Browsing by Author "Li, Shiliang"
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Item Doping effects of Cr on the physical properties of BaFe1.9−xNi0.1CrxAs2(American Physical Society, 2018) Gong, Dongliang; Xie, Tao; Zhang, Rui; Birk, Jonas; Niedermayer, Christof; Han, Fei; Lapidus, S.H.; Dai, Pengcheng; Li, Shiliang; Luo, HuiqianWe present a systematic study on the heavily Cr doped iron pnictides BaFe1.9−xNi0.1CrxAs2 by using elastic neutron scattering, high-resolution synchrotron x-ray diffraction (XRD), resistivity, and Hall transport measurements. When the Cr concentration increases from x=0 to 0.8, neutron diffraction experiments suggest that the collinear antiferromagnetism persists in the whole doping range, where the Néel temperature TN coincides with the tetragonal-to-orthorhombic structural transition temperature Ts, and both of them keeps around 35 K. The magnetic ordered moment, on the other hand, increases within increasing x until x=0.5, and then decreases with further increasing x. Detailed refinement of the powder XRD patterns reveals that the Cr substitutions actually stretch the FeAs4 tetrahedron along the c axis and lift the arsenic height away from the Fe-Fe plane. Transport results indicate that the charge carriers become more localized upon Cr doping, then changes from electron type to hole type around x=0.5. Our results suggest that the ordered moment and the ordered temperature of static magnetism in iron pnictides can be decoupled and tuned separately by chemical doping.Item Doping evolution of antiferromagnetism and transport properties in nonsuperconducting BaFe2−2xNixCrxAs2(American Physical Society, 2015) Zhang, Rui; Gong, Dongliang; Lu, Xingye; Li, Shiliang; Laver, Mark; Niedermayer, Christof; Danilkin, Sergey; Deng, Guochu; Dai, Pengcheng; Luo, HuiqianWe report elastic neutron scattering and transport measurements on the Ni and Cr equivalently doped iron pnictide BaFe2−2xNixCrxAs2. Compared with the electron-doped BaFe2−xNixAs2, the long-range antiferromagnetic (AF) order in BaFe2−2xNixCrxAs2 is gradually suppressed with vanishing ordered moment and Néel temperature near x=0.20 without the appearance of superconductivity. A detailed analysis on the transport properties of BaFe2−xNixAs and BaFe2−2xNixCrxAs2 suggests that the non-Fermi-liquid behavior associated with the linear resistivity as a function of temperature may not correspond to the disappearance of the static AF order. From the temperature dependence of the resistivity in overdoped compounds without static AF order, we find that the transport properties are actually affected by Cr impurity scattering, which may induce a metal-to-insulator crossover in highly doped BaFe1.7−yNi0.3CryAs2.Item Doping evolution of antiferromagnetism and transport properties in nonsuperconducting BaFe2−2xNixCrxAs2(American Physical Society, 2015) Zhang, Rui; Gong, Dongliang; Lu, Xingye; Li, Shiliang; Laver, Mark; Niedermayer, Christof; Danilkin, Sergey; Deng, Guochu; Dai, Pengcheng; Luo, HuiqianWe report elastic neutron scattering and transport measurements on the Ni and Cr equivalently doped iron pnictide BaFe2−2xNixCrxAs2. Compared with the electron-doped BaFe2−xNixAs2, the long-range antiferromagnetic (AF) order in BaFe2−2xNixCrxAs2 is gradually suppressed with vanishing ordered moment and Néel temperature near x=0.20 without the appearance of superconductivity. A detailed analysis on the transport properties of BaFe2−xNixAs and BaFe2−2xNixCrxAs2 suggests that the non-Fermi-liquid behavior associated with the linear resistivity as a function of temperature may not correspond to the disappearance of the static AF order. From the temperature dependence of the resistivity in overdoped compounds without static AF order, we find that the transport properties are actually affected by Cr impurity scattering, which may induce a metal-to-insulator crossover in highly doped BaFe1.7−yNi0.3CryAs2.Item 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, ShiliangThe 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.Item Electron doping evolution of structural and antiferromagnetic phase transitions in NaFe1−xCoxAs iron pnictides(American Physical Society, 2016) Tan, Guotai; Song, Yu; Zhang, Chenglin; Lin, Lifang; Xu, Zhuang; Hou, Tingting; Tian, Wei; Cao, Huibo; Li, Shiliang; Feng, Shiping; Dai, PengchengWe use transport and neutron diffraction to study the electronic phase diagram of NaFe1−xCoxAs. In the undoped state, NaFeAs exhibits a tetragonal-to-orthorhombic structural transition below Tsfollowed by a collinear antiferromagnetic (AF) order below TN. Upon codoping to form NaFe1−xCoxAs,Ts and TN are gradually suppressed, leading to optimal superconductivity near Co-doping x=0.025. While transport experiments on these materials reveal an anomalous behavior suggesting the presence of a quantum critical point (QCP) near optimal superconductivity, our neutron diffraction results indicate that commensurate AF order becomes transversely incommensurate with TN>Tc before vanishing abruptly at optimal superconductivity. These results are remarkably similar to electron-doping and isovalent-doping evolution of the AF order in BaFe2−xNixAs2 and BaFe2(As1−xPx)2, thus suggesting a universal behavior in the suppression of the magnetic order in iron pnictides as superconductivity is induced.Item 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, ShiliangWe 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.Item Excess-iron driven spin glass phase in Fe1 + yTe1 - xSex(IOP Publishing Ltd, 2021) Tian, Long; Liu, Panpan; Hong, Tao; Seydel, Tilo; Lu, Xingye; Luo, Huiqian; Li, Shiliang; Dai, PengchengThe iron-chalcogenide superconductor FeTe1–xSex displays a variety of exotic features distinct from iron pnictides. Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x = 0.5, the existence of a spin glass phase with short-range magnetic order in the doping range (x ∼ 0.1–0.3) has rarely been studied. Here, we use DC/AC magnetization and (quasi) elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe1.07Te0.8Se0.2 sample. The AC-frequency dependent spin-freezing temperature Tf generates a frequency sensitivity ΔTf(ω)/[Tf(ω)Δlog10 ω] ≈ 0.028 and the description of the critical slowing down with τ = τ0(Tf/TSG – 1)−z v gives TSG ≈ 22 K and zv ≈ 10, comparable to that of a classical spin-glass system. We have also extended the frequency-dependent Tf to the smaller time scale using energy-resolution-dependent neutron diffraction measurements, in which the TN of the short-range magnetic order increases systematically with increasing energy resolution. By removing the excess iron through annealing in oxygen, the spin-freezing behavior disappears, and bulk superconductivity is realized. Thus, the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity.Item Impact of uniaxial pressure on structural and magnetic phase transitions in electron-doped iron pnictides(American Physical Society, 2016) Lu, Xingye; Tseng, Kuo-Feng; Keller, T.; Zhang, Wenliang; Hu, Ding; Song, Yu; Man, Haoran; Park, J.T.; Luo, Huiqian; Li, Shiliang; Nevidomskyy, Andriy H.; Dai, PengchengWe use neutron resonance spin echo and Larmor diffraction to study the effect of uniaxial pressure on the tetragonal-to-orthorhombic structural (Ts) and antiferromagnetic (AF) phase transitions in iron pnictides BaFe2−xNixAs2 (x=0,0.03,0.12),SrFe1.97Ni0.03As2, and BaFe2(As0.7P0.3)2. In antiferromagnetically ordered BaFe2−xNixAs2 and SrFe1.97Ni0.03As2 with TN and Ts (TN≤Ts), a uniaxial pressure necessary to detwin the sample also increases TN, smears out the structural transition, and induces an orthorhombic lattice distortion at all temperatures. By comparing temperature and doping dependence of the pressure induced lattice parameter changes with the elastoresistance and nematic susceptibility obtained from transport and ultrasonic measurements, we conclude that the in-plane resistivity anisotropy found in the paramagnetic state of electron underdoped iron pnictides depends sensitively on the nature of the magnetic phase transition and a strong coupling between the uniaxial pressure induced lattice distortion and electronic nematic susceptibility.Item Long-range two-dimensional superstructure in the superconducting electron-doped cuprate Pr0.88LaCe0.12CuO4(American Physical Society, 2015) Campbell, B.J.; Rosenkranz, S.; Kang, H.J.; Stokes, H.T.; Chupas, P.J.; Komiya, S.; Ando, Y.; Li, Shiliang; Dai, PengchengUtilizing single-crystal synchrotron x-ray scattering, we observe distorted CuO2 planes in the electron-doped superconductor Pr1−xLaCexCuO4+δ, x = 0.12. Resolution-limited rods of scattering are indicative of a long-range two-dimensional 22√×22√ superstructure in the a−b plane, adhering to planar space-group symmetry p4gm, which is subject to stacking disorder perpendicular to the planes. This superstructure is present only in annealed, superconducting samples, but not in the as-grown, nonsuperconducting samples. These long-range distortions of the CuO2 planes, which are generally considered to be detrimental to superconductivity, have avoided detection to date due to the challenges of observing and interpreting subtle diffuse-scattering features.Item Nematic Fluctuations in the Non-Superconducting Iron Pnictide BaFe1.9−xNi0.1CrxAs2(Frontiers Media S.A., 2022) Gong, Dongliang; Yi, Ming; Wang, Meng; Xie, Tao; Zhang, Wenliang; Danilkin, Sergey; Deng, Guochu; Liu, Xinzhi; Park, Jitae T.; Ikeuchi, Kazuhiko; Kamazawa, Kazuya; Mo, Sung-Kwan; Hashimoto, Makoto; Lu, Donghui; Zhang, Rui; Dai, Pengcheng; Birgeneau, Robert J.; Li, Shiliang; Luo, Huiqian; Rice Center for Quantum MaterialsThe main driven force of the electronic nematic phase in iron-based superconductors is still under debate. Here, we report a comprehensive study on the nematic fluctuations in a non-superconducting iron pnictide system BaFe1.9−xNi0.1CrxAs2 by electronic transport, angle-resolved photoemission spectroscopy (ARPES), and inelastic neutron scattering (INS) measurements. Previous neutron diffraction and transport measurements suggested that the collinear antiferromagnetism persists to x = 0.8, with similar Néel temperature TN and structural transition temperature Ts around 32 K, but the charge carriers change from electron type to hole type around x = 0.5. In this study, we have found that the in-plane resistivity anisotropy also highly depends on the Cr dopings and the type of charge carriers. While ARPES measurements suggest possibly weak orbital anisotropy onset near Ts for both x = 0.05 and x = 0.5 compounds, INS experiments reveal clearly different onset temperatures of low-energy spin excitation anisotropy, which is likely related to the energy scale of spin nematicity. These results suggest that the interplay between the local spins on Fe atoms and the itinerant electrons on Fermi surfaces is crucial to the nematic fluctuations of iron pnictides, where the orbital degree of freedom may behave differently from the spin degree of freedom, and the transport properties are intimately related to the spin dynamics.Item 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, ShiliangWe 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.Item Phase diagram and neutron spin resonance of superconducting NaFe1−xCuxAs(American Physical Society, 2017) Tan, Guotai; Song, Yu; Zhang, Rui; Lin, Lifang; Xu, Zhuang; Tian, Long; Chi, Songxue; Graves-Brook, M.K.; Li, Shiliang; Dai, PengchengWe use transport and neutron scattering to study the electronic phase diagram and spin excitations of NaFe1−xCuxAs single crystals. Similar to Co- and Ni-doped NaFeAs, a bulk superconducting phase appears near x≈2% with the suppression of stripe-type magnetic order in NaFeAs. Upon further increasing Cu concentration the system becomes insulating, culminating in an antiferromagnetically ordered insulating phase near x≈50%. Using transport measurements, we demonstrate that the resistivity in NaFe1−xCuxAs exhibits non-Fermi-liquid behavior near x≈1.8%. Our inelastic neutron scattering experiments reveal a single neutron spin resonance mode exhibiting weak dispersion along c axis in NaFe0.98Cu0.02As. The resonance is high in energy relative to the superconducting transition temperature Tc but weak in intensity, likely resulting from impurity effects. These results are similar to other iron pnictides superconductors despite that the superconducting phase in NaFe1−xCuxAs is continuously connected to an antiferromagnetically ordered insulating phase near x≈50% with significant electronic correlations. Therefore, electron correlations is an important ingredient of superconductivity in NaFe1−xCuxAs and other iron pnictides.Item Spin excitation anisotropy in the optimally isovalent-doped superconductor BaFe2(As0.7P0.3)2(American Physical Society, 2017) Hu, Ding; Zhang, Wenliang; Wei, Yuan; Roessli, Bertrand; Skoulatos, Markos; Regnault, Louis Pierre; Chen, Genfu; Song, Yu; Luo, Huiqian; Li, Shiliang; Dai, PengchengWe use neutron polarization analysis to study spin excitation anisotropy in the optimally isovalent-doped superconductor BaFe2(As0.7P0.3)2 (Tc=30 K). Different from optimally hole- and electron-doped BaFe2As2, where there is a clear spin excitation anisotropy in the paramagnetic tetragonal state well above Tc, we find no spin excitation anisotropy for energies above 2 meV in the normal state of BaFe2(As0.7P0.3)2. Upon entering the superconducting state, significant spin excitation anisotropy develops at the antiferromagnetic (AF) zone center QAF=(1,0,L=odd), while the magnetic spectrum is isotropic at the zone boundary Q=(1,0,L=even). By comparing the temperature, wave vector, and polarization dependence of the spin excitation anisotropy in BaFe2(As0.7P0.3)2 and hole-doped Ba0.67K0.33Fe2As2 (Tc=38 K), we conclude that such anisotropy arises from spin-orbit coupling and is associated with the nearby AF order and superconductivity.Item Spin excitations in optimally P-dopedﾠBaFe2(As0.7P0.3)2 superconductor(American Physical Society, 2016) Hu, Ding; Yin, Zhiping; Zhang, Wenliang; Ewings, R.A.; Ikeuchi, Kazuhiko; Nakamura, Mitsutaka; Roessli, Bertrand; Wei, Yuan; Zhao, Lingxiao; Chen, Genfu; Li, Shiliang; Luo, Huiqian; Haule, Kristjan; Kotliar, Gabriel; Dai, PengchengWe use inelastic neutron scattering to study the temperature and energy dependence of spin excitations in an optimally P-doped BaFe2(As0.7P0.3)2 superconductor (Tc=30 K) throughout the Brillouin zone. In the undoped state, spin waves and paramagnetic spin excitations of BaFe2As2stem from an antiferromagnetic (AF) ordering wave vector QAF=(±1,0), and peak near the zone boundary at (±1,±1) around 180 meV. Replacing 30% As by smaller P to induce superconductivity, low-energy spin excitations of BaFe2(As0.7P0.3)2 form a resonance in the superconducting state and high-energy spin excitations now peak around 220 meV near (±1,±1). These results are consistent with calculations from a combined density functional theory and dynamical mean field theory, and suggest that the decreased average pnictogen height in BaFe2(As0.7P0.3)2 reduces the strength of electron correlations and increases the effective bandwidth of magnetic excitations.Item Structural and Magnetic Phase Transitions near Optimal Superconductivity in BaFe2(As1−xPx)2(American Physical Society, 2015) Hu, Ding; Lu, Xingye; Zhang, Wenliang; Luo, Huiqian; Li, Shiliang; Wang, Peipei; Chen, Genfu; Han, Fei; Banjara, Shree R.; Sapkota, A.; Kreyssig, A.; Goldman, A.I.; Yamani, Z.; Niedermayer, Christof; Skoulatos, Markos; Georgii, Robert; Keller, T.; Wang, Pengshuai; Yu, Weiqiang; Dai, PengchengWe use nuclear magnetic resonance (NMR), high-resolution x-ray, and neutron scattering studies to study structural and magnetic phase transitions in phosphorus-doped BaFe2(As1−xPx)2. Previous transport, NMR, specific heat, and magnetic penetration depth measurements have provided compelling evidence for the presence of a quantum critical point (QCP) near optimal superconductivity at x=0.3. However, we show that the tetragonal-to-orthorhombic structural (Ts) and paramagnetic to antiferromagnetic (AF, TN) transitions in BaFe2(As1−xPx)2 are always coupled and approach TN≈Ts≥Tc (≈29 K) for x=0.29 before vanishing abruptly for x≥0.3. These results suggest that AF order in BaFe2(As1−xPx)2 disappears in a weakly first-order fashion near optimal superconductivity, much like the electron-doped iron pnictides with an avoided QCP.Item Temperature and polarization dependence of low-energy magnetic fluctuations in nearly optimally doped NaFe0.9785Co0.0215As(American Physical Society, 2017) Song, Yu; Wang, Weiyi; Zhang, Chenglin; Gu, Yanhong; Lu, Xingye; Tan, Guotai; Su, Yixi; Bourdarot, Frédéric; Christianson, A.D.; Li, Shiliang; Dai, PengchengWe use unpolarized and polarized neutron scattering to study the temperature and polarization dependence of low-energy magnetic fluctuations in nearly optimally doped NaFe0.9785Co0.0215As, with coexisting superconductivity (Tc≈19 K) and weak antiferromagnetic order (TN≈30 K, ordered moment ≈0.02μB/Fe). A single spin resonance mode with intensity tracking the superconducting order parameter is observed, although energy of the mode only softens slightly upon approaching Tc. Polarized neutron scattering reveals that the single resonance is mostly isotropic in spin space, similar to overdoped NaFe0.935Co0.045As but different from optimal electron-, hole-, and isovalently doped BaFe2As2 compounds, all featuring an additional prominent anisotropic component. Spin anisotropy in NaFe0.9785Co0.0215As is instead present at energies below the resonance, which becomes partially gapped below Tc, similar to the situation in optimally doped YBa2Cu3O6.9. Our results indicate that anisotropic spin fluctuations in NaFe1−xCoxAs appear in the form of a resonance in the underdoped regime, become partially gapped below Tc near optimal doping, and disappear in overdoped compounds.