A typical f -electron Kondo lattice system Ce exhibits the well-known isostructural transition, the so-called γ-α transition, accompanied by an enormous volume collapse. Most interestingly, we have discovered that a topological-phase transition also takes place in elemental Ce, concurrently with the γ-α transition. Based on the dynamical mean-field theory approach combined with density functional theory, we have unravelled that the non-trivial topology in α-Ce is driven by the f -d band inversion, which arises from the formation of coherent 4f band around the Fermi level. We captured the formation of the 4f quasi-particle band that is responsible for the Lifshitz transition and the non-trivial Z2 topology establishment across the phase boundary. This discovery provides a concept of "topology switch" for topological Kondo systems. The "on" and "off" switching knob in Ce is versatile in a sense that it is controlled by available pressure (∼ 1 GPa) at room temperature. arXiv:1906.06823v1 [cond-mat.str-el]
The electronic structure of a Möbius Kondo insulator (MKI) candidate of CeRhSb has been investigated by employing angle-resolved photoemission spectroscopy (ARPES), and the density functional theory (DFT) and dynamical mean-field theory (DMFT) band calculations. The Fermi surfaces (FS's) and band structures are successfully measured for three orthogonal crystallographic directions. A sharp Ce 4f peak is observed at the Fermi level (EF), and its temperature (T)evolution agrees with that of the Ce 4f Kondo resonance. The metallic FS's are obtained for all three different (100), (010), and (001) planes. The Ce 4f FS's are described properly by the unfolded DFT calculations considering the reduced Ce-only unit cell. The T-dependence of Ce 4f states as well as the dispersive coherent Ce 4f bands are described well by the DMFT calculations, and reveal the anisotropic c-f hybridization. The photon energy dependence of the Fermi-edge states in CeRhSb reveals the 3D character, consistent with the bulk states dispersing to EF over a larger energy scale rather than the predicted Möbius topological surface states.
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