arXiv subjects

Lorenz Meyer

Publications and source records attributed to Lorenz Meyer.

3 recordsLinked to original sources

arXiv2026

Single-enantiomer spin polarisers in superconducting junctions

Chiral matter acting as a spin-selective device in biased electron transport is attracting attention for the quantum-technological design of miniaturized electronics. To date, however, experimental reports on spin selectivity are not conclusive. The magnetoresistance in electron transport measurements observed for chiral materials on ferromagnets upon magnetisation reversal is proposed to result from electrostatic rather than from the sought-after chiral effects. Recent break junction studies even question the spin-dependent electron flow across single chiral molecules. Here, we avoid ferromagnetic electrodes and magnetisation reversal to provide unambiguous experimental evidence for the chirality-induced spin selectivity effect of single enantiomers. Functionalising the superconducting tip of a scanning tunnelling microscope with a manganese atom cluster gives rise to Yu-Shiba-Rusinov resonances that serve as spin-sensitive probes of the tunnelling current in junctions of single heptahelicene molecules adsorbed on a crystalline lead surface. Our key finding is the dependence of the signal strength of these states in spectroscopy of the differential conductance on the handedness of the molecule. The experiments unveil the role of the enantiomers as spin polarisers and the irrelevance of electrostatics in the chosen model system.

cond-mat.mes-hall↗

arXiv2025

Control of Andreev Reflection via a Single-Molecule Orbital

Charge transport across a single-molecule junction fabricated from a normal-metal tip, a phthalocyanine, and a conventional superconductor in a scanning tunneling microscope is explored as a function of the gradually closed vacuum gap. The phthalocyanine (2H-Pc) molecule and its pyrrolichydrogen-abstracted derivative (Pc) exhibit vastly different behavior. Andreev reflection across the 2H-Pc contact exhibits a temporary enhancement that diminishes with increasing conductance. The hybridization of 2H-Pc with the tip at contact formation gives rise to a Kondo-screened molecular magnetic moment. In contrast, the single-Pc junction lacks Andreev reflection in the same conductance range. Spectroscopies and supporting nonequilibrium Green function calculations highlight the importance of a molecular orbital close to the Fermi energy for Andreev reflection.

cond-mat.mes-hall↗

arXiv2023

On-Surface Synthesis and Characterization of a High-Spin Aza-[5]-Triangulene

Triangulenes are open-shell triangular graphene flakes with total spin increasing with their size. In the last years, on-surface-synthesis strategies have permitted fabricating and engineering triangulenes of various sizes and structures with atomic precision. However, direct proof of the increasing total spin with their size remains elusive. In this work, we report the combined in-solution and on-surface synthesis of a large nitrogen-doped triangulene (aza-[5]-triangulene) and the detection of its high spin ground state on a Au(111) surface. Bond-resolved scanning tunneling microscopy images uncovered radical states distributed along the zigzag edges, which were detected as weak zero-bias resonances in scanning tunneling spectra. These spectral features reveal the partial Kondo screening of a high spin state. Through a combination of several simulation tools, we find that the observed distribution of radical states is explained by a quintet ground state (S = 2), instead of the expected quartet state (S = 3/2), confirming the positively charged state of the molecule on the surface. We further provide a qualitative description of the change of (anti)aromaticity introduced by N-substitution, and its role in the charge stabilization on a surface, resulting in a S = 2 aza-[5]-triangulene on Au(111).

cond-mat.mes-hall↗