arXiv subjects

Karl-Heinz Ernst

Publications and source records attributed to Karl-Heinz Ernst.

4 recordsLinked to original sources

arXiv2026

Adsorption-induced surface magnetism

We report the emergence of adsorption-induced magnetism from heterohelicene molecules on a non-magnetic Cu(100) surface. Spin-polarized low-energy electron microscopy (SP-LEEM) measurements reveal spin-dependent electron reflectivity for enantiopure 7,12,17-trioxa[11]helicene (TO[11]H) monolayers, indicating the formation of a spin-polarized state localized in the topmost copper layer. Control experiments on clean Cu(100) and TO[11]H on highly oriented pyrolytic graphite show no such effect, excluding artifacts and chirality-induced spin selectivity as origins. Spin-polarized density functional theory calculations with hybrid functionals attribute the magnetism to strong chemisorption, which induces hybridization between the molecular HOMO and copper s- and d-states, driving asymmetric spin-polarized charge redistribution at the interface. An extended Newns-Anderson-Grimley model incorporating on-site Coulomb repulsion in Cu d-orbitals reproduces the emergence of interfacial spin polarization above a threshold interaction strength, highlighting the key roles of hybridization parameters and Coulomb correlation. These findings reveal a mechanism for inducing magnetism at molecule-metal interfaces without inherently magnetic components, offering avenues for engineering spin-polarized states in organic-inorganic hybrid systems.

cond-mat.mtrl-sci↗

arXiv2024

Two-dimensional metalorganic ferromagnets

Driven by applications in information technology, the search for new materials with stable, long-range magnetic ordering continues. Metalorganic magnets, involving the coordination of metal atoms with specific organic ligands, are a focus of intense research. These magnets offer customizable properties through synthetic adjustments to ligands or coordination chemistry. Here the synthesis, structural characterization, and magnetic properties of the 2D cyanocarbon magnet NiTCNE is reported. 2D-crystalline domains of this single-layered metalorganic network reach sizes exceeding 30 nanometers through co-deposition of the ligand TCNE (tetracyanoethylene) and Ni atoms on an Au(111) surface under ultrahigh vacuum conditions. Non-contact atomic force microscopy visualizes the structure with atomic resolution. X-ray magnetic circular dichroism establishes the 2D NiTCNE as a ferromagnet, with a very high magnetic remanence, a coercive field of around 1 tesla and a Curie temperature between 10 and 20 kelvin. As metalorganic chemistry opens a large variety of routes of synthesis, we anticipate that this materials research paves the way to new magnetic nanomaterials for spintronics applications.

cond-mat.mtrl-sci↗

arXiv2023

Enantioselective adsorption on magnetic surfaces

From the beginning of molecular theory, the interplay of chirality and magnetism has intrigued scientists. There is still the question if enantiospecific adsorption of chiral molecules occurs on magnetic surfaces. Enantiomer discrimination was conjectured to arise from chirality-induced spin separation within the molecules and exchange interaction with the substrate's magnetization. Here we show that single helical aromatic hydrocarbons undergo enantioselective adsorption on ferromagnetic cobalt surfaces. Spin and chirality sensitive scanning tunneling microscopy reveals that molecules of opposite handedness prefer adsorption onto cobalt islands with opposite out-of-plane magnetization. As mobility ceases in the final chemisorbed state, it is concluded that enantioselection must occur in a physisorbed transient precursor state. State-of-the-art spin-resolved ab initio simulations support this scenario by refuting enantio-dependent chemisorption energies. These findings demonstrate that van der Waals interaction should also include spin-fluctuations which are crucial for molecular magnetochiral processes.

cond-mat.mtrl-sci↗

arXiv2023

Spin-Selective Electron Transport Through Single Chiral Molecules

The interplay between chirality and magnetism has been a source of fascination among scientists for over a century. In recent years, chirality-induced spin selectivity (CISS) has attracted renewed interest. It has been observed that electron transport through layers of homochiral molecules leads to a significant spin polarization of several tens of percent. Despite the abundant experimental evidence gathered through mesoscopic transport measurements, the exact mechanism behind CISS remains elusive. In this study, we report spin-selective electron transport through single helical aromatic hydrocarbons that were sublimed in vacuo onto ferromagnetic cobalt surfaces and examined with spin-polarized scanning tunneling microscopy (SP-STM) at a temperature of 5 K. Direct comparison of two enantiomers under otherwise identical conditions revealed magnetochiral conductance asymmetries of up to 50% when either the molecular handedness was exchanged or the magnetization direction of the STM tip or Co substrate was reversed. Importantly, our results rule out electron-phonon coupling and ensemble effects as primary mechanisms responsible for CISS.

cond-mat.mes-hall↗