Spin-orbit interaction and structure inversion asymmetry in combination with magnetic ordering is a promising route to novel materials with highly mobile spin-polarized carriers at the surface. ...Spin-resolved measurements of the photoemission current from the Si-terminated surface of the antiferromagnet TbRh2Si2 and their analysis within an ab initio one-step theory unveil an unusual triple winding of the electron spin along the fourfold-symmetric constant energy contours of the surface states. A two-band k ⋅ p model is presented that yields the triple winding as a cubic Rashba effect. The curious in-plane spin-momentum locking is remarkably robust and remains intact across a paramagnetic-antiferromagnetic transition in spite of spin-orbit interaction on Rh atoms being considerably weaker than the out-of-plane exchange field due to the Tb 4 f moments.
Abstract
Collective spin excitations in magnetically ordered crystals, called magnons or spin waves, can serve as carriers in novel spintronic devices with ultralow energy consumption. The generation ...of well-detectable spin flows requires long lifetimes of high-frequency magnons. In general, the lifetime of spin waves in a metal is substantially reduced due to a strong coupling of magnons to the Stoner continuum. This makes metals unattractive for use as components for magnonic devices. Here, we present the metallic antiferromagnet CeCo
2
P
2
, which exhibits long-living magnons even in the terahertz (THz) regime. For CeCo
2
P
2
, our first-principle calculations predict a suppression of low-energy spin-flip Stoner excitations, which is verified by resonant inelastic X-ray scattering measurements. By comparison to the isostructural compound LaCo
2
P
2
, we show how small structural changes can dramatically alter the electronic structure around the Fermi level leading to the classical picture of the strongly damped magnons intrinsic to metallic systems. Our results not only demonstrate that long-lived magnons in the THz regime can exist in bulk metallic systems, but they also open a path for an efficient search for metallic magnetic systems in which undamped THz magnons can be excited.
The orientation of the 4f moments offers an additional degree of freedom for engineering the spin-related properties in spintronic nanostructures of lanthanides. Yet, precise monitoring of the ...direction of magnetic moments remains a challenge. Here, on the example of the antiferromagnets HoRh2Si2 and DyRh2Si2, we investigate the temperature-dependent canting of the 4f moments near the surface. We demonstrate that this canting can be understood in the framework of crystal electric field theory and the exchange magnetic interaction. Using photoelectron spectroscopy, we disclose subtle but certain temperature-dependent changes in the line shape of the 4f multiplet. These changes are directly linked to the canting of the 4f moments, which is different for the individual lanthanide layers near the surface. Our results illustrate the opportunity to monitor the orientation of the 4f-moments with high precision, which is essential for development of novel lanthanide-based nanostructures, interfaces, supramolecular complexes, and single-molecule magnets for various applications.
The adsorption and dissociation of molecular oxygen on the surface of N-graphene/Au/Ni(111) epitaxial system with high crystalline quality of N-graphene have been investigated. The system is formed ...in such a way that nitrogen impurities in it are exclusively represented by graphitic and pyridinic configurations in equal concentrations. Using X-ray photoelectron spectroscopy and density functional theory calculations, the relationship between the chemical shift of the N 1
s
core level caused by the adsorption of molecular oxygen and the atomic position of individual oxygen atoms after molecular dissociation has been established.
Discovered in 1962, the divalent ferromagnetic semiconductor EuS (T C = 16.5 K, E g = 1.65 eV) has remained constantly relevant to the engineering of novel magnetically active interfaces, ...heterostructures, and multilayer sequences and to combination with topological materials. Because detailed information on the electronic structure of EuS and, in particular, its evolution across T C is not well-represented in the literature but is essential for the development of new functional systems, the present work aims at filling this gap. Our angle-resolved photoemission measurements complemented with first-principles calculations demonstrate how the electronic structure of EuS evolves across a paramagnetic–ferromagnetic transition. Our results emphasize the importance of the strong Eu 4f–S 3p mixing for exchange-magnetic splittings of the sulfur-derived bands as well as coupling between f and d orbitals of neighboring Eu atoms to derive the value of T C accurately. The 4f–3p mixing facilitates the coupling between 4f and 5d orbitals of neighboring Eu atoms, which mainly governs the exchange interaction in EuS.
The full exploration of the potential, which graphene offers to nanoelectronics requires its integration into semiconductor technology. So far the real-world applications are limited by the ability ...to concomitantly achieve large single-crystalline domains on dielectrics and semiconductors and to tailor the interfaces between them. Here we show a new direct bottom-up method for the fabrication of high-quality atomically precise interfaces between 2D materials, like graphene and hexagonal boron nitride (hBN), and classical semiconductor via Ge intercalation. Using angle-resolved photoemission spectroscopy and complementary DFT modelling we observed for the first time that epitaxially grown graphene with the Ge monolayer underneath demonstrates Dirac Fermions unaffected by the substrate as well as an unperturbed electronic band structure of hBN. This approach provides the intrinsic relativistic 2D electron gas towards integration in semiconductor technology. Hence, these new interfaces are a promising path for the integration of graphene and hBN into state-of-the-art semiconductor technology.
The structural, chemical, and electronic properties of epitaxial graphene films grown by thermal decomposition of the Si-face of a semi-insulating 6
H
-SiC substrate in an argon environment are ...studied by Raman spectroscopy, atomic-force microscopy, the low-energy electron diffraction method, X-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy and X-ray absorption spectroscopy at the carbon
K
edge. It is shown that the results of a systematic integrated study make it possible to optimize the growth parameters and develop a reliable technology for the growth of high-quality single-layer graphene films with a small fraction of bilayer graphene inclusions.
The emergence of ferromagnetism in Rashba systems, where the evolving exchange interaction enters into competition with spin-orbit coupling, leads to a nontrivial spin-polarized electronic landscape ...with an intricate momentum-dependent spin structure, which is challenging to unveil. Here, we show a way to disentangle the contributions from the effective spin-orbit and exchange fields and thus to gain knowledge of the spin structure in ferromagnetic Rashba materials, which is required for spintronic applications. Our approach is based exclusively on spin-integrated photoemission measurements combined with a two-band modeling. As an example, we consider the mixed-valent material EuIr2Si2 which, while being nonmagnetic in the bulk, reveals strong ferromagnetism at the iridium-silicide surface where both spin-orbit and exchange magnetic interactions coexist. The combined effect of these interactions causes a complex band dispersion of the surface state which can be observed in photoemission experiments. Our method allows us to comprehensively unravel the surface-state spin structure driven by spin-orbit coupling at the ferromagnetic surface. This approach opens up opportunities to characterize the spin structure of ferromagnetic Rashba materials, especially where dedicated spin-resolved measurements remain challenging.
We investigate the N = 9 atoms wide armchair‐type graphene nanoribbons (9‐AGNRs) by performing a comprehensive spectroscopic and microscopic characterization of this novel material. In particular, we ...use X‐ray photoelectron, near edge X‐ray absorption fine structure, scanning tunneling, polarized Raman and angle‐resolved photoemission (ARPES) spectroscopies. The ARPES measurements are aided by calculations of the photoemission matrix elements which yield the position in k space having the strongest photoemission cross section. Comparison with well‐studied narrow N = 7 AGNRs shows that the effective electron mass in 9‐AGNRs is reduced by two times and the valence band maximum is shifted to lower binding energy by ∼0.6 eV. In polarized Raman measurements of the aligned 9‐AGNR, we reveal anisotropic signal depending upon the phonon symmetry. Our results indicate the 9‐AGNRs are a novel 1D semiconductor with a high potential in nanoelectronic applications.
Novel narrow‐bandgap graphene nanoribbons with armchair edges and a width of 9 atoms are studied by a multi‐technique approach. The investigation of core‐level and unoccupied states is performed by X‐ray photoelectron spectroscopy and near edge X‐ray absorption. These experiments are complemented by band structure measurements using angle‐resolved photoemission. Finally, the first experimental data on the polarization dependence of the Raman modes of graphene nanoribbons areshown.
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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