Tunable topological phases in nanographene-based spin-1/2 alternating-exchange Heisenberg chains

• URL: http://arxiv.org/abs/2402.13590v1
• Date: Wed, 21 Feb 2024 07:45:05 GMT
• Title: Tunable topological phases in nanographene-based spin-1/2 alternating-exchange Heisenberg chains
• Authors: Chenxiao Zhao, Gon\c{c}alo Catarina, Jin-Jiang Zhang, Jo\~ao C. G. Henriques, Lin Yang, Ji Ma, Xinliang Feng, Oliver Gr\"oning, Pascal Ruffieux, Joaqu\'in Fern\'andez-Rossier, Roman Fasel
• Abstract summary: We present a versatile platform enabling site-selective spin manipulation in many-body spin systems. Our findings are corroborated by theoretical calculations, opening promising avenues toward the development of spin-based quantum devices.
• Score: 8.1791518522452
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Unlocking the potential of topological order within many-body spin systems has long been a central pursuit in the realm of quantum materials. Despite extensive efforts, the quest for a versatile platform enabling site-selective spin manipulation, essential for tuning and probing diverse topological phases, has persisted. Here, we utilize on-surface synthesis to construct spin-1/2 alternating-exchange Heisenberg (AH) chains[1] with antiferromagnetic couplings $J_1$ and $J_2$ by covalently linking Clar's goblets -- nanographenes each hosting two antiferromagnetically-coupled unpaired electrons[2]. Utilizing scanning tunneling microscopy, we exert atomic-scale control over the spin chain lengths, parities and exchange-coupling terminations, and probe their magnetic response by means of inelastic tunneling spectroscopy. Our investigation confirms the gapped nature of bulk excitations in the chains, known as triplons[3]. Besides, the triplon dispersion relation is successfully extracted from the spatial variation of tunneling spectral amplitudes. Furthermore, depending on the parity and termination of chains, we observe varying numbers of in-gap $S=1/2$ edge spins, enabling the determination of the degeneracy of distinct topological ground states in the thermodynamic limit-either 1, 2, or 4. By monitoring interactions between these edge spins, we identify the exponential decay of spin correlations. Our experimental findings, corroborated by theoretical calculations, present a phase-controlled many-body platform, opening promising avenues toward the development of spin-based quantum devices.

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