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Host: Prof. Hemian Yi
Venue: TDLI Meeting Room N400
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Meeting ID: 903721257, no password
Abstract:
Constructing novel quantum states via the engineering of various surface/interface superlattices has been a hot topic in condensed matter physics in recent years. Taking graphene as a representative example, the construction of Kekulé distortion with a (√3×√3)R30° superlattice periodicity can fold Dirac cones into the Brillouin zone center and open an energy gap. This report will introduce the construction of Kekulé superlattices and the regulation of Dirac fermions in graphene via multiple surface/interface element doping strategies.
Using angle-resolved photoemission spectroscopy (ARPES), we find that disordered impurities on the graphene surface can induce and enhance intervalley elastic scattering of Dirac electrons. Below the transition temperature, mutual interference among scattered Dirac electrons can form an ordered Kekulé superlattice state, thereby folding the two inequivalent Dirac cones at the K/K’ points of the Brillouin zone into the zone center [1]. For potassium (K) adsorbed on the surface, which exhibits heavy electron doping effects, prominent plasmons are generated, renormalizing the Dirac bands and suppressing the folding of Dirac cones [2]. Gadolinium (Gd) intercalation at the interface of epitaxial graphene can enhance its surface adsorption capability, facilitating the formation of Kekulé periodicity and band folding via nitrogen adsorption at low temperatures [3]. Ordered europium (Eu) intercalation at the interface of epitaxial graphene directly forms a Kekulé superlattice. More importantly, we discover that during band folding process, the folding Dirac fermions in graphene undergo strong exchange coupling with the local magnetic moments of Eu 4f orbital, inducing significant splitting of the folded Dirac bands [4].
This exchange coupling between Dirac electrons and local magnetic moments provides a new degree of freedom for regulating Dirac fermions. This giant splitting of folded Dirac bands holds significant scientific importance for advancing the practical applications of Kekulé graphene in spintronics, as well as exploring novel quantum states arising from Dirac electron correlations.
References：
[1] Can Wang*, Yi Zhang*, et al. Nano Letters 21(19), 8258-8265 (2021);
[2] Can Wang*, Yi Zhang*, et al. The Journal of Physical Chemistry Letters 13(40), 9396-9403 (2022);
[3] Can Wang*, Yi Zhang*, et al. The Journal of Physical Chemistry Letters 14(32), 7149-7156 (2023);
[4] Xiaodong Qiu, Can Wang*, Huaiqiang Wang*, Yi Zhang*, et al. The Journal of Physical Chemistry Letters 17(10), 2785-2791 (2026);
Biography:
Yi Zhang is a Professor at the School of Physics, Nanjing University. He received his B.S. degree from Peking University in 2006 and earned his Ph.D. from the Institute of Physics, Chinese Academy of Sciences, in 2011. From 2011 to 2015, he conducted postdoctoral research at the Lawrence Berkeley National Laboratory and Stanford University, USA. In 2015, he joined the School of Physics, Nanjing University, under the National High-Level Overseas Talent Program.
His research focuses on molecular beam epitaxy growth of novel two-dimensional quantum materials, as well as the construction and manipulation of emergent low-dimensional quantum states. To date, he has published more than 60 peer-reviewed articles with an H-index of 30. He has presided over multiple national research projects, including the National Key R&D Program and key programs supported by the National Natural Science Foundation of China. He was listed as an Elsevier Highly Cited Chinese Researcher (2021–2025) and was selected as a Clarivate Highly Cited Researcher in 2023.