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.

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Topological materials host fascinating low dimensional gapless states at the boundary. As a prominent example, helical topological edge states (TESs) of two-dimensional topological insulators (2DTIs) and their stacked three-dimensional (3D) equivalent, weak topological insulators (WTIs), have sparked research enthusiasm due to their potential application in the next generation of electronics/spintronics with low dissipation. Here, we propose layered superconducting material CaSn as a WTI with nontrivial Z2 as well as nodal line semimetal protected by crystalline non-symmorphic symmetry. Our systematic angle-resolved photoemission spectroscopy (ARPES) investigation on the electronic structure exhibits excellent agreement with the calculation. Furthermore, scanning tunnelling microscopy/spectroscopy (STM/STS) at the surface step edge shows signatures of the expected TES. These integrated evidences from ARPES, STM/STS measurement and corresponding ab initio calculation strongly support the existence of TES in the non-symmorphic nodal line semimetal CaSn, which may become a versatile material platform to realize multiple exotic electronic states as well as topological superconductivity.

We report an unusual pressure-induced superconducting state that coexists with an antiferromagnetic ordering of Eu2+ moments and shows a large upper critical field comparable to the Pauli paramagnetic limit in EuTe2. In concomitant with the emergence of superconductivity with Tc ≈ 3–5 K above Pc ≈ 6 GPa, the antiferromagnetic transition temperature TN(P) experiences a quicker rise with the slope increased dramatically from dTN/dP = 0.85(14) K/GPa for P ≤ Pc to 3.7(2) K/GPa for P ≥ Pc. Moreover, the superconducting state can survive in the spin-flop state with a net ferromagnetic component of the Eu2+ sublattice under moderate magnetic fields μ0H ≥ 2 T. Our findings establish the pressurized EuTe2 as a rare magnetic superconductor possessing an intimated interplay between magnetism and superconductivity.

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