Browsing by Author "Huang, Qingzhen"

Now showing 1 - 5 of 5
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    A Mott insulator continuously connected to iron pnictide superconductors
    (Springer Nature, 2016) Song, Yu; Yamani, Zahra; Cao, Chongde; Li, Yu; Zhang, Chenglin; Chen, Justin S.; Huang, Qingzhen; Wu, Hui; Tao, Jing; Zhu, Yimei; Tian, Wei; Chi, Songxue; Cao, Huibo; Huang, Yao-Bo; Dantz, Marcus; Schmitt, Thorsten; Yu, Rong; Nevidomskyy, Andriy H.; Morosan, Emilia; Si, Qimiao; Dai, Pengcheng; Rice Center for Quantum Materials
    Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe1−xCuxAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5, the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ∼x=0.05. Our discovery of a Mott-insulating state in NaFe1−xCuxAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-Tc superconductivity.
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    Diffusive excitonic bands from frustrated triangular sublattice in a singlet-ground-state system
    (Springer Nature, 2023) Gao, Bin; Chen, Tong; Wu, Xiao-Chuan; Flynn, Michael; Duan, Chunruo; Chen, Lebing; Huang, Chien-Lung; Liebman, Jesse; Li, Shuyi; Ye, Feng; Stone, Matthew B.; Podlesnyak, Andrey; Abernathy, Douglas L.; Adroja, Devashibhai T.; Duc Le, Manh; Huang, Qingzhen; Nevidomskyy, Andriy H.; Morosan, Emilia; Balents, Leon; Dai, Pengcheng
    Magnetic order in most materials occurs when magnetic ions with finite moments arrange in a particular pattern below the ordering temperature. Intriguingly, if the crystal electric field (CEF) effect results in a spin-singlet ground state, a magnetic order can still occur due to the exchange interactions between neighboring ions admixing the excited CEF levels. The magnetic excitations in such a state are spin excitons generally dispersionless in reciprocal space. Here we use neutron scattering to study stoichiometric Ni2Mo3O8, where Ni2+ ions form a bipartite honeycomb lattice comprised of two triangular lattices, with ions subject to the tetrahedral and octahedral crystalline environment, respectively. We find that in both types of ions, the CEF excitations have nonmagnetic singlet ground states, yet the material has magnetic order. Furthermore, CEF spin excitons from the tetrahedral sites form a dispersive diffusive pattern around the Brillouin zone boundary, likely due to spin entanglement and geometric frustrations.
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    Gradual enhancement of stripe-type antiferromagnetism in the spin-ladder material BaFe2S3 under pressure
    (American Physical Society, 2018) Zheng, Liangliang; Frandsen, Benjamin A.; Wu, Changwei; Yi, Ming; Wu, Shan; Huang, Qingzhen; Bourret-Courchesne, Edith; Simutis, G.; Khasanov, R.; Yao, Dao-Xin; Wang, Meng; Birgeneau, Robert J.
    We report pressure-dependent neutron diffraction and muon spin relaxation/rotation measurements combined with first-principles calculations to investigate the structural, magnetic, and electronic properties of BaFe2S3 under pressure. The experimental results reveal a gradual enhancement of the stripe-type ordering temperature with increasing pressure up to 2.6 GPa and no observable change in the size of the ordered moment. The ab initio calculations suggest that the magnetism is highly sensitive to the Fe-S bond lengths and angles, clarifying discrepancies with previously published results. In contrast to our experimental observations, the calculations predict a monotonic reduction of the ordered moment with pressure. We suggest that the robustness of the stripe-type antiferromagnetism is due to strong electron correlations not fully considered in the calculations.
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    Modulated magnetism and anomalous electronic transport in Ce3Cu4As4O2
    (American Physical Society, 2016) Wang, Jiakui K.; Wu, Shan; Qiu, Yiming; Rodriguez-Rivera, Jose A.; Huang, Qingzhen; Broholm, C.; Morosan, E.
    The complex magnetism and transport properties of tetragonal Ce3Cu4As4O2 were examined through neutron scattering and physical property measurements on polycrystalline samples. The lamellar structure consists of alternating layers of CeCu4As4 with a single square Ce lattice and Ce2O2 bilayers. Peaks in the specific heat at the Néel temperature TN=24 K, T2=16 K, and T3=1.9 K indicate three magnetic phase transitions or distinct crossover phenomena. For T
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    Topological Spin Excitations in Honeycomb Ferromagnet CrI3
    (American Physical Society, 2018) Chen, Lebing; Chung, Jae-Ho; Gao, Bin; Chen, Tong; Stone, Matthew B.; Kolesnikov, Alexander I.; Huang, Qingzhen; Dai, Pengcheng
    In two-dimensional honeycomb ferromagnets, bosonic magnon quasiparticles (spin waves) may either behave as massless Dirac fermions or form topologically protected edge states. The key ingredient defining their nature is the next-nearest-neighbor Dzyaloshinskii-Moriya interaction that breaks the inversion symmetry of the lattice and discriminates chirality of the associated spin-wave excitations. Using inelastic neutron scattering, we find that spin waves of the insulating honeycomb ferromagnet CrI3 (TC=61 K) have two distinctive bands of ferromagnetic excitations separated by a ∼4 meV gap at the Dirac points. These results can only be understood by considering a Heisenberg Hamiltonian with Dzyaloshinskii-Moriya interaction, thus providing experimental evidence that spin waves in CrI3 can have robust topological properties potentially useful for dissipationless spintronic applications.