Quantum Phase Transition in Magnetic Nanographenes on a Lead Superconductor

Yu Liu; Can Li; Fu-Hua Xue; Wei Su; Ying Wang; Haili Huang; Hao Yang; Jiayi Chen; Dandan Guan; Yaoyi Li; Hao Zheng; Canhua Liu; Mingpu Qin; Xiaoqun Wang; Rui Wang; Deng-Yuan Li; Pei-Nian Liu; Shiyong Wang; Jinfeng Jia

doi:10.1021/acs.nanolett.3c02208

Quantum Phase Transition in Magnetic Nanographenes on a Lead Superconductor

Nano Lett. 2023 Nov 8;23(21):9704-9710. doi: 10.1021/acs.nanolett.3c02208. Epub 2023 Oct 23.

Authors

Yu Liu^{1

2

3}, Can Li^{1

2

3}, Fu-Hua Xue⁴, Wei Su^{5

6}, Ying Wang⁴, Haili Huang^{1

2

3}, Hao Yang^{1

2

3}, Jiayi Chen^{1

2

3}, Dandan Guan^{1

2

3}, Yaoyi Li^{1

2

3}, Hao Zheng^{1

2

3}, Canhua Liu^{1

2

3}, Mingpu Qin¹, Xiaoqun Wang¹, Rui Wang^{7

8}, Deng-Yuan Li⁴, Pei-Nian Liu⁴, Shiyong Wang^{1

2

3}, Jinfeng Jia^{1

2

3}

Affiliations

¹ Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), TD Lee Institute, Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
² Hefei National Laboratory, Hefei 230088, China.
³ Shanghai Research Center for Quantum Sciences, 99 Xiupu Road, Shanghai 201315, China.
⁴ Key Laboratory for Advanced Materials and Feringa Nobel Prize Scientist Joint Research Center, Frontiers Science Center for Materiobiology and Dynamic Chemistry, State Key Laboratory of Chemical Engineering, School of Chemistry and Molecular Engineering, East China University of Science Technology, 130 Meilong Road, Shanghai 200237, China.
⁵ Beijing Computational Science Research Center, Beijing 100084, China.
⁶ College of Physics and Electronic Engineering, Center for Computational Sciences, Sichuan Normal University, Chengdu 610068, China.
⁷ National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China.
⁸ Collaborative Innovation Center for Advanced Microstructures, Nanjing 210093, China.

PMID: 37870505
DOI: 10.1021/acs.nanolett.3c02208

Abstract

Quantum spins, also known as spin operators that preserve SU(2) symmetry, lack a specific orientation in space and are hypothesized to display unique interactions with superconductivity. However, spin-orbit coupling and crystal field typically cause a significant magnetic anisotropy in d/f shell spins on surfaces. Here, we fabricate atomically precise S = 1/2 magnetic nanographenes on Pb(111) through engineering sublattice imbalance in the graphene honeycomb lattice. Through tuning the magnetic exchange strength between the unpaired spin and Cooper pairs, a quantum phase transition from the singlet to the doublet state has been observed, consistent with the quantum spin models. From our calculations, the particle-hole asymmetry is induced by the Coulomb scattering potential and gives a transition point about k_BT_k ≈ 1.6Δ. Our work demonstrates that delocalized π electron magnetism hosts highly tunable magnetic bound states, which can be further developed to study the Majorana bound states and other rich quantum phases of low-dimensional quantum spins on superconductors.

Keywords: Nanographene; Quantum phase transition; Superconductor; Yu-Shiba-Rusinov bound states.