Recently, Prof. Li Fengyu and Research Fellow Wang Lei of the School of Physical Science and Technology of IMU have guided their postgraduates to make progress in searching for two-dimensional proper topological materials with superconductivity. The research results titled “Two-dimensional potassium borides with hidden kagome-like lattice: Topological semimetals, van Hove singularities, and superconductivity”, have been published in the top physical journal-Physical Review B .(Url of the article: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.107.235154 ).

Fig. 1 The first page of the article

The coexistence of nontrivial topological properties and superconductivity in a material offers the potential to achieve topological superconductivity and Majorana zero modes. However, research on ideal topological semimetals with superconductivity has been limited. This is because ideal topological semimetals have pure Dirac/Weyl fermions near the Fermi energy and do not have other quasi particles or states. As a result, the state density near Fermi energy level is very low. To realize the BSC superconductors with higher superconducting transition temperature, higher density of states is necessary near Fermi energy. Interestingly, Kagome-like lattice intrinsically have van Hove singularities, which results in high density of states. The engineering of the Kagome-like lattice can lead to topological superconducting materials with high superconducting transition temperature.

Fig. 2 Crystal structure diagram of four K-B materials

With the combination of the first principle and the global structure search, the research predicts new two-dimensional superconducting K-B materials with topological state. With the regulation of the ratio of atom K and the B9 monolayer, van Hove singularities of the hidden Kagome-like lattice can be regulated to the vicinity of Fermi surface to improve the density of electronic states of Fermi level of the materials and realize simultaneously the topology and superconductivity in the system. This research not only sheds light on the pivotal role played by the orbital character of the B9 layer in the kagome-like lattice of potassium borides but also presents a strategy for achieving the coexistence of topological properties and superconductivity, thereby opening up possibilities for the realization of exotic physics.

Fig. 3 (a) KB18, (b) KB9, (c) K2B9、(d) B9 and (e) diagram of projection energy band structure of hexagonal lattice and density of electronic states (f) The first Brillouin zone of five chemical compounds and diagram of the one-dimension projection Brillouin zone in the (01) direction

Fig. 4 (a) px+py orbital projection energy band within the B9 monolayer (b) pz orbital projection energy band within the B9 monolayer (c)(d) K-point projection of wave function of graphene-like and hidden Kagome-like flat band  (e)(f) The contrast of tight-binding-model-based graphene energy band and Kagome flat band with B9 monolayer energy band (g) projection energy band of p orbital within KB9 monolayer (h) The structure of three-dimensional energy band within KB9 monolayer (i) Fermi surface within KB9 monlayer and projection of surface state in the (01) direction

Fig. 5 The changing curve of transferred charges(from atom K to B9 monolayer), density of state near Fermi level[N(EF)], electron-phonon coupling constant(λ), superconducting transition temperature(Tc) and energy difference between van Hove singularities(EvHS) and Fermi level(EF) with the changing ratio of atom K and monolayer B9

Han Ting, a PhD student who was admitted to IMU in 2019 and Wang Shuaiyu, a master student who was admitted to IMU in 2021, are the first authors of the article. Prof. Li Fengyu and Research Fellow Wang Lei are the co-corresponding authors of the article. The research has been supported by the National Natural Science Foundation of China, the Natural Science Foundation of Inner Mongolia, the Grassland Talents Program of Inner Mongolia, Steed Program of Inner Mongolia University and Program of Inner Mongolia University for the Cultivation of Young Scientists.

A brief introduction to major authors:

Han Ting, a PhD student who was admitted to IMU in 2019, focuses on the research on the superconducting properties of two-dimensional materials. She has published as the sole first author or co-first authors 2 SCI articles in the international top journals-PRB and PCCP. Wang Shuaiyu, a master student who was admitted to IMU in 2021, concentrates on the topological properties of two-dimensional materials. He has published 2 articles in the international top journals-PRB and JPCC.

Li Fengyu, professor and supervisor of PhD students, focuses on the simulation and design of low-dimensional nanomaterials. Li has published over 70 articles in such international journals as JACS, ACIE, ACS Catal., PRB, JMCA, which have been cited more than 3300 times and whose H-index is 29. Many of his articles are selected as cover articles of journals and forwarded by scientific research media. He is one of the young editorial board members of J Mater Inf and Adv Powder Mater, guest editor of JMI, Nanomaterials and Catalysts, independent reviewer of such international journals as Nat. Commun., Adv. Sci., Small, JMCA. He has been selected as the excellent reviewer of JMCA, included in the Grassland Talents Program of Inner Mongolia and won the award of JMI for the young editors’ contribution.

Wang Lei, research fellow and PhD student supervisor, mainly conducts research on the computational condensed matter physics. Wang focuses on studying topological electron and phonon materials, low-dimensional nanomaterials of electronic information(superconducting materials, structural phase-changing materials and magnetic materials). He has published over 20 articles in such international journals as Science, National Science Review, Nature Communications, Physical Review B, Physical Review Materials, The Journal of Physical Chemistry C, which have been cited more than 900 times. Two of these articles are included in the highly-cited article of ESI. He is one of the reviewers of Physical Review B and Physical Review Materials.