Browsing by Author "Yang, Yi-feng"

Now showing 1 - 5 of 5
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    Effect of Nematic Order on the Low-Energy Spin Fluctuations in Detwinned BaFe1.935Ni0.065As2
    (American Physical Society, 2016) Zhang, Wenliang; Park, J.T.; Lu, Xingye; Wei, Yuan; Ma, Xiaoyan; Hao, Lijie; Dai, Pengcheng; Meng, Zi Yang; Yang, Yi-feng; Luo, Huiqian; Li, Shiliang
    The origin of nematic order remains one of the major debates in iron-based superconductors. In theories based on spin nematicity, one major prediction is that the spin-spin correlation length at (0,π) should decrease with decreasing temperature below the structural transition temperature Ts. Here, we report inelastic neutron scattering studies on the low-energy spin fluctuations in BaFe1.935Ni0.065As2 under uniaxial pressure. Both intensity and spin-spin correlation start to show anisotropic behavior at high temperature, while the reduction of the spin-spin correlation length at (0,π) happens just below Ts, suggesting the strong effect of nematic order on low-energy spin fluctuations. Our results favor the idea that treats the spin degree of freedom as the driving force of the electronic nematic order.
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    Electronic specific heat in BaFe2−xNixAs2
    (American Physical Society, 2016) Gong, Dongliang; Xie, Tao; Lu, Xingye; Ren, Cong; Shan, Lei; Zhang, Rui; Dai, Pengcheng; Yang, Yi-feng; Luo, Huiqian; Li, Shiliang
    We have systematically studied the low-temperature specific heat of the BaFe2−xNixAs2 single crystals covering the whole superconducting dome. Using the nonsuperconducting heavily overdoped x=0.3 sample as a reference for the phonon contribution to the specific heat, we find that the normal-state electronic specific heats in the superconducting samples may have a nonlinear temperature dependence, which challenges previous results in the electron-doped Ba-122 iron-based superconductors. A model based on the presence of ferromagnetic spin fluctuations may explain the data between x=0.1 and x=0.15, suggesting the important role of Fermi-surface topology in understanding the normal-state electronic states.
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    High-energy magnetic excitations from heavy quasiparticles in CeCu2Si2
    (Springer Nature, 2021) Song, Yu; Wang, Weiyi; Cao, Chongde; Yamani, Zahra; Xu, Yuanji; Sheng, Yutao; Löser, Wolfgang; Qiu, Yiming; Yang, Yi-feng; Birgeneau, Robert J.; Dai, Pengcheng
    Magnetic fluctuations is the leading candidate for pairing in cuprate, iron-based, and heavy fermion superconductors. This view is challenged by the recent discovery of nodeless superconductivity in CeCu2Si2, and calls for a detailed understanding of the corresponding magnetic fluctuations. Here, we mapped out the magnetic excitations in superconducting (S-type) CeCu2Si2 using inelastic neutron scattering, finding a strongly asymmetric dispersion for E ≲ 1.5 meV, which at higher energies evolves into broad columnar magnetic excitations that extend to E ≳ 5 meV. While low-energy magnetic excitations exhibit marked three-dimensional characteristics, the high-energy magnetic excitations in CeCu2Si2 are almost two-dimensional, reminiscent of paramagnons found in cuprate and iron-based superconductors. By comparing our experimental findings with calculations in the random-phase approximation,we find that the magnetic excitations in CeCu2Si2 arise from quasiparticles associated with its heavy electron band, which are also responsible for superconductivity. Our results provide a basis for understanding magnetism and superconductivity in CeCu2Si2, and demonstrate the utility of neutron scattering in probing band renormalization in heavy fermion metals.
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    Kondo destruction in a quantum paramagnet with magnetic frustration
    (American Physical Society, 2018) Zhang, Jiahao; Zhao, Hengcan; Lv, Meng; Hu, Sile; Isikawa, Yosikazu; Yang, Yi-feng; Si, Qimiao; Steglich, Frank; Sun, Peijie
    We report results of isothermal magnetotransport and susceptibility measurements at elevated magnetic fields B down to very low temperatures T on single crystals of the frustrated Kondo-lattice system CePdAl. They reveal a B∗(T) line within the paramagnetic part of the phase diagram. This line denotes a thermally broadened “small”–to-“large” Fermi-surface crossover which substantially narrows upon cooling. At B0∗=B∗(T=0)=(4.6±0.1)T, this B∗(T) line merges with two other crossover lines, viz. Tp(B) below and TFL(B) above B0∗. Tp characterizes a frustration-dominated spin-liquid state, while TFL is the Fermi-liquid temperature associated with the lattice Kondo effect. Non-Fermi-liquid phenomena which are commonly observed near a “Kondo-destruction” quantum-critical point cannot be resolved in CePdAl. Our observations reveal a rare case where Kondo coupling, frustration, and quantum criticality are closely intertwined.
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    Nematic Quantum Critical Fluctuations in BaFe2−xNixAs2
    (American Physical Society, 2016) Liu, Zhaoyu; Gu, Yanhong; Zhang, Wei; Gong, Dongliang; Zhang, Wenliang; Xie, Tao; Lu, Xingye; Ma, Xiaoyan; Zhang, Xiaotian; Zhang, Rui; Zhu, Jun; Ren, Cong; Shan, Lei; Qiu, Xianggang; Dai, Pengcheng; Yang, Yi-feng; Luo, Huiqian; Li, Shiliang
    We have systematically studied the nematic fluctuations in the electron-doped iron-based superconductor BaFe2−xNixAs2 by measuring the in-plane resistance change under uniaxial pressure. While the nematic quantum critical point can be identified through the measurements along the (110) direction, as studied previously, quantum and thermal critical fluctuations cannot be distinguished due to similar Curie-Weiss-like behaviors. Here we find that a sizable pressure-dependent resistivity along the (100) direction is present in all doping levels, which is against the simple picture of an Ising-type nematic model. The signal along the (100) direction becomes maximum at optimal doping, suggesting that it is associated with nematic quantum critical fluctuations. Our results indicate that thermal fluctuations from striped antiferromagnetic order dominate the underdoped regime along the (110) direction. We argue that either there is a strong coupling between the quantum critical fluctuations and the fermions, or more exotically, a higher symmetry may be present around optimal doping.