Recently, Professor Xu Nan's research group of the Institute for Advanced Study and Wu Fengcheng, Zhang Chendong and Yuan Shengjun of the School of Physical Science and Technology cooperated to achieve large-scale in situ controllable high-order molar effects for the first time in the world using angle-resolved photoelectron spectroscopy (ARPES) and in situ film growth regulation technology. The study was published online in Physical Review Letters.
The paper is entitled "Tailoring Dirac fermions byinsitutunable high-order moirépattern in graphene-monolayer xenon heterostructure". Wu Chunlong, a 2020 doctoral student and postdoctoral fellow Wan Qiang of the Institute for Advanced Study, are the co-first authors, Xu Nan and Wu Feng become the co-corresponding authors, and Wuhan University and the Wuhan Institute of Quantum Technology are the co-signatories of the paper.
The "molar effect" refers to a structure with greater periodicity produced by modulation between similar periodic structures. In recent years, it has been found that the molar effect generated by the stacking of low-dimensional materials can lead to a system with a strongly correlated narrowband electronic structure, which can realize a series of novel states of matter such as associated insulators, superconductivity, magnetism and non-banal topological states, providing a research platform for novel quantum states. The research on molar effects in the early stage mainly focused on low-dimensional material systems with the same or similar lattice constants, and the molar effect that is continuously adjustable in situ over a large period of time is a powerful tool for regulating quantum states that people pursue.
In recent years, Xu Nan and his collaborators have carried out a series of studies on "higher-order molar effects". In heterojunctions with large differences in lattice constants, the first-order molar effect is weaker. It is found that if the lattice supercellular constant of the system is similar, it has a strong higher-order molar effect, which in turn modulates the electronic structure. In previous studies, they proposed at the graphene-silicon carbide heterojunction that higher-order molar effects can lead to molar superstructures with a period of 1.9 nanometers, explaining the multiple Dirac replication bands newly observed in the ARPES experiment (Phys. Rev. B 104, 235130 (2020)).
Recently, by growing a xenon monoatomic layer in situ on a single layer of graphene and carrying out ARPES measurements, the research group achieved for the first time a large-scale adjustable high-order molar effect with a large range of molar periods in situ. By adjusting the lattice constant of the xenon single atomic layer by in-situ annealing, the period of the higher-order molar effect can be modulated from nanometer to infinity. ARPES observed the Dirac replication band near the center of the Brillouin district, which gradually approached and eventually coincided as the molar period became larger. The theoretical model points out that analogous to the interlayer interaction of Dirac fermions in corner graphene, the energy-valley coupling of Dirac fermions in graphene-xenon monoatomic layer heterojunctions can also lead to molar narrow bands under large molar periodic conditions, which is expected to achieve novel correlated electron states. This work has discovered a new platform to study the continuous evolution of molar fringes and provided a new method for modulating the energy-valley coupling of Dirac fermions.
Original link: 武汉大学新闻网- 我校学者实现原位可调控的高阶摩尔效应 (whu.edu.cn)
Artical link: Tailoring Dirac Fermions by In-Situ Tunable High-Order Moiré Pattern in Graphene-Monolayer Xenon Heterostructure (aps.org)
