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LaCuSb$_{2}$ is a superconductor with a transition temperature of about $T_\text{c} = 0.9$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 ${\text{M}}$-${\text{A}}$ and ${\text{X}}$-${\text{R}}$ and Dirac crossings along ${\text{X}}$-${\text{R}}$ 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.

The magnetic sublayers introduced by intercalation into the host transition-metal dichalcogenide (TMD) are known to produce various magnetic states. The magnetic sublayers and their magnetic ordering strongly modify the electronic coupling between layers of the host compound. Understanding the roots of this variability is a significant challenge. Here we employ the angle-resolved photoelectron spectroscopy at various photon energies, the {\it ab initio} electronic structure calculations, and modeling to address the particular case of Ni-intercalate, Ni$_{1/3}$NbS$_2$. We find that the bands around the Fermi level bear the signature of a strong yet unusual hybridization between NbS$_2$ conduction band states and the Ni 3$d$ orbitals. The hybridization between metallic NbS$_2$ layers is almost entirely suppressed in the central part of the Brillouin zone, including the part of the Fermi surface around the $\mathrm{\Gamma}$ point. Simultaneously, it gets very pronounced towards the zone edges. It is shown that this behavior is the consequence of the rather exceptional, {\it symmetry imposed}, spatially strongly varying, {\it zero total} hybridization between relevant Ni magnetic orbitals and the neighboring Nb orbitals that constitute the metallic bands. We also report the presence of the so-called $\beta$-feature, discovered only recently in two other magnetic intercalates with very different magnetic orderings. In Ni$_{1/3}$NbS$_2$, the feature shows only at particular photon energies, indicating its bulk origin. Common to prior observations, it appears as a series of very shallow electron pockets at the Fermi level, positioned along the edge of the Brillouin zone. Unforeseen by {\it ab initio} electronic calculations, and its origin still unresolved, the feature appears to be a robust consequence of the intercalation of 2H-NbS$_2$ with magnetic ions., Comment: 14 pages, 7 figures with subfigures, 53 references, supplemental material uploaded as the separate pdf file

Fast, reversible, and low-power manipulation of the spin texture is crucial for next generation spintronic devices like non-volatile bipolar memories, switchable spin current injectors or spin field effect transistors. Ferroelectric Rashba semiconductors (FERSC) are the ideal class of materials for the realization of such devices. Their ferroelectric character enables an electronic control of the Rashba-type spin texture by means of the reversible and switchable polarization. Yet, only very few materials have been established to belong to this class of multifunctional materials. Here, Pb1-xGexTe is unraveled as a novel FERSC system down to nanoscale. The ferroelectric phase transition and concomitant lattice distortion is demonstrated by temperature dependent X-ray diffraction, and its effect on electronic properties are measured by angle-resolved photoemission spectroscopy. In few nanometer-thick epitaxial heterostructures, a large Rashba spin-splitting is exhibiting a wide tuning range as a function of temperature and Ge content. Our work defines Pb1- xGexTe as a high-potential FERSC system for spintronic applications., Comment: 18 pages, 6 figures

$\alpha$-Sn is an elemental topological material, whose topological phases can be tuned by strain and magnetic field. Such tunability offers a substantial potential for topological electronics. However, InSb substrates, commonly used to stabilize $\alpha$-Sn allotrope, suffer from parallel conduction, restricting transport investigations and potential applications. Here, the successful MBE growth of high-quality $\alpha$-Sn layers on insulating, hybrid CdTe/GaAs(001) substrates, with bulk electron mobility approaching 20000 cm$^2$V$^{-1}$s$^{-1}$ is reported. The electronic properties of the samples are systematically investigated by independent complementary techniques, enabling thorough characterization of the 3D Dirac (DSM) and Weyl (WSM) semimetal phases induced by the strains and magnetic field, respectively. Magneto-optical experiments, corroborated with band structure modeling, provide an exhaustive description of the bulk states in the DSM phase. The modeled electronic structure is directly observed in angle-resolved photoemission spectroscopy, which reveals linearly dispersing bands near the Fermi level. The first detailed study of negative longitudinal magnetoresistance relates this effect to the chiral anomaly and, consequently, to the presence of WSM. Observation of the $\pi$ Berry phase in Shubnikov-de Haas oscillations agrees with the topologically non-trivial nature of the investigated samples. Our findings establish $\alpha$-Sn as an attractive topological material for exploring relativistic physics and future applications., Comment: Accepted version; Main text: 37 pages, 7 figures; Supplementary Materials: 29 pages, 13 figures

LaAgSb$_{2}$ is a Dirac semimetal showing charge density wave (CDW) order. Previous ARPES results suggest the existence of the Dirac-cone-like structure in the vicinity of the Fermi level along the $\Gamma$-M direction [X. Shi et al., Phys. Rev. B 93, 081105(R) (2016)]. This paper is devoted to a complex analysis of the electronic band structure of LaAgSb$_{2}$ by means of angle-resolved photoemission spectroscopy (ARPES) and theoretical calculations within the direct 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 surface, points to the conclusion that LaSb termination is realized in the cleaved crystals. Moreover, the surface states predicted by our calculations at the $\Gamma$ and $X$ points are found by ARPES. Nodal lines, which exist along X--R and M-A path due to crystal symmetry, are also observed experimentally. The calculations reveal another nodal lines, which originate from vanishing of spin-orbit coupling and are located at X-M-A-R plane at the Brillouin zone boundary. In addition, we analyze band structure along the $\Gamma$-M path to verify, whether Dirac surface states can be expected. Their appearance in this region is not confirmed., Comment: 14 pages, 12 figures, Supplemental Material (4 pages, 5 figures)

Studies of the Fermi surface modification after in-situ covering NbP semimetal with heavy elements Pb and Nb ultrathin layers were performed by means of angle-resolved photoemission spectroscopy (ARPES). First, the electronic structure was investigated for pristine single crystals with two possible terminations (P and Nb) of the (0 0 1) surface. The nature of the electronic states of these two cleaving planes is different: P-terminated surface shows spoon and bow tie shaped fingerprints, whereas these shapes are not present in Nb-terminated surfaces. ARPES studies show that even 1 monolayer (ML) of Pb causes topological quantum Lifshitz transition (TQLT) in P- and Nb-terminated surfaces. Deposited Pb 5d electrons have wide extended atomic orbitals which leads to strong hybridization with Pb-terminated surface and a corresponding shift in the Fermi energy. Nb has less capability to perturb the system than Pb because Nb has weaker spin-orbit coupling than Pb. Nb-terminated surface subjected to surface decoration with approximately 1.3 ML of Nb shows no dramatic modification in the Fermi surface. In the case of Nb decorated P-terminated surface, deposition of approximately 1 ML modifies the electronic structure of NbP and it is on the verge of TQLT. Despite the strong spin-orbit and strong hybridization of the heavy elements on the surface, it is possible to observe the TQLT of the surface states thanks to the robustness of the bulk topology., Comment: 9 Pages, 8 Figures

Co$_{1/3}$NbS$_2$ is the magnetic intercalate of 2H-NbS$_2$ where electronic itinerant and magnetic properties strongly influence each other throughout the phase diagram. Here we report the first angle-resolved photoelectron spectroscopy (ARPES) study in Co$_{1/3}$NbS$_2$. The observed electronic structure seemingly resembles the one of the parent material 2H-NbS$_2$, with the shift in Fermi energy of 0.5 eV accounting for the charge transfer of approximately two electrons from each Co ion into the NbS$_2$ layers. However, we observe significant departures from the 2H-NbS$_2$ rigid band picture: Entirely unrelated to the 2H-NbS$_2$ electronic structure, a shallow electronic band is found crossing the Fermi level near the boundary of the first Brillouin zone of the superstructure imposed by the intercalation. The evolution of the experimental spectra upon varying the incident photon energy suggests the Co origin of this band. Second, the Nb bonding band, found deeply submerged below the Fermi level at the $\Gamma$ point, indicates the interlayer-hybridization being very much amplified by intercalation, with Co magnetic ions probably acting as covalent bridges between NbS$_2$ layers. The strong hybridization between conducting and magnetic degrees of freedom suggests dealing with strongly correlated electron system where the interlayer coupling plays an exquisite role., Comment: 22 pages, 20 figures