The quest for quantum ground states beyond the conventional Fermi-liquid paradigm remains a central challenge in many-body physics. The ferromagnetic Kondo effect represents a particularly intriguing case: an exotic variant of the Kondo effect in which an asymptotically free spin gives rise to singular Fermi-liquid behavior. Despite its theoretical importance, this regime has long eluded experimental observation owing to its subtle spectroscopic signatures, vanishingly small energy scales, and strict symmetry constraints in conventional nanostructures. Here, we demonstrate the coexistence of the ferromagnetic and overscreened Kondo effects within a single molecular spin systemx2014a triangulene dimer comprising spin-1 and spin-1/2 units adsorbed on a metal surface. Low-temperature scanning tunneling spectroscopy reveals characteristic signatures of singular Fermi-liquid behavior, which are fully supported by many-body calculations. The unique molecular design provides intrinsic control over spin configuration and coupling asymmetry, allowing distinct many-body regimes to be accessed within the same platform. Our results establish a robust strategy for realizing non-Fermi-liquid physics at the atomic scale and demonstrate that ferromagnetic Kondo behavior can not only be observed but also deliberately engineered in molecular systems.

Recent advances in the synthesis of graphene fragments that possess unpaired π-electrons and display high-spin ground states have unlocked possibilities to explore exotic physical phenomena related to magnetism. The high degree of spin-delocalisation makes these non-metal-based systems ideal building blocks for the construction of chains and lattices with strongly correlated magnetic ground states, which is the main requisite for measurement-based quantum computation. In this work, we demonstrate the magnetic bistability of a diradical nanographene that allows direct spin manipulation at the single-molecule level. To this end, we make use of solution-phase synthesis and tip-induced activation on a metallic surface to construct a helical non-Kekulé hydrocarbon spin switch, with a reversible transformation between a magnetic ground state and a non-magnetic one via intramolecular bond formation/breaking. The switching process is monitored by scanning tunnelling spectroscopy measurements, illustrating that this, and related systems, hold potential as spin-switch units for direct manipulation of magnetism and quantum information in entangled spin systems. Recent advances in the synthesis of graphene fragments that possess unpaired π-electrons and display high-spin ground states have unlocked possibilities to explore exotic physical phenomena related to magnetism. Here, the authors demonstrate the magnetic bistability of a diradical nanographene that allows direct spin manipulation at the single-molecule level.

In molecular electronics, the development of molecular wires capable of carrying high electrical current with minimal loss remains a central challenge, despite extensive efforts in both solution-phase and ultrahigh-vacuum synthesis. Graphene nanoribbons (GNRs) with their structural robustness and tunable electronic properties have emerged as promising candidates. In particular, topologically engineered GNRs with atomically precise edge modifications offer new routes for efficient charge transport. Here, we systematically investigate the transport properties of a staggered, edge-extended GNR based on a 7-AGNR backbone, denoted as 7-AGNR-S(1,3), using low-temperature scanning tunneling microscopy liftoff experiments. Under favorable junction conditions, the conductance remains nearly constant during tip retraction over junction lengths exceeding 10 nm, mediated by the low-energy bands arising from the coupled topological zero-energy edge states. Additionally, we developed a detailed model of the liftoff process and simulated charge transport, revealing the roles of delocalized valence band states and showing how local potential variations at the electrode interfaces can modulate molecular-level alignment and conductance. Our findings underscore the importance of interface engineering in the design of high-performance molecular electronic devices.

Achieving long-range ferrimagnetic order in purely organic systems remains a major challenge in molecular magnetism. Here we report the synthesis and characterization of heterospin-coupling motifs, formed by covalently linking spin-1/2 and spin-1 triangular nanographenes. A combined solution-phase and on-surface synthetic strategy yields three distinct compounds, whose structures are elucidated by bond-resolved scanning probe microscopy. Starting from a spin-1/2–spin-1 dimer as the elemental ferrimagnetic unit, we employ inelastic electron tunneling spectroscopy to resolve low-energy magnetic excitations and extract the parameters of the Heisenberg Hamiltonian. Extension to trimeric architectures results in two distinct spin configurations, with compensated (S=0) and uncompensated (S=3/2) ferrimagnetic ground states. The Heisenberg model accurately describes all magnetic transitions, offering direct insight into increasingly complex spin Hamiltonians. These findings establish a molecular platform for designing tunable heterospin systems with robust exchange interactions, opening routes toward multi-level spin encoding in qudit-based quantum technologies.

Heteroatom substitution is a powerful route to tune the chemical and electronic properties of carbon nanomaterials. In particular, replacement of an sp2 hybridized carbon atom in the graphene lattice with a nitrogen atom (denoted as graphitic nitrogen) induces substantial changes in the electronic properties. These include changes in the band structure that can influence electronic transport, and magnetism. A key requirement for applications is both the periodic and precise incorporation of the heteroatoms in extended carbon lattices. Here, we report the on-surface synthesis and characterization of two one dimensional carbon nanostructures, a polymer and a graphene nanoribbon, consisting of periodically incorporated graphitic nitrogen atoms. The on-surface reactions toward formation of the nanostructures were monitored by scanning tunneling microscopy. The bond-resolved chemical structures of the reaction intermediates and products were investigated by atomic force microscopy, which enabled atomic-scale visualization of the graphitic nitrogen sites. The electronic properties of the nanostructures were studied by scanning tunneling spectroscopy and density functional theory calculations. Our analyses revealed the presence of localized nitrogen-centered electronic states. In the gas phase where the nanostructures are in a neutral charge state, these states undergo spin polarization leading to an open-shell ground state. Upon adsorption on Au(111), the nanostructures exhibit electron transfer to the surface, which resulted in a closed-shell ground state. Our results demonstrate a straightforward and generally applicable route to synthesize graphitic nitrogen-substituted carbon nanomaterials with potential applications in spintronics, catalysis and energy storage.

The on-surface synthesis of porphyrin-nanographene (Por-NG) hybrids enables systematic control of π-electron magnetism in organic materials, yet the spin behavior of these systems remains difficult to predict because the porphyrin core perturbs the graphene lattice. We report the fabrication and electronic characterization of ZnPors fused with two and four [3]triangulene units (i.e. ZnPorT2 and ZnPorT4 , respectively) on Au(111). Rapid thermal annealing maximizes the yield of discrete hybrids by suppressing surface diffusion and unwanted lateral fusion. Scanning tunneling microscopy and spectroscopy, supported by theory, show that both ZnPorT2 and ZnPorT4 exhibit diradical character with an antiferromagnetically coupled ground state. The hybrids undergo interfacial charge transfer to the metallic substrate: ZnPorT2 donates one electron, forming open-shell ZnPorT2 • + , while ZnPorT4 donates two electrons, affording closed-shell ZnPorT4 2+ . Despite this charge transfer, the multireference character of the frontier orbitals remains in ZnPorT2 • + . The results establish an efficient route to complex Por-NG hybrids and clarify how molecular design and interfacial charge transfer shape their magnetic properties, an essential step toward functional magnetic nanoarchitectures.

Inferring microscopic Hamiltonians from experimental data is a central challenge in quantum materials and quantum simulation. In low-dimensional spin systems, exchange interactions are often assumed to be spatially uniform, despite structural and environmental inhomogeneities that can locally modify the coupling. Here, we leverage a local, length-independent machine learning methodology to reconstruct spatially modulated exchange interactions directly from inelastic scanning tunneling spectroscopy maps. We demonstrate this approach with nanographene spin chains, identifying both near-uniform and inhomogeneous regimes across the synthesized magnets. The reconstructed models quantitatively reproduce the experimental spectra and recover the correct scaling of the excitation gap with system size. Our results establish a general strategy to bridge local spectroscopic measurements with effective many-body Hamiltonians.

Single molecule chemistry leveraging scanning probe tip-based atom manipulation is used to create cyclic C6, a previously elusive carbon nanoring, shedding new light on the stability, structure and electronic properties of low-dimensional carbon allotropes.

Inelastic electron tunneling spectroscopy (IETS) is a powerful measurement technique often used in scanning tunneling spectroscopy to probe excited states of various nanostructures, e.g., the magnetic properties of complex spin systems. The observed excited states can be of magnetic and vibrational origin, and it is therefore necessary to differentiate between these two excitation mechanisms. Here, we investigate the spin S = 1/2 phenalenyl radical on Au(111). IETS measurements feature inelastic excitations, whereas the spatial distribution of their intensities excludes any spin excitations. Comparison to theoretical simulations proves the vibrational origin of those excitations and allows us to assign the observed features to distinct vibrational modes.

On-surface synthesis enables the fabrication of atomically precise graphene nanoribbons (GNRs) with properties defined by their shape and edge topology. While this bottom-up approach provides unmatched control over electronic and structural characteristics, integrating GNRs into functional electronic devices requires their transfer from noble metal growth surfaces to technologically relevant substrates. However, such transfers often induce structural modifications, potentially degrading or eliminating GNRs' desired functionality - a process that remains poorly understood. In this study, we employ low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) to characterize 9-atom-wide armchair GNRs (9-AGNRs) following polymer-free wet-transfer onto epitaxial graphene (EG) and quasi-freestanding epitaxial graphene (QFEG) substrates. Our results reveal that armchair GNRs maintain their structural integrity post-transfer, while GNRs with extended or modified edge topologies exhibit significant structural changes, including partial disintegration. Additionally, STS measurements reveal differences in the Fermi level alignment between GNRs and the graphene substrates, a key factor in optimizing carrier injection efficiency in electronic transport devices. This study establishes a framework for detecting postprocessing structural modifications in GNRs, which are often hidden in optical ensemble measurements. By addressing the challenges of substrate transfer and providing insights into GNR-substrate interactions, these findings pave the way for the reliable integration of atomically precise GNRs into next-generation nanoelectronic and optoelectronic devices.

Antiferromagnetic Heisenberg chains exhibit two distinct types of excitation spectrum: gapped for integer-spin chains and gapless for half-integer-spin chains. However, in finite-length half-integer-spin chains, quantization induces a gap, requiring precise control over sufficiently long chains to study its evolution. Here we create length-controlled spin-1/2 Heisenberg chains by covalently linking Olympicenes—Olympic-ring-shaped magnetic nanographenes. With large exchange interactions, tunable lengths and negligible magnetic anisotropy, this system is ideal for investigating length-dependent spin excitations, probed via inelastic electron tunnelling spectroscopy. We observe a power-law decay of the lowest excitation energy with length L , following a 1/ L dependence in the large- L regime, consistent with theory. For L = 50, a V-shaped excitation continuum confirms a gapless behaviour in the thermodynamic limit. Additionally, low-bias current maps reveal the standing wave of a single spinon in odd-numbered chains. Our findings provide evidence for the realization of a one-dimensional analogue of a gapless spin liquid within an artificial graphene lattice.

Open-shell nanographenes have attracted significant attention due to their structurally tunable spin ground state. While most characterization has been conducted on weakly interacting substrates such as noble metals, the influence of magnetic surfaces remains largely unexplored. In this study, we investigate how TbAu2, a rare-earth-element-based surface alloy, affects the magnetic properties of phenalenyl (or [2]triangulene (2T)), the smallest spin-1/2 nanographene. Scanning tunneling spectroscopy (STS) measurements reveal a striking contrast: while 2T on Au(111) exhibits a zero-bias Kondo resonance─a hallmark of a spin-1/2 impurity screened by the conduction electrons of the underlying metal─deposition on TbAu2 induces a symmetric splitting of this feature by approximately 20 mV. This opening is large compared to the few meV splitting induced by externally applied magnetic fields. We attribute this splitting to a strong proximity-induced interaction with the ferromagnetic out-of-plane magnetization of TbAu2. Moreover, our combined experimental and many-body model analysis demonstrates that this interaction is spatially modulated, following the periodicity of the TbAu2 surface superstructure. These findings highlight that TbAu2 serves as a viable platform for stabilizing and characterizing the magnetic properties of spin-1/2 nanographenes and for studying the interactions of more complex π-magnetic materials with magnetic substrates.

Chiral graphene nanoribbons offer a versatile playground to control electronic and magnetic prop-erties in a onedimensional graphene nanostructure. Here, we report the on-surface synthesis of (4,1,4) chiral graphene nanoribbons (chGNRs) and characterize their structure, edge states and band gaps using scanning probe techniques and DFT simulations, the latter revealing a critical dependence on the environment of the electronic and magnetic properties of (4,1,4)-chGNRs. While gas phase calculations predict an open-shell ground state, the influence of the metallic substrate upon adsorption modifies the electronic properties as predicted by GW calculations. In this theoretical frame, the experimental band gap of surface-supported (4,1,4)-chGNRs can only be reproduced assuming a closed-shell configuration.

Seventeen-carbon-atom-wide armchair graphene nanoribbons (17-AGNRs) are promising candidates for high-performance electronic devices due to their narrow electronic bandgap. Atomic precision in edge structure and width control is achieved through a bottom-up on-surface synthesis (OSS) approach from tailored molecular precursors in ultra-high vacuum (UHV). This synthetic protocol must be optimized to meet the structural requirements for device integration, with ribbon length being the most critical parameter. Here, we report optimized OSS conditions that produce 17-AGNRs with an average length of approximately 17 nm. This length enhancement is achieved through a gradual temperature ramping during an extended annealing period, combined with a template-like effect driven by monomer assembly at high surface coverage. The resulting 17-AGNRs are comprehensively characterized in UHV using scanning probe techniques and Raman spectroscopy. Raman measurements following substrate transfer enabled the characterization of the length distribution of GNRs on the device substrate and confirmed their stability under ambient conditions and harsh chemical environments, including acid vapors and etchants. The increased length and ambient stability of the 17-AGNRs lead to their reliable integration into device architectures. As a proof of concept, we integrate 17-AGNRs into field-effect transistors (FET) with graphene electrodes and confirm that electronic transport occurs through the GNRs. This work demonstrates the feasibility of integrating narrow-bandgap GNRs into functional devices and contributes to advancing the development of carbon-based nanoelectronics.

Polyacene analogues, consisting of short acene segments separated by nonbenzenoid rings, offer intriguing electronic properties and magnetic interactions. Pentalene-bridged polyacenes (PPs), in particular, hold promise for enhancing the electrical conductivity and potential open-shell ground states. However, PPs have remained elusive in solution chemistry due to poor solubility and limited synthetic protocols. Here, we report the on-surface synthesis of PPs through the annulation between ortho-xylene groups. Scanning tunneling microscopy and atomic force microscopy reveal that the reconstructed Au(110) surface significantly enhances the chemoselectivity of the annulation process. Scanning tunneling spectroscopy combined with density functional theory suggests that PP exhibits a narrow direct band gap, similar to long acenes. This work demonstrates the potential for band structure engineering in polyacene analogues by incorporating nonbenzenoid rings, paving the way to advancements in organic electronics and spintronics.

This study investigates the growth mechanism of graphene nanoribbons (GNRs) on vicinal surfaces and the influence of precursor coverage on the quality and alignment of GNRs on the growth substrate and upon substrate transfer.

Molecular assemblies based on porphyrins (Pors), specifically Por nanotapes (NTs) containing magnetic metal ions, offer a versatile platform to explore magnetic interactions arising from the electronic interplay between -conjugated ligands and transition metal d -orbitals. Using on-surface synthesis under ultra-high vacuum, we synthesized -extended PorNTs of different lengths incorporating magnetic metal ions such as Fe and Co on Au(111). We resolved their atomic structure using scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). Differential conductance ( ) measurements, interpreted by extensive density functional theory calculations and theoretical modeling, reveal two distinct magnetic behaviors for the Fe- and Co-based systems. In FePorNTs, the magnetic interactions are dominated by strong Fe–ligand ferromagnetic coupling and weak antiferromagnetic Fe–Fe coupling. By contrast, CoPorNTs exhibit stronger Co–Co antiferromagnetic exchange and weaker Co–ligand coupling, with Kondo screening evident at the ligand sites. Our findings underscore the profound influence of metal centers, ligands, and substrate interactions on the magnetic and electronic properties of PorNTs, establishing these assemblies as interesting building blocks for low-dimensional magnetism and future spintronic or quantum-material applications.

Graphene nanoribbons (GNRs) with zigzag edges are promising materials for spintronic devices due to tunable bandgaps and spin-polarized edge states. Porphyrins offer complementary benefits such as desirable optoelectronic properties. Here we combine these features in a hybrid system by means of the on-surface synthesis of zigzag-edge GNRs embedded with porphyrins laterally fused along the ribbon backbone. Using scanning probe methods, we show that this design achieves strong electronic coupling between the porphyrin and the GNR. For transition metal porphyrins, pronounced exchange coupling between distant metal centres is mediated by the π-electron system. Such a hybrid d and π electron ribbon system introduces spin–orbit coupling and magnetic anisotropy to carbon nanomaterials, and holds great promise for coherent electrical control of electron spins. Graphene nanoribbons with zigzag edges are key candidates for spintronic applications due to their tunable bandgaps and spin-polarized edge states. Now it has been shown that hybrid ribbons embedded with metalloporphyrins enable strong electronic and magnetic coupling between distant metal centres, positioning such hybrids as promising materials for quantum devices.

Conventional methods to measure the dispersion relations of collective spin excitations involve probing bulk samples with particles such as neutrons, photons or electrons, which carry a well-defined momentum. Open-ended finite-size spin chains, on the contrary, do not have a well-defined momentum due to the lack of translation symmetry, and their spin excitations are measured with an eminently local probe, using inelastic electron tunneling spectroscopy (IETS) with a scanning tunneling microscope (STM). Here we discuss under what conditions STM-IETS spectra can be Fourier-transformed to yield dispersion relations in these systems. We relate the success of this approach to the degree to which spin excitations form standing waves. We show that STM-IETS can reveal the energy dispersion of magnons in ferromagnets and triplons in valence bond crystals, but not that of spinons, the spin excitations in Heisenberg spin-1/2 chains. We compare our theoretical predictions with state-of-the-art measurements on nanographene chains that realize the relevant spin Hamiltonians.

On-surface synthesis enables the fabrication of atomically precise graphene nanoribbons (GNRs) with properties defined by their shape and edge topology. While this bottom-up approach provides unmatched control over electronic and structural characteristics, integrating GNRs into functional electronic devices requires their transfer from noble metal growth surfaces to technologically relevant substrates. However, such transfers often induce structural modifications, potentially degrading or eliminating GNRs' desired functionality - a process that remains poorly understood. In this study, we employ low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) to characterize 9-atom-wide armchair GNRs (9-AGNRs) following polymer-free wet-transfer onto epitaxial graphene (EG) and quasi-freestanding epitaxial graphene (QFEG) substrates. Our results reveal that armchair GNRs maintain their structural integrity post-transfer, while GNRs with extended or modified edge topologies exhibit significant structural changes, including partial disintegration. Additionally, STS measurements reveal differences in the Fermi level alignment between GNRs and the graphene substrates, a key factor in optimizing carrier injection efficiency in electronic transport devices. This study establishes a framework for detecting post-processing structural modifications in GNRs, which are often hidden in optical ensemble measurements. By addressing the challenges of substrate transfer and providing new insights into GNR-substrate interactions, these findings pave the way for the reliable integration of atomically precise GNRs into next-generation nanoelectronic and optoelectronic devices.