No abstract

Kagome magnets provide a fascinating platform for a plethora of topological quantum phenomena, in which the delicate interplay between frustrated crystal structure, magnetization, and spin–orbit coupling (SOC) can engender highly tunable topological states. Here, utilizing angle‐resolved photoemission spectroscopy, the Weyl lines are directly visualized with strong out‐of‐plane dispersion in the A–A stacked kagome magnet GdMn6Sn6. Remarkably, the Weyl lines exhibit a strong magnetization‐direction‐tunable SOC gap and binding energy tunability after substituting Gd with Tb and Li, respectively. These results not only illustrate the magnetization direction and valence counting as efficient tuning knobs for realizing and controlling distinct 3D topological phases, but also demonstrate AMn6Sn6 (A = rare earth, or Li, Mg, or Ca) as a versatile material family for exploring diverse emergent topological quantum responses.

The Sn-induced √ 3 × √ 3 surface reconstruction on Si(111) has been investigated by materialspecific many-body calculations and by angle-resolved photoelectron spectroscopy (ARPES). This triangular surface system in the low adatom coverage regime is governed by rather localized dangling bond orbitals with enhanced electronic correlations and it is prone to exhibit magnetic frustration. We find a rather good overall agreement of the spectral function and its temperature-dependence between theory and experiment. Changes in the ARPES band topology in comparison to the density functional calculations can be explained as a spectral weight redistribution with respect to an additional symmetry which is not due to any geometrical change. This new symmetry corresponds to a magnetic order, which is found to be more complex than the canonical 120 • anti-ferromagnetic order on a triangular lattice with nearest-neighbor coupling only.

No abstract

We present angle-resolved photoemission measurements for ultrathin In films on Si(111). Depending on the coverage, this system self-organizes into a metallic monolayer with either 4x1 or !7x!3 symmetry relative to the substrate. Electronically, they behave like ideal one-and twodimensional electron gases (1DEG and 2DEG), respectively. The 4x1 system has atomic chains of In whose energy bands disperse only parallel to the chains, while for the !7x!3 system, the dominant reciprocal space features (in both diffraction and bandstructure) resemble a pseudosquare lattice with only weaker secondary features relating to the !7x!3 periodicity. In both materials the electrons show coupling to the structure. The 1DEG couples strongly to phonons of momentum 2k F , leading to an 8x"2" Peierls-like insulating ground state. The 2DEG appears to be partially stabilized by electron gap formation at the !7x!3 zone boundary.