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We demonstrate the reversible control of interactions between a local molecular spin, hosted within an iron phthalocyanine (FePc) molecule, and the conduction electrons of a supporting Au(111) surface. Using the tip of a scanning tunneling microscope, we deliberately and reversibly manipulate the adsorption configuration of the molecule relative to the underlying substrate lattice. Different rotation configurations lead to noticeable changes in the differential conductance measured on the FePc molecules. In one configuration, a Kondo resonance is observed, while in others, spin excitations are revealed. To further explore the impact of the local environment, we designed a series of molecular assemblies in which neighboring molecules surrounding the target molecule are incrementally increased. In this structured approach, we observed a step-by-step transition of the spin excitation state to a Kondo resonance, ultimately resulting in a pure Kondo feature.

Many-body interactions in metal-organic frameworks (MOFs) are fundamental for emergent quantum physics. Unlike their solution counterpart, magnetization at surfaces in low-dimensional analogues is strongly influenced by magnetic anisotropy (MA) induced by the substrate and still not well understood. Here, on-surface coordination chemistry is used to synthesize on Ag(111) and superconducting Pb(111) an iron-based spin chain by using pyrene-4,5,9,10-tetraone (PTO) precursors as ligands. Using low-temperature scanning probe microscopy, their structures and low-energy spin excitations of coordinated Fe atoms are compared with high S = 2 spin-state. Although the chain and coordination centers are identical on both substrates, the long-range spin-spin coupling due to a superexchange through the ligand on Ag is not experimentally observed on Pb(111). This reduction of spin-spin interactions on Pb in tunneling spectra is ascribed to the depletion of electronic states around the Fermi level of the Pb(111) superconductor as compared to silver., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Single metallocene molecules act as sensitive spin detectors when decorating the probe of a scanning tunneling microscope (STM). However, the impact of the atomic-scale electrode details on the molecular spin state has remained elusive to date. Here, a nickelocene (Nc) STM junction is manipulated in an atomwise manner showing clearly the dependence of the spin excitation spectrum on the anchoring of Nc to Cu(111), a Cu monomer, and trimer. Moreover, while the spin state of the same Nc tip is a triplet with tunable spin excitation energies upon contacting the surface, it transitions to a Kondo-screened doublet on a Cu atom. Notably, the nontrivial magnetic exchange interaction of the molecular spin with the electron continuum of the substrate determines the spectral line shape of the spin excitations.

Triangulene nanographenes are open‐shell molecules with predicted high spin state due to the frustration of their conjugated network. Their long‐sought synthesis became recently possible over a metal surface. Here, we present a macrocycle formed by six [3]triangulenes, which was obtained by combining the solution synthesis of a dimethylphenyl‐anthracene cyclic hexamer and the on‐surface cyclodehydrogenation of this precursor over a gold substrate. The resulting triangulene nanostar exhibits a collective spin state generated by the interaction of its 12 unpaired π‐electrons along the conjugated lattice, corresponding to the antiferromagnetic ordering of six S=1 sites (one per triangulene unit). Inelastic electron tunneling spectroscopy resolved three spin excitations connecting the singlet ground state with triplet states. The nanostar behaves close to predictions from the Heisenberg model of an S=1 spin ring, representing a unique system to test collective spin modes in cyclic systems. [ABSTRACT FROM AUTHOR]

Inelastic electron tunneling spectroscopy (IETS) based on scanning tunneling microscopy (STM) opens a new avenue for vibrational spectroscopy at single bond level. Since its birth, STM-IETS has been widely used for chemical identification and investigating the intra- and inter-molecular interactions as well as chemical reactions. In this review, we mainly focus on the new development and application of STM-IETS in the past decade. After introducing the basic theoretical background of IETS, we will discuss the recent advances of STM-IETS as vibrational spectroscopy and microspectroscopy, with emphasis on the ability of probing weak intermolecular interactions. The coupling of inelastic tunneling electrons to other elementary excitations, such as rotation, phonon, spin, plasmon, photon, etc., will be also briefly reviewed. In the end, we present a perspective for the future directions and challenges of STM-IETS. The goal of this review is to demonstrate the versatility of STM-IETS and inspire new applications in interdisciplinary fields.

The adsorbed magnetic molecules with tunable spin states have drawn wide attention for their immense potential in the emerging fields of molecular spintronics and quantum computing. One of the key issues toward their application is the efficient controlling of their spin state. This review briefly summarizes the recent progress in the field of molecular spin state manipulation on surfaces. We focus on the molecular spins originated from the unpaired electrons of which the Kondo effect and spin excitation can be detected by scanning tunneling microscopy and spectroscopy (STM and STS). Studies of the molecular spin-carriers in three categories are overviewed, i.e., the ones solely composed of main group elements, the ones comprising 3d-metals, and the ones comprising 4f-metals. Several frequently used strategies for tuning molecular spin state are exemplified, including chemical reactions, reversible atomic/molecular chemisorption, and STM-tip manipulations. The summary of the successful case studies of molecular spin state manipulation may not only facilitate the fundamental understanding of molecular magnetism and spintronics but also inspire the design of the molecule-based spintronic devices and materials.

The S = 1 / 2 kagome- and triangular-lattice Heisenberg antiferromagnets are investigated using the numerical exact diagonalization and the finite-size scaling analysis. The behaviour of the field derivative at zero magnetization is examined for both systems. The present result indicates that the spin excitation is gapless for each system. [ABSTRACT FROM AUTHOR]

Superconductivity in copper oxides emerges on doping holes or electrons into their Mott-insulating parent compounds. The spin excitations are thought to be the mediating glue for the pairing in superconductivity. Here the momentum and doping dependence of the dynamical spin response in the electron-doped cuprate superconductors is studied based on the kinetic-energy-driven superconducting mechanism. It is shown that the dispersion of the low-energy spin excitations changes strongly upon electron doping; however, the hour-glass-shaped dispersion of the low-energy spin excitations appeared in the hole-doped case is absent on the electron-doped side due to the electron-hole asymmetry. In particular, the commensurate resonance appears in the superconducting state with the resonance energy that correlates with the dome-shaped doping dependence of the superconducting gap. Moreover, the spectral weight and dispersion of the high-energy spin excitations in the superconducting state are comparable with those in the corresponding normal state, indicating that the high-energy spin excitations do not play an important part in the pair formation. [ABSTRACT FROM AUTHOR]

Spin excitation in poly(1,4-bis(2,2,6,6-tetramethyl-4-oxy-piperidyl-1-oxyl)-butadiin) (poly-BIPO), a quasi-one-dimensional organic ferromagnet, was investigated based on the extended Su-Schriffer-Heeger model by considering electron hopping and the spin correlation between the main chain and side radicals. The lattice, charge density, and spin density configurations of the single spin as well as spin domain excited states of the organic ferromagnet poly-BIPO were systematically studied. The side radical spin excitation gives rise to lattice distortion, charge density localization, and a spin density defect on the main chain. A peak induced by spin excitation is predicted to appear in the density of states of the organic ferromagnet poly-BIPO based on calculations for different spin electron states. These results expand knowledge on elementary excitation in organic materials and have significant implications for the design of spintronic devices. [ABSTRACT FROM AUTHOR]

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