magnetic fields (± 3.3 T) may be caused by native anti-site defects and/or random stacking order in MBT, which in turn modify the local electronic structures and magnetic moments 22,24,26 .…”

Vapor transport growth of MnBi2Te4 and related compounds

“…The nonstoichiometry of Te and the site mixing between Bi and Te should also be considered depending on the growth conditions. These are confirmed by the experimental observation of lattice defects via single crystal x-ray and neutron diffraction, scanning tunneling microscopy(STM), scanning transmission electron microscopy(STEM) [10][11][12][13][14][15][16][17][18][19][20]. We noticed in our flux-grown MnBi 2 Te 4 crystals, while the concentration of Mn Bi (Mn at Bi site) is in the range of 2-4% in crystals from different batches, the concentration of Bi M n (Bi at Mn site) can vary in a wide range 4-15% which is rather sensitive to growth parameters.…”