| 1. |
- 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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| 2. |
- Mende, Max, et al.
(författare)
-
Strong Rashba Effect and Different f−d Hybridization Phenomena at the Surface of the Heavy-Fermion Superconductor CeIrIn5
- 2022
-
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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| 3. |
- Senkovskiy, Boris V., et al.
(författare)
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Semiconductor-to-Metal Transition and Quasiparticle Renormalization in Doped Graphene Nanoribbons
- 2017
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X. ; 3:4
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Tidskriftsartikel (refereegranskat)abstract
- A semiconductor-to-metal transition in N = 7 armchair graphene nanoribbons causes drastic changes in its electron and phonon system. By using angle-resolved photoemission spectroscopy of lithium-doped graphene nanoribbons, a quasiparticle band gap renormalization from 2.4 to 2.1 eV is observed. Reaching high doping levels (0.05 electrons per atom), it is found that the effective mass of the conduction band carriers increases to a value equal to the free electron mass. This giant increase in the effective mass by doping is a means to enhance the density of states at the Fermi level which can have palpable impact on the transport and optical properties. Electron doping also reduces the Raman intensity by one order of magnitude, and results in relatively small (4 cm−1) hardening of the G phonon and softening of the D phonon. This suggests the importance of both lattice expansion and dynamic effects. The present work highlights that doping of a semiconducting 1D system is strikingly different from its 2D or 3D counterparts and introduces doped graphene nanoribbons as a new tunable quantum material with high potential for basic research and applications.
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| 4. |
- Generalov, Alexander, et al.
(författare)
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Spin Orientation of Two-Dimensional Electrons Driven by Temperature-Tunable Competition of Spin-Orbit and Exchange-Magnetic Interactions
- 2017
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 17:2, s. 811-820
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Tidskriftsartikel (refereegranskat)abstract
- Finding ways to create and control the spin-dependent properties of two-dimensional electron states (2DESs) is a major challenge for the elaboration of novel spin-based devices. Spin-orbit and exchange-magnetic interactions (SOI and EMI) are two fundamental mechanisms that enable access to the tunability of spin-dependent properties of carriers. The silicon surface of HoRh2Si2 appears to be a unique model system, where concurrent SOI and EMI can be visualized and controlled by varying the temperature. The beauty and simplicity of this system lie in the 4f moments, which act as a multiple tuning instrument on the 2DESs, as the 4f projections parallel and perpendicular to the surface order at essentially different temperatures. Here we show that the SOI locks the spins of the 2DESs exclusively in the surface plane when the 4f moments are disordered: the Rashba-Bychkov effect. When the temperature is gradually lowered and the system experiences magnetic order, the rising EMI progressively competes with the SOI leading to a fundamental change in the spin-dependent properties of the 2DESs. The spins rotate and reorient toward the out-of-plane Ho 4f moments. Our findings show that the direction of the spins and the spin-splitting of the two-dimensional electrons at the surface can be manipulated in a controlled way by using only one parameter: the temperature.
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| 5. |
- 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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| 6. |
- Liu, Xianjie, et al.
(författare)
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Tunable Interface Properties between Pentacene and Graphene on the SIC Substrate
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 117:8, s. 3969-3975
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Tidskriftsartikel (refereegranskat)abstract
- Understanding energy-level alignment and molecular growth characteristics of an organic semiconductor on the graphene surface is crucial for graphene-related device performance. Here we demonstrate that tunable interface properties and molecular orientation can be achieved by modifying graphene films on a SiC substrate with monolayer copper-hexadecafluorophthalocyanine (F16CuPc) molecules. On clean graphene, pentacene molecules form a tilted configuration even at very low coverage (one or two monolayers) rather than flat-lying as on the graphite surface. Pentacene molecules prefer to grow with a (022) plane parallel to the clean graphene surface. With increasing coverage, X-ray adsorption data indicate there is no obvious change of molecular stacking orientation. The corresponding hole injection barrier is about 0.7 eV. On the modified graphene where thin (one or two monolayers) F16CuPc molecules are flat-lying on graphene, an almost perfect up-standing molecular stacking of pentacene film was formed on the modified surface. A low hole injection barrier of 0.3 eV was observed. Furthermore, the interface of dirty graphene upon pentacene was also discussed.
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