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Schwier, Eike F.

Publications and source records attributed to Schwier, Eike F..

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Emergent flat band electronic structure in a VSe 2 /Bi 2 Se 3 heterostructure

Flat band electronic states are proposed to be a fundamental tool to achieve various quantum states of matter at higher temperatures due to the enhanced electronic correlations. However, materials with such peculiar electronic states are rare and often rely on subtle properties of the band structures. Here, by using angle-resolved photoemission spectroscopy, we show the emergent flat band in a VSe 2 / Bi 2 Se 3 heterostructure. Our photoemission study demonstrates that the flat band covers the entire Brillouin zone and exhibits 2D nature with a complex circular dichroism. In addition, the Dirac cone of Bi 2 Se 3 is not reshaped by the flat band even though they overlap in proximity of the Dirac point. These features make this flat band distinguishable from the ones previously found. Thereby, the observation of a flat band in the VSe 2 / Bi 2 Se 3 heterostructure opens a promising pathway to realize strongly correlated quantum effects in topological materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Electronic structure of ferromagnetic heavy fermion, YbPdSi, YbPdGe, and YbPtGe studied by photoelectron spectroscopy, x-ray emission spectroscopy, and DFT + DMFT calculations

Here, the electronic structures of ferromagnetic heavy fermion Yb compounds of YbPdSi, YbPdGe, and YbPtGe are studied by photoelectron spectroscopy around the Yb 4d–4f resonance, resonant x-ray emission spectroscopy at the Yb L 3 absorption edge, and density functional theory combined with dynamical mean field theory calculations. These compounds all have a temperature-independent intermediate Yb valence with large ${\rm Yb}^{3+}$ and small ${\rm Yb}^{2+}$ components. The magnitude of the Yb valence is evaluated to be YbPtGe $<$ YbPdGe $\lesssim $ YbPdSi, suggesting that YbPtGe is the closest to the quantum critical point among the three Yb compounds. Our results support the scenario of the coexistence of heavy fermion behavior and ferromagnetic ordering which is described by a magnetically-ordered Kondo lattice where the magnitude of the Kondo effect and the RKKY interaction are comparable.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2017

Adsorbate doping of MoS 2 and WSe 2 : the influence of Na and Co

Here, we have investigated the influence of metal adsorbates (sodium and cobalt) on the occupied and unoccupied electronic structure of MoS 2 (0 0 0 1) and WSe 2 (0 0 0 1), through a combination of both photoemission and inverse photoemission. The electronic structure is rigidly shifted in both the WSe 2 and MoS 2 systems, with either Na or Co adsorption, generally as predicted by accompanying density functional theory based calculations. Na adsorption is found to behave as an electron donor (n-type) in MoS 2 , while Co adsorption acts as an electron acceptor (p-type) in WSe 2 . The n-type transition metal dichalcogenide (MoS 2 ) is easily doped more n-type with Na deposition while the p-type transition metal dichalcogenide (WSe 2 ) is easily doped more p-type with Co deposition. The binding energy shifts have some correlation with the work function differences between the metallic adlayer and the transition metal dichalcogenide substrate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Covalent versus localized nature of 4 f electrons in ceria: Resonant angle-resolved photoemission spectroscopy and density functional theory

We have conducted resonant angle-resolved photoemission spectroscopy of well-defined CeO 2 (111) and c-Ce 2 O 3 (111) model surfaces, revealing distinct f contributions in the valence band of the two compounds. In conjunction with density functional theory calculations, we show that the f contribution in CeO 2 is of a covalent nature, arising from hybridization with the O2p bands. In contrast, c-Ce 2 O 3 exhibits an almost nondispersive f state at 1.3 eV, which is indicative of almost negligible c-f hybridization.

Duchoň, Tomáš↗