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Register a new userThree-dimensional band structure of layered TiTe2: Photoemission final-state effects
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Three-dimensional band structure of unoccupied and occupied states of the prototype layered material TiTe2 is determined focusing on the GammaA line of the Brillouin zone. Dispersions and lifetimes of the unoccupied states, acting as the final states in the photoemission process, are determined from a very-low-energy electron diffraction experiment supported by first-principles calculations based on a Bloch waves treatment of multiple scattering. The experimental unoccupied states of TiTe2 feature dramatic non-free-electron effects such as multiband composition and non-parabolic dispersions. The valence band layer-perpendicular dispersions are then determined from a photoemission experiment consistently interpreted on the basis of the experimental final states to achieve control over the 3-dimensional wavevector. The experimental results demonstrate the absence of the Te 4pz* Fermi surface pocket at the Gamma point and significant self-energy renormalization of the valence band dispersions. Photoemission calculations based on a novel Bloch waves formalism within the one-step theory reveal limitations of understanding photoemission from layered materials such as TiTe2 in terms of direct transitions.
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We present an investigation on electronic structure of 1T-TiTe2 material via high-resolution angle-resolved photoemission spectroscopy (ARPES), utilizing tunable photon energy excitations. The typical semimetal-like electronic structure is observed and examined, where multiple hole pockets related to Te 5p bands and one electron pockets related to Ti 3d band are populated. The obtained results reveals i) a pronounced three-dimensional (3D) electronic structure of 1T-TiTe2 with typical semi-metallic features, for both the Ti 3d and the Te 5p states; ii) multiple Fermi surface (FS) sheets and complex band structure; and iii) an obvious kink in dispersion at an energy of about 18 meV below the Fermi energy, the first experimental observation of a kink structure in 1T-TiTe2, which may originate from electron-phonon coupling. These important and significant findings can help us to gain an in-depth understanding of the 3D electronic structure of semimetallic 1T- TiTe2.
We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the {Gamma}-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical meanfield theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds.
A novel Bloch-waves based one-step theory of photoemission is developed within the augmented plane wave formalism. Implications of multi-Bloch-wave structure of photoelectron final states for band mapping are established. Interference between Bloch components of initial and final states leads to prominent spectral features with characteristic frequency dispersion experimentally observed in VSe_2 and TiTe_2. Interference effects together with a non-free-electron nature of final states strongly limit the applicability of the common direct transitions band mapping approach, making the tool of one-step analysis indispensable.
We have performed angle-resolved photoemission spectroscopy (ARPES) of LaSb and CeSb, a candidate of topological insulator. Using soft-x-ray photons, we have accurately determined the three-dimensional bulk band structure and revealed that the band inversion at the Brillouin-zone corner - a prerequisite for realizing topological-insulator phase - is absent in both LaSb and CeSb. Moreover, unlike the ARPES data obtained with soft-x-ray photons, those with vacuum ultraviolet (VUV) photons were found to suffer significant $k_z$ broadening. These results suggest that LaSb and CeSb are topologically trivial semimetals, and unusual Dirac-cone-like states observed with VUV photons are not of the topological origin.
The compound UTe2 has recently been shown to realize spin triplet superconductivity from a non-magnetic normal state. This has sparked intense research activity, including theoretical analyses that suggest the superconducting order parameter to be topologically nontrivial. However, the underlying electronic band structure is a critical factor for these analyses, and remains poorly understood. Here, we present high resolution angle resolved photoemission (ARPES) measurements covering multiple planes in the 3D Brillouin zone of UTe2, revealing distinct Fermi-level features from two orthogonal quasi-one dimensional light electron bands and one heavy band. The electronic symmetries are evaluated in comparison with numerical simulations, and the resulting picture is discussed as a platform for unconventional many-body order.
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