Zipporah Rini Benher

Topological semimetals, being characterized by symmetry‐protected band crossings, represent a fascinating class of materials with extraordinary electronic properties. Type‐II Dirac semimetals, featuring highly tilted Dirac cones, offer unique opportunities for both fundamental research and technological advancements. Platinum ditelluride (PtTe ₂ ) has emerged as a promising candidate for a type‐II Dirac semimetal, exhibiting relevant properties for future spintronic and optoelectronic devices. While the existence of type‐II Dirac cones in PtTe ₂ has been confirmed by cryogenic temperature angle‐resolved photoemission spectroscopy (ARPES), practical applications necessitate their stability at ambient conditions. Here, we present a melt growth method for the synthesis of high‐quality PtTe ₂ crystals and we perform ARPES characterization both at cryogenic and at room temperature, providing compelling evidence for the robust nature of its topological electronic structure under realistic operating conditions. This demonstration paves the way for the development of PtTe ₂ ‐based devices leveraging its distinctive topological properties in practical settings.

Magnetic order engineering in two-dimensional Dirac systems is of great interest for theoretical and technological exploration. Up to now, the experimental advances in this field mostly concerned graphene monolayers. Here, we report a comprehensive study of a monolayer-thick germanene-like sheet in contact with gadolinium atoms. Direct observations supported by first-principles calculations reveal the fingerprints of the Dirac fermions in the electronic structure and noncollinear antiferromagnetism. The hybridization of the germanene layer with Gd atoms leads to a large and tunable gap in the Dirac states that carry a nonzero spin-Berry curvature. We discovered that cesium-induced controlled electron doping can switch the system into a ferromagnetic state and then back to the antiferromagnetism at saturated cesium monolayer limit. We explain these reversible magnetic transitions by the oscillatory behavior of the Ruderman-Kittel-Kasuya-Yosida interaction and suggest that this system could find application in magnetoelectronics and spintronics.

Antimonene, the two-dimensional phase of antimony, appears in two distinct allotropes when epitaxially grown on Bi2Se3: the puckered asymmetric washboard (α) and buckled honeycomb (β) bilayer structures. As-deposited antimony films exhibit varying proportions of single α and β structures. We identify the conditions necessary for ordered, pure-phase growth of single to triple β-antimonene bilayers. Additionally, we determine their electronic structure, work function, and characteristic core-level binding energies, offering an explanation for the relatively large chemical shifts observed among the different phases. This study not only establishes a protocol for achieving a single β phase of antimonene but also provides key signatures for distinguishing between the different allotropes using standard spectroscopic and microscopic techniques.

Phase separation from a melt was used as a strategy to obtain diluted Cr-doped Bi ₂ Se ₃ bulk crystals. Large (∼500 μm × 500 μm) and chemically homogeneous Bi _1.993 Cr _0.007 Se ₃ crystals were obtained displaying an energy gap at the Dirac point.

Topological insulators are bulk insulators with metallic and fully spin-polarized surface states displaying Dirac-like band dispersion. Due to spin-momentum locking, these topological surface states (TSSs) have a predominant in-plane spin polarization in the bulk fundamental gap. Here, we show by spin-resolved photoemission spectroscopy that the TSS of a topological insulator interfaced with an antimonene bilayer exhibits nearly full out-of-plane spin polarization within the substrate gap. We connect this phenomenon to a symmetry-protected band crossing of the spin-polarized surface states. The nearly full out-of-plane spin polarization of the TSS occurs along a continuous path in the energy-momentum space, and the spin polarization within the gap can be reversibly tuned from nearly full out-of-plane to nearly full in-plane by electron doping. These findings pave the way to advanced spintronics applications that exploit the giant out-of-plane spin polarization of TSSs.

We investigated the quasi-binary Bi₂Se₃–Bi₂S₃ system and experimentally demonstrated the compositional range of existence of the topological surface states.