Browsing by Author "Xie, Fang"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Emergent flat band and topological Kondo semimetal driven by orbital-selective correlations
    (Springer Nature, 2024) Chen, Lei; Xie, Fang; Sur, Shouvik; Hu, Haoyu; Paschen, Silke; Cano, Jennifer; Si, Qimiao
    Flat electronic bands are expected to show proportionally enhanced electron correlations, which may generate a plethora of novel quantum phases and unusual low-energy excitations. They are increasingly being pursued in d-electron-based systems with crystalline lattices that feature destructive electronic interference, where they are often topological. Such flat bands, though, are generically located far away from the Fermi energy, which limits their capacity to partake in the low-energy physics. Here we show that electron correlations produce emergent flat bands that are pinned to the Fermi energy. We demonstrate this effect within a Hubbard model, in the regime described by Wannier orbitals where an effective Kondo description arises through orbital-selective Mott correlations. Moreover, the correlation effect cooperates with symmetry constraints to produce a topological Kondo semimetal. Our results motivate a novel design principle for Weyl Kondo semimetals in a new setting, viz. d-electron-based materials on suitable crystal lattices, and uncover interconnections among seemingly disparate systems that may inspire fresh understandings and realizations of correlated topological effects in quantum materials and beyond.
  • Thumbnail Image
    Item
    Persistent flat band splitting and strong selective band renormalization in a kagome magnet thin film
    (Springer Nature, 2024) Ren, Zheng; Huang, Jianwei; Tan, Hengxin; Biswas, Ananya; Pulkkinen, Aki; Zhang, Yichen; Xie, Yaofeng; Yue, Ziqin; Chen, Lei; Xie, Fang; Allen, Kevin; Wu, Han; Ren, Qirui; Rajapitamahuni, Anil; Kundu, Asish K.; Vescovo, Elio; Kono, Junichiro; Morosan, Emilia; Dai, Pengcheng; Zhu, Jian-Xin; Si, Qimiao; Minár, Ján; Yan, Binghai; Yi, Ming; Smalley-Curl Institute
    Magnetic kagome materials provide a fascinating playground for exploring the interplay of magnetism, correlation and topology. Many magnetic kagome systems have been reported including the binary FemXn (X = Sn, Ge; m:n = 3:1, 3:2, 1:1) family and the rare earth RMn6Sn6 (R = rare earth) family, where their kagome flat bands are calculated to be near the Fermi level in the paramagnetic phase. While partially filling a kagome flat band is predicted to give rise to a Stoner-type ferromagnetism, experimental visualization of the magnetic splitting across the ordering temperature has not been reported for any of these systems due to the high ordering temperatures, hence leaving the nature of magnetism in kagome magnets an open question. Here, we probe the electronic structure with angle-resolved photoemission spectroscopy in a kagome magnet thin film FeSn synthesized using molecular beam epitaxy. We identify the exchange-split kagome flat bands, whose splitting persists above the magnetic ordering temperature, indicative of a local moment picture. Such local moments in the presence of the topological flat band are consistent with the compact molecular orbitals predicted in theory. We further observe a large spin-orbital selective band renormalization in the Fe $${{{{\rm{d}}}}}_{{xy}}+{{{{\rm{d}}}}}_{{x}^{2}-{y}^{2}}$$spin majority channel reminiscent of the orbital selective correlation effects in the iron-based superconductors. Our discovery of the coexistence of local moments with topological flat bands in a kagome system echoes similar findings in magic-angle twisted bilayer graphene, and provides a basis for theoretical effort towards modeling correlation effects in magnetic flat band systems.
  • Thumbnail Image
    Item
    Symmetry constraints and spectral crossing in a Mott insulator with Green's function zeros
    (American Physical Society, 2024) Setty, Chandan; Sur, Shouvik; Chen, Lei; Xie, Fang; Hu, Haoyu; Paschen, Silke; Cano, Jennifer; Si, Qimiao; Rice Center for Quantum Materials
    Lattice symmetries are central to the characterization of electronic topology. Recently, it was shown that Green's function eigenvectors form a representation of the space group. This formulation has allowed the identification of gapless topological states even when quasiparticles are absent. Here we demonstrate the profundity of the framework in the extreme case, when interactions lead to a Mott insulator, through a solvable model with long-range interactions. We find that both Mott poles and zeros are subject to the symmetry constraints, and relate the symmetry-enforced spectral crossings to degeneracies of the original noninteracting eigenstates. Our results lead to new understandings of topological quantum materials and highlight the utility of interacting Green's functions toward their symmetry-based design.