Approaching a Minimal Topological Electronic Structure in Antiferromagnetic Topological Insulator MnBi₂Te₄ via Surface Modification

Abstract

The topological electronic structure plays a central role in the nontrivial physical properties in topological quantum materials. A minimal, "hydrogen-atom-like" topological electronic structure is desired for research. In this work, we demonstrate an effort toward the realization of such a system in the intrinsic magnetic topological insulator MnBi 2 Te 4 , by manipulating the topological surface state (TSS) via surface modification. Using high resolution laser-and synchrotron-based angle-resolved photoemission spectroscopy (ARPES), we found the TSS in MnBi 2 Te 4 is heavily hybridized with a trivial Rashba-type surface state (RSS), which could be efficiently removed by the in situ surface potassium (K) dosing. By employing multiple experimental methods to characterize K dosed surface, we attribute such a modification to the electrochemical reactions of K clusters on the surface. Our work not only gives a clear band assignment in MnBi 2 Te 4 but also provides possible new routes in accentuating the topological behavior in the magnetic topological quantum materials.

Interplay between exchange split Dirac and Rashba-type surface states in MnBi$_2$Te$_4$/BiTeI interface

“…The latter features are the source of intrinsic Hall conductivity, due to timereversal symmetry breaking, what allows applying this state in spintronic devices. This finding demonstrates another way to form hybridization gap between Rashbatype state and Dirac cone state, which also previously observed in pristine MBT [22] and MnBi 6 Te 10 [23] surfaces.…”

Evolution of the Electronic Structure of Ultrathin MnBi2Te4 Films

“…Despite the drastic difference in the pristine samples (Figure and Figure ), the band structure of the film with K coverage of 0.15 ML is very similar to the pristine bulk sample, providing the compelling evidence that the kink is from the interaction between the RSB and TSSs. Moreover, the band structure of bulk MnBi 2 Te 4 eventually becomes similar to that of the films, leaving only the BVB, BCB, and TSSs with a diminishing gap (Figure f and Figure h) . The overall evolution of the band structure of the bulk sample also shows a nonmonotonic shift with surface K doping.…”

“…Again, the TSSs above the kink and the RSB show similar spectral weight and broadening. Moreover, with further doping, the RSB and the kink synchronously shift toward E F (Figure d) and gradually disappear at heavy doping level (>0.15 ML, see Figure S9a), clearly suggesting their common origin.…”

“…Moreover, the band structure of bulk MnBi 2 Te 4 eventually becomes similar to that of the films, leaving only the BVB, BCB, and TSSs with a diminishing gap (Figure 4f and Figure 4h). 45 The overall evolution of the band structure of the bulk sample also shows a nonmonotonic shift with surface K doping. As shown in Figure S9b, the RSB, the BCB, and the BVB first shift toward higher binding energies, then gradually shift back toward E F , 45 similar to the evolution of the band structure of the films in Figure 3.…”

“…45 The overall evolution of the band structure of the bulk sample also shows a nonmonotonic shift with surface K doping. As shown in Figure S9b, the RSB, the BCB, and the BVB first shift toward higher binding energies, then gradually shift back toward E F , 45 similar to the evolution of the band structure of the films in Figure 3. The observed nonmonotonic shift of the band structure, however, is beyond the expectation of the simple electrondonating picture, although it has been observed in different materials.…”