Symmetry mediated tunable molecular magnetism on a 2D material

TL;DR

This study demonstrates that the magnetic and electronic states of cobalt phthalocyanine molecules on a 2D superconductor can be tuned by adjusting their relative orientation, revealing symmetry-dependent magnetic phenomena.

Contribution

It introduces a novel approach to controlling molecular magnetism on 2D materials through symmetry alignment, highlighting the role of spin-orbit coupling and non-collinear exchange interactions.

Findings

Molecular charge and spin states change with alignment.

Observation of singlet-triplet transition due to magnetic interactions.

Symmetry-dependent magnetic properties influenced by spin-orbit coupling.

Abstract

The induction of unconventional superconductivity by twisting two layers of graphene a small angle was groundbreaking1, and since then has attracted widespread attention to novel phenomena caused by lattice or angle mismatch between two-dimensional (2D) materials2. While many studies address the influence of angle mismatch between layered 2D materials3-5 , the impact of the absorption alignment on the physical properties of planar molecules on 2D substrates has not been studied in detail. Using scanning probe microscopy (SPM) we show that individual cobalt phthalocyanine (CoPc) molecules adsorbed on the layered superconductor 2H-NbSe2 change drastically their charge and spin state when the symmetry axes of the molecule and the substrate are twisted with respect to each other. The CoPc changes from an effective spin-1/2 as found in gas-phase6 to a molecule with non-magnetic ground-state. On the latter we observe a singlet-triplet transition originating from an antiferromagnetic interaction between the central-ion spin and a distributed magnetic moment on the molecular ligands. Because the Ising superconductor 2H-NbSe2 lacks inversion symmetry and has large spin-orbit coupling7 this intramolecular magnetic exchange has significant non-collinear Dzyaloshinskii-Moriya (DM)8, 9 contribution.