Fig. 3: Determining the spin order in diradical nanographene dimers by spin-flip spectroscopy.

a Chemical structure and nc-AFM image (Resonant frequency: 29 KHz, Oscillation amplitude: 160 pm) of a BNG–BNG dimer. b Constant-height current image (Bias voltage: 1 mV) and simulated LDOS map of the dimer in a. c dI/dV spectra (modulation: 0.1 mV, Temperature: 1.1 K) and numerical calculated dI²/dV² spectra taken on the two locations marked in b. Three resonances have been detected, suggesting a ferromagnetic coupled ground state with S = 1. The black dashed line is simulated line shape using a perturbative approach up to third order. d Chemical structure and nc-AFM image (Resonant frequency: 22 KHz, Oscillation amplitude: 140 pm) of a BNG–nBNG hetero-dimer. e Constant-height current image (Bias voltage: 1 mV) and simulated LDOS map of the dimer in d. f dI/dV spectra and numerical calculated dI²/dV² spectra taken on the two locations marked in e. Two symmetric peaks have been detected, suggesting an antiferromagnetic coupled ground state with S = 0. The black dashed line is simulated line shape using a perturbative approach up to third order. Scale bars: 0.3 nm.