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Tantalum ditelluride (TaTe_{2}) belongs to the family of layered transition metal dichalcogenides but exhibits a unique structural phase transition at around 170 K that accompanies the rearrangement of the Ta atomic network from a “ribbon chain” to a “butterfly-like” pattern. While multiple mechanisms including Fermi surface nesting and chemical bonding instabilities have been intensively discussed, the origin of this transition remains elusive. Here we investigate the electronic structure of single-crystalline TaTe_{2} with a particular focus on its modifications through the phase transition, by employing core-level and angle-resolved photoemission spectroscopy combined with first-principles calculations. Temperature-dependent core-level spectroscopy demonstrates a splitting of the Ta 4f core-level spectra through the phase transition indicative of the Ta-dominated electronic state reconstruction. Low-energy electronic state measurements further reveal an unusual kink-like band reconstruction occurring at the Brillouin zone boundary, which cannot be explained by Fermi surface nesting or band-folding effects. On the basis of the orbital-projected band calculations, this band reconstruction is mainly attributed to the modifications of specific Ta 5d states, namely, the d_{XY} orbitals (the ones elongating along the ribbon chains) at the center Ta sites of the ribbon chains. The present results highlight the strong orbital-dependent electronic state reconstruction through the phase transition in this system and provide fundamental insights towards understanding complex electron-lattice-bond coupled phenomena.

In intercalated transition metal dichalcogenides (I-TMDCs), transition metal intercalation introduces magnetic phases which in some cases induce topological band crossing. However, evidence of the topological properties remains elusive in such materials. Here, we employ angle-resolved photoemission spectroscopy to reveal the band structure of epitaxially grown ferromagnetic Cr_{1/3}NbSe_{2}. Experimental evidence of the Weyl crossing shows Cr_{1/3}NbSe_{2} to be a topological ferromagnet. This Letter highlights I-TMDCs as a platform towards the interplay of magnetic and topological physics in low-dimensional systems.

When a crystal becomes thin to the atomic level, peculiar phenomena discretely depending on its layer numbers (n) start to appear. Here, we investigate the electronic band dispersions of multilayer WTe_{2} (2–5 layers), by performing laser-based microfocused angle-resolved photoelectron spectroscopy on exfoliated flakes sorted by n. We observe that the holelike valence bands start to cross the Fermi level when the number of layers is increased from 2- to 3 layers, which should be related to the insulator-semimetal transition, as well as the 30–70-meV spin splitting of valence bands manifesting in even n as a signature of stronger structural asymmetry. Our result fully demonstrates the possibility of the large energy-scale band and spin manipulation through the finite-n stacking procedure.

A pair-breaking mechanism of a superconductor under magnetic fields, namely, the origin of the upper critical field H_{c2}, can be categorized into the orbital effect and the paramagnetic effect, which have been separately discussed so far because the physical pictures are totally different. Here we propose a model that unifies these two origins into one formalism with a generalized physical picture. The obtained formula well describes the experimental results on the angle dependence of H_{c2} in a recently developed noncentrosymmetric superconductor, two-dimensional (2D) NbSe_{2}, providing essential information on the spin states of Cooper pairs in 2D NbSe_{2}. The proposed model is widely applicable to all superconductors, offering a powerful approach for comprehensive understanding of the origin of H_{c2}.