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Group IV‐VI van der Waals crystals (MX, where M = Ge, Sn, and X = S, Se) are receiving increasing attention as semiconducting thermoelectric materials with nontoxic, earth‐abundant composition. Among them, SnSe is considered the most promising as it exhibits a remarkably high thermoelectric figure of merit (ZT), initially attributed to its low lattice thermal conductivity. However, it has been shown that the electronic band structure plays an equally important role in thermoelectric performance. A certain band shape, described as a "pudding mold" and characteristic for all MXs, has been predicted to significantly improve ZT by combining good electrical conductivity with high Seebeck coefficient. This subtle feature is explored experimentally for GeS, SnS, and SnSe by means of angle‐resolved photoemission spectroscopy. The technique also allows for the determination of the effective mass and Fermi level position of as‐grown undoped crystals. The findings are supported by ab initio calculations of the electronic band structure. The results greatly contribute to the general understanding of the valence band dispersion of MXs and reinforce their potential as high‐performance thermoelectric materials, additionally giving prospects for designing systems consisting of van der Waals heterostructures. [ABSTRACT FROM AUTHOR]

LaAgSb 2 is a Dirac semimetal showing charge density wave (CDW) order. Previous angle-resolved photoemission spectroscopy (ARPES) results suggest the existence of the Dirac-cone-like structure in the vicinity of the Fermi level along the Γ –M direction. This paper is devoted to a complex analysis of the electronic band structure of LaAgSb 2 by means of ARPES and theoretical studies within the ab initio method as well as tight binding model formulation. To investigate the possible surface states, we performed the direct DFT slab calculation and the surface Green function calculation for the (001) surface. The appearance of the surface states, which depends strongly on the surface, points to the conclusion that LaSb termination is realized in the cleaved crystals. Moreover, the surface states predicted by our calculations at the Γ and X points are found by ARPES. Nodal lines, which exist along the X–R and M–A paths due to crystal symmetry, are also observed experimentally. The calculations reveal other nodal lines, which originate from the vanishing of spin–orbit splitting and are located at the X–M–A–R plane at the Brillouin zone boundary. In addition, we analyze the band structure along the Γ –M path to verify whether Dirac surface states can be expected. Their appearance in this region is not confirmed. [ABSTRACT FROM AUTHOR]

LaCuSb 2 is a superconductor with a transition temperature of about T c = 0.9 K and is a potential platform where Dirac fermions can be experimentally observed. In this paper, we report systematic high-resolution studies of its electronic structure using the angle-resolved photoemission spectroscopy (ARPES) technique supported by the DFT calculation. The Fermi surface consists of four branches, of which the two inner ones are more 3-dimensional and the theoretical calculations reproduce well the experiment. We observe several linear dispersions forming Dirac-like structures. The nodal lines are present in the system along the M–A and X–R and Dirac crossings along the X–R are observed by ARPES. Finally, the nesting between external Fermi surface pockets, which corresponds to charge density wave (CDW) modulation vector is enhanced in LaCuSb 2 as compared to LaAgSb 2 , while CDW appears in the latter system. • Band structure and Fermi surface of LaCuSb 2 superconductor mapped using ARPES and DFT calculations. • Fermi surface consists of four branches and two inner-ones are more 3-dimensional. • A presence of Dirac fermions is manifested by several Dirac crossings, which are found by ARPES and DFT. • A presence of nodal lines along M-A and X-R directions is found theoretically and the latter line is studied by ARPES. • Enhanced Fermi surface nesting is observed in LaCuSb 2 as compared to LaAgSb 2. [ABSTRACT FROM AUTHOR]