Researchers Investigate Nematic Spin Correlations in Tetragonal State of Uniaxial-strained BaFe2-xNixAs2
Sep 25, 2014 Email"> PrintText Size
Understanding the electronic anisotropic state at a temperature associated with the nematic phase is one of the most important unresolved problems in the quest for mechanism of high-Tc superconductivity in iron pnictides. Upon warming to above the antiferromagneitc (AF) order (TN) and orthorhombic lattice distortion (Ts) temperatures, the iron pnictides become paramagnetic tetragonal metals, but still have anisotropic features in transport results within FeAs plane. Such electronic anisotropy is explained as orbital ordering or local impurity scattering. Since it breaks the 4-fold rotating (C4) symmetry, it is also taken as a strong evidence for electronic nematicity at high temperature. If this is indeed the case, one also would be expected spin nematicity in the tetragonal phase of iron pnictides.
Recently, Prof. DAI Pengcheng’s team from Beijing National Laboratory for Condensed Matter Physics at the Institute of Physics (IOP) of Chinese Academy of Sciences focused on the electron doped iron arsenide BaFe2−xNixAs2 and carried out polarized neutron scattering on the twinned single crystals. One key result is that the low-energy spin excitations in these materials is highly anisotropic within FeAs plane, and the spin anisotropy persists in the tetragonal phase well above Ts and TN corresponding to the onset of the in-plane resistivity anisotropy (H. Luo et al., Phys. Rev. Lett. 111, 107006 (2013)).
To further explore whether a spin nematicity exist in BaFe2−xNixAs2 system, LU Xingye, ZHANG Rui and LUO Huiqian of Prof. DAI Pengcheng’s group, in collaboration with J. T. Park from Heinz Maier-Leibnitz Zentrum Germany have done inelastic neutron scattering studies on detwinned BaFe2−xNixAs2 single crystals, with theoretical help from Prof. Nevidomskyy Andriy and Prof. SI Qimiao from Rice University. In the parent compound BaFe2As2 and underdoped sample BaFe1.915Ni0.085As2, they have found that the spin excitations develop an anisotropy in spectral weight between the Q= (±1, 0) and (0, ±1) positions at a higher temperature T* > Ts. It is also around this temperature that the resistivity measurements in detwinned crystals reveal anisotropy. While in the overdoped BaFe1.88Ni0.12As2 without resistivity anisotropy, the spin excitations are isotropic at all measured energies.
This is the first time to observe electronic nematicity in spin channel of iron-based superconductors. The results unveil the nematic spin correlations, establish that they are intrinsic and persist in the quantum fluctuation regime close to the optimally electron-doped iron pnictide superconductor.
This work was published on Science [X. Lu et. al., Science 345, 657(2014)]. It was supported by the National Basic Research Program of China (Grant No. 2012CB821400 and 2011CBA00110) and the National Science Foundation of China, together with other grants from USA.
Figure: The electronic phase diagram of BaFe2−xNixAs2 from resistivity anisotropy obtained under uniaxial pressure. The spin excitation anisotropy temperatures are marked as T*. The AF orthorhombic (Ort), incommensurate AF (IC) , paramagnetic tetragonal (PM Tet), and superconductivity (SC) phases are marked (Image by IOP)
Contact:
Prof. DAI Pengcheng
Institute of Physics, Chinese Academy of Sciences
Email: pcdai@iphy.ac.cn
Understanding the electronic anisotropic state at a temperature associated with the nematic phase is one of the most important unresolved problems in the quest for mechanism of high-Tc superconductivity in iron pnictides. Upon warming to above the antiferromagneitc (AF) order (TN) and orthorhombic lattice distortion (Ts) temperatures, the iron pnictides become paramagnetic tetragonal metals, but still have anisotropic features in transport results within FeAs plane. Such electronic anisotropy is explained as orbital ordering or local impurity scattering. Since it breaks the 4-fold rotating (C4) symmetry, it is also taken as a strong evidence for electronic nematicity at high temperature. If this is indeed the case, one also would be expected spin nematicity in the tetragonal phase of iron pnictides.
Recently, Prof. DAI Pengcheng’s team from Beijing National Laboratory for Condensed Matter Physics at the Institute of Physics (IOP) of Chinese Academy of Sciences focused on the electron doped iron arsenide BaFe2−xNixAs2 and carried out polarized neutron scattering on the twinned single crystals. One key result is that the low-energy spin excitations in these materials is highly anisotropic within FeAs plane, and the spin anisotropy persists in the tetragonal phase well above Ts and TN corresponding to the onset of the in-plane resistivity anisotropy (H. Luo et al., Phys. Rev. Lett. 111, 107006 (2013)).
To further explore whether a spin nematicity exist in BaFe2−xNixAs2 system, LU Xingye, ZHANG Rui and LUO Huiqian of Prof. DAI Pengcheng’s group, in collaboration with J. T. Park from Heinz Maier-Leibnitz Zentrum Germany have done inelastic neutron scattering studies on detwinned BaFe2−xNixAs2 single crystals, with theoretical help from Prof. Nevidomskyy Andriy and Prof. SI Qimiao from Rice University. In the parent compound BaFe2As2 and underdoped sample BaFe1.915Ni0.085As2, they have found that the spin excitations develop an anisotropy in spectral weight between the Q= (±1, 0) and (0, ±1) positions at a higher temperature T* > Ts. It is also around this temperature that the resistivity measurements in detwinned crystals reveal anisotropy. While in the overdoped BaFe1.88Ni0.12As2 without resistivity anisotropy, the spin excitations are isotropic at all measured energies.
This is the first time to observe electronic nematicity in spin channel of iron-based superconductors. The results unveil the nematic spin correlations, establish that they are intrinsic and persist in the quantum fluctuation regime close to the optimally electron-doped iron pnictide superconductor.
This work was published on Science [X. Lu et. al., Science 345, 657(2014)]. It was supported by the National Basic Research Program of China (Grant No. 2012CB821400 and 2011CBA00110) and the National Science Foundation of China, together with other grants from USA.
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| Figure: The electronic phase diagram of BaFe2−xNixAs2 from resistivity anisotropy obtained under uniaxial pressure. The spin excitation anisotropy temperatures are marked as T*. The AF orthorhombic (Ort), incommensurate AF (IC) , paramagnetic tetragonal (PM Tet), and superconductivity (SC) phases are marked (Image by IOP) |
Contact:
Prof. DAI Pengcheng
Institute of Physics, Chinese Academy of Sciences
Email: pcdai@iphy.ac.cn
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