Browsing by Author "Hu, Haoyu"

Now showing 1 - 7 of 7
  • Thumbnail Image
    Item
    Coupled topological flat and wide bands: Quasiparticle formation and destruction
    (AAAS, 2023) Hu, Haoyu; Si, Qimiao
    Flat bands amplify correlation effects and are of extensive current interest. They provide a platform to explore both topology in correlated settings and correlation physics enriched by topology. Recent experiments in correlated kagome metals have found evidence for strange-metal behavior. A major theoretical challenge is to study the effect of local Coulomb repulsion when the band topology obstructs a real-space description. In a variant to the kagome lattice, we identify an orbital-selective Mott transition in any system of coupled topological flat and wide bands. This was made possible by the construction of exponentially localized and Kramers-doublet Wannier functions, which, in turn, leads to an effective Kondo-lattice description. Our findings show how quasiparticles are formed in such coupled topological flat-wide band systems and, equally important, how they are destroyed. Our work provides a conceptual framework for the understanding of the existing and emerging strange-metal properties in kagome metals and beyond.
  • 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
    Inhomogeneous Kondo-lattice in geometrically frustrated Pr2Ir2O7
    (Springer Nature, 2021) Kavai, Mariam; Friedman, Joel; Sherman, Kyle; Gong, Mingda; Giannakis, Ioannis; Hajinazar, Samad; Hu, Haoyu; Grefe, Sarah E.; Leshen, Justin; Yang, Qiu; Nakatsuji, Satoru; Kolmogorov, Aleksey N.; Si, Qimiao; Lawler, Michael; Aynajian, Pegor; Rice Center for Quantum Materials
    Magnetic fluctuations induced by geometric frustration of local Ir-spins disturb the formation of long-range magnetic order in the family of pyrochlore iridates. As a consequence, Pr2Ir2O7 lies at a tuning-free antiferromagnetic-to-paramagnetic quantum critical point and exhibits an array of complex phenomena including the Kondo effect, biquadratic band structure, and metallic spin liquid. Using spectroscopic imaging with the scanning tunneling microscope, complemented with machine learning, density functional theory and theoretical modeling, we probe the local electronic states in Pr2Ir2O7 and find an electronic phase separation. Nanoscale regions with a well-defined Kondo resonance are interweaved with a non-magnetic metallic phase with Kondo-destruction. These spatial nanoscale patterns display a fractal geometry with power-law behavior extended over two decades, consistent with being in proximity to a critical point. Our discovery reveals a nanoscale tuning route, viz. using a spatial variation of the electronic potential as a means of adjusting the balance between Kondo entanglement and geometric frustration.
  • Thumbnail Image
    Item
    Orbital Selectivity in Electron Correlations and Superconducting Pairing of Iron-Based Superconductors
    (Frontiers Media S.A., 2021) Yu, Rong; Hu, Haoyu; Nica, Emilian M.; Zhu, Jian-Xin; Si, Qimiao; Center for Quantum Materials
    Electron correlations play a central role in iron-based superconductors. In these systems, multiple Fe $3d$-orbitals are active in the low-energy physics, and they are not all degenerate. For these reasons, the role of orbital-selective correlations has been an active topic in the study of the iron-based systems. In this paper, we survey the recent developments on the subject. For the normal state, we emphasize the orbital-selective Mott physics that has been extensively studied, especially in the iron chalcogenides, in the case of electron filling $n \sim 6$. In addition, the interplay between orbital selectivity and electronic nematicity is addressed. For the superconducting state, we summarize the initial ideas for orbital-selective pairing, and discuss the recent explosive activities along this direction. We close with some perspectives on several emerging topics. These include the evolution of the orbital-selective correlations, magnetic and nematic orders and superconductivity as the electron filling factor is reduced from $6$ to $5$, as well as the interplay between electron correlations and topological bandstructure in iron-based superconductors.
  • Thumbnail Image
    Item
    Orbital-selective superconductivity in the nematic phase of FeSe
    (American Physical Society, 2018) Hu, Haoyu; Yu, Rong; Nica, Emilian M.; Zhu, Jian-Xin; Si, Qimiao
    The interplay between electronic orders and superconductivity is central to the physics of unconventional superconductors, and is particularly pronounced in the iron-based superconductors. Motivated by recent experiments on FeSe, we study the superconducting pairing in its nematic phase in a multiorbital model with frustrated spin-exchange interactions. Electron correlations in the presence of nematic order give rise to an enhanced orbital selectivity in the superconducting pairing amplitudes. This orbital-selective pairing produces a large gap anisotropy on the Fermi surface. Our results naturally explain the striking experimental observations, and shed light on the unconventional superconductivity of correlated electron systems in general.
  • Thumbnail Image
    Item
    Strongly correlated electron systems: Quantum criticality, unconventional superconductivity, and topology
    (2022-04-22) Hu, Haoyu; Si, Qimiao
    In many-electron systems, strong correlations lead to a rich variety of quantum phases and exotic phenomena. In this thesis, we investigate several such effects, including quantum criticality, unconventional superconductivity, and topology. Three general directions of investigation have been pursued. The first direction focuses on the Kondo-destruction quantum critical point of heavy-fermion metals, a prototype class of systems with strong correlations. We demonstrate non-trivial Kondo entanglement and dynamical scaling in the spin susceptibility. In addition, we show that robust superconductivity develops out of the quantum critical normal state that features a large-to-small Fermi-surface transformation. The second direction of research explores the interplay between electron correlations and topology. We find that a charge-spin intertwined phase is stabilized by the cooperation of topology and correlations. Furthermore, we analyze topological phases in the non-Fermi liquid context. Via interacting Green’s function, we determine the constraint of space-group symmetry on correlated topology and identify a gapless topological state without free-electron counterpart. Finally, we investigate the correlation effect in different multiorbital systems, including iron-based superconductors, UTe2, and moir´e graphene.
  • 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.