| 1. |
- Bokai, Kirill A., et al.
(författare)
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Visualization of graphene grain boundaries through oxygen intercalation
- 2021
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 565
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Tidskriftsartikel (refereegranskat)abstract
- Efficient control over the grain boundaries (GBs) is a vital aspect in optimizing the graphene growth conditions. A number of methods for visualization of GBs were developed for graphene grown on weakly interacting surfaces. Here, we utilize oxygen intercalation to reveal GBs and study their morphology for graphene strongly bound to the cobalt surface. We demonstrate that upon the intercalation of oxygen, GBs in polycrystalline graphene become easily detectable due to graphene cracking and selective oxidation of the substrate, thus giving a direct insight into the graphene micro- and nanostructure by means of different electron microscopy methods, including scanning electron microscopy, photoemission microscopy and low-energy electron microscopy.
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| 2. |
- Tarasov, Artem V., et al.
(författare)
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Structural instability at the In-terminated surface of the heavy-fermion superconductor CeIrIn5
- 2022
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Ingår i: Surfaces and Interfaces. - : Elsevier BV. - 2468-0230. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Driven by reconstruction and relaxation, by the appearance of surface electron states and resonances, the surface properties and related temperature scales of strongly correlated f-materials may differ dramatically from those in the bulk. Applying low energy electron and photoelectron diffraction techniques, momentum-resolved photoelectron spectroscopy and ab initio calculations, we demonstrate that the In-terminated surface of the heavyfermion superconductor CeIrIn5 experiences a reconstruction with a (root 2v x root 2)R45 degrees ordered structure. The latter appears due to the displacement of In atoms with respect to the Ir sublattice. We show that the electronic structure and related properties of the reconstructed In surface differ remarkably from the unreconstructed case. Namely, the predicted surface states with Rashba-type spin splitting do not appear. Our results suggest surface instabilities in similar quasi-two-dimensional strongly correlated f-materials, for which surface reconstructions can be unveiled by means of diffraction techniques.
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| 3. |
- Eremeev, S. V., et al.
(författare)
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Insight into the electronic structure of the centrosymmetric skyrmion magnet GdRu 2 Si 2
- 2023
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Ingår i: Nanoscale Advances. - 2516-0230. ; 5:23, s. 6678-6687
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Tidskriftsartikel (refereegranskat)abstract
- The discovery of a square magnetic-skyrmion lattice in GdRu2Si2, with the smallest so far found skyrmion size and without a geometrically frustrated lattice, has attracted significant attention. In this work, we present a comprehensive study of surface and bulk electronic structures of GdRu2Si2 by utilizing momentum-resolved photoemission (ARPES) measurements and first-principles calculations. We show how the electronic structure evolves during the antiferromagnetic transition when a peculiar helical order of 4f magnetic moments within the Gd layers sets in. A nice agreement of the ARPES-derived electronic structure with the calculated one has allowed us to characterize the features of the Fermi surface (FS), unveil the nested region along kz at the corner of the 3D FS, and reveal their orbital compositions. Our findings suggest that the Ruderman-Kittel-Kasuya-Yosida interaction plays a decisive role in stabilizing the spiral-like order of Gd 4f moments responsible for the skyrmion physics in GdRu2Si2. Our results provide a deeper understanding of electronic and magnetic properties of this material, which is crucial for predicting and developing novel skyrmion-based systems.
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| 4. |
- Mende, Max, et al.
(författare)
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Strong Rashba Effect and Different f−d Hybridization Phenomena at the Surface of the Heavy-Fermion Superconductor CeIrIn 5
- 2022
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X .- 2199-160X. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- New temperature scales and remarkable differences from bulk properties have increasingly placed the surfaces of strongly correlated f materials into the focus of research activities. Applying first-principles calculations and angle-resolved photoelectron spectroscopy measurements, a strong Rashba effect and spin-split surface states at the CeIn surface of the heavy-fermion superconductor CeIrIn5 are revealed. The unveiled 4f-derived electron landscape is remarkably distinct for surface and bulk Ce implying the existence of novel temperature scales near the surface region in this material. These results show that ab initio calculations can reliably predict the unusual electronic and spin structure of surfaces of strongly correlated 4f systems where Rashba spin-orbit-coupling phenomena emerge. It is suggested that the structural blocks of such materials can be combined with magnetically active layers for engineering of novel nanostructural objects with appropriate substrates where the diversity of f-driven properties can be applied for the development of novel functionalities.
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| 5. |
- Mende, Max, et al.
(författare)
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Strong Rashba Effect and Different f−d Hybridization Phenomena at the Surface of the Heavy-Fermion Superconductor CeIrIn5
- 2022
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X. ; 8:3
-
Tidskriftsartikel (refereegranskat)abstract
- New temperature scales and remarkable differences from bulk properties have increasingly placed the surfaces of strongly correlated f materials into the focus of research activities. Applying first-principles calculations and angle-resolved photoelectron spectroscopy measurements, a strong Rashba effect and spin-split surface states at the CeIn surface of the heavy-fermion superconductor CeIrIn5 are revealed. The unveiled 4f-derived electron landscape is remarkably distinct for surface and bulk Ce implying the existence of novel temperature scales near the surface region in this material. These results show that ab initio calculations can reliably predict the unusual electronic and spin structure of surfaces of strongly correlated 4f systems where Rashba spin-orbit-coupling phenomena emerge. It is suggested that the structural blocks of such materials can be combined with magnetically active layers for engineering of novel nanostructural objects with appropriate substrates where the diversity of f-driven properties can be applied for the development of novel functionalities.
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| 6. |
- Poelchen, Georg, et al.
(författare)
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Interlayer Coupling of a Two-Dimensional Kondo Lattice with a Ferromagnetic Surface in the Antiferromagnet CeCo2P2
- 2022
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 16:3, s. 3573-3581
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Tidskriftsartikel (refereegranskat)abstract
- The f-driven temperature scales at the surfaces of strongly correlated materials have increasingly come into the focus of research efforts. Here, we unveil the emergence of a two-dimensional Ce Kondo lattice, which couples ferromagnetically to the ordered Co lattice below the P-terminated surface of the antiferromagnet CeCo2P2. In its bulk, Ce is passive and behaves tetravalently. However, because of symmetry breaking and an effective magnetic field caused by an uncompensated ferromagnetic Co layer, the Ce 4f states become partially occupied and spin-polarized near the surface. The momentum-resolved photoemission measurements indicate a strong admixture of the Ce 4f states to the itinerant bands near the Fermi level including surface states that are split by exchange interaction with Co. The temperature-dependent measurements reveal strong changes of the 4f intensity at the Fermi level in accordance with the Kondo scenario. Our findings show how rich and diverse the f-driven properties can be at the surface of materials without f-physics in the bulk.
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| 7. |
- Poelchen, Georg, et al.
(författare)
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Unexpected differences between surface and bulk spectroscopic and implied Kondo properties of heavy fermion CeRh2Si2
- 2020
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Ingår i: npj Quantum Materials. - : Springer Science and Business Media LLC. - 2397-4648. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- Ultra-violet angle-resolved photoemission spectroscopy (UV-ARPES) was used to explore the temperature dependence of the Ce-4f spectral responses for surface and bulk in the antiferromagnetic Kondo lattice CeRh2Si2. Spectra were taken from Ce- and Si-terminated surfaces in a wide temperature range, and reveal characteristic 4f patterns for weakly (surface) and strongly (bulk) hybridized Ce, respectively. The temperature dependence of the Fermi level peak differs strongly for both cases implying that the effective Kondo temperature at the surface and bulk can be rather distinct. The greatly reduced crystal–electric-field (CEF) splitting at the surface gives reason to believe that the surface may exhibit a larger effective Kondo temperature because of a higher local-moment effective degeneracy. Further, the hybridization processes could strongly affect the 4f peak intensity at the Fermi level. We derived the k-resolved dispersion of the Kondo peak which is also found to be distinct due to different sets of itinerant bands to which the 4f states of surface and bulk Ce are coupled. Overall our study brings into reach the ultimate goal of quantitatively testing many-body theories that link spectroscopy and transport properties, for both the bulk and the surface, separately. It also allows for a direct insight into the broader problem of Kondo lattices with two different local-moment sublattices, providing some understanding of why the cross-talking between the two Kondo effects is weak.
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| 8. |
- Tarasov, Artem V., et al.
(författare)
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Crystal electric field and properties of 4f magnetic moments at the surface of the rare-earth compound TbRh2Si2
- 2022
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Ingår i: Physical Review B. - 2469-9950. ; 106:15
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Tidskriftsartikel (refereegranskat)abstract
- The crystal electric field (CEF) plays an essential role in defining the magnetic properties of 4f materials. It forces the charge density of 4f electrons and the related magnetic moment to be oriented along a certain direction in the crystal. The CEF and related magnetic properties were widely studied in the past with focus on bulk of 4f materials, while their surfaces have not received much attention. By the example of the antiferromagnetic material TbRh2Si2 and using first-principles calculations and classical 4f angle-resolved photoemission (PE) measurements, we show how the CEF and related magnetic properties, linked with the orientation of 4f moments, are modified at the surface region. Precisely, we studied the CEF characteristics in individual Tb layers for Tb- and Si-terminated surfaces of TbRh2Si2. We show how strongly the CEF changes near the surface and how dramatically it influences the orientation of the 4f moments relative to the bulk. The instructive message of our study is that a rather valuable information about the CEF-related phenomena can be derived from the temperature dependence of 4f PE spectra. The presented methodology including the theoretical approach can be further applied to many other layered and quasi-2D rare-earth-based materials for unveiling their surface magnetic properties.
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