We synthesize a series of Mn substituted （Li, Fe）OHFeSe superconductor single crystals via a modified ion-exchange method, with the Mn concentration z （the atomic ratio of Mn：Se） ranging from 0 to 0.07. The distr...We synthesize a series of Mn substituted （Li, Fe）OHFeSe superconductor single crystals via a modified ion-exchange method, with the Mn concentration z （the atomic ratio of Mn：Se） ranging from 0 to 0.07. The distribution homogeneity of the Mn element incorporated into the lattice of （Li, Fe）OHFeSe is checked by combined measurements of high-angle- annular-dark-field （HAADF） imaging and electron energy-loss spectroscopy （EELS）. Interestingly, we find that the superconducting transition temperature Tc and unit cell parameter c of the Mn-doped （Li, Fe）OHFeSe samples display similar V-shaped evolutions with the increasing dopant concentration z. We propose that, with increasing doping level, the Mn dopant first occupies the tetrahedral sites in the （Li, Fe）OH layers before starting to substitute the Fe element in the su- perconducting FeSe layers, which accounts for the V-shaped change in cell parameter c. The observed positive correlation between the Tc and lattice parameter c, regardless of the Mn doping level z, indicates that a larger interlayer separation, or a weaker interlayer coupling, is essential for the high-Tc superconductivity in （Li, Fe）OHFeSe. This agrees with our previous observations on powder, single crystal, and film samples of （Li, Fe）OHFeSe superconductors.展开更多
Mossbauer spectroscopy was used to probe the site-specific information of a K0.84Fe1.99Se2 superconductor. A spin excitation gap, △E≈5.5 meV, is observed by analyzing the temperature dependence of the hyperfine magn...Mossbauer spectroscopy was used to probe the site-specific information of a K0.84Fe1.99Se2 superconductor. A spin excitation gap, △E≈5.5 meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field （HMF） at the iron site within the spin wave theory. Using the simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the alkali metal intercalated iron selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure.展开更多
We study numerically the phase diagram for s and d-wave fermionic superftuidity/superconductivity with spin-dependent band- width imbalance on a two-dimensional square-lattice. We also investigate the spontaneous spac...We study numerically the phase diagram for s and d-wave fermionic superftuidity/superconductivity with spin-dependent band- width imbalance on a two-dimensional square-lattice. We also investigate the spontaneous space symmetry breaking states at low temperatures by solving the Bogoliubov-de Gennes equations. It is found that, the spatial configuration of the order parameter, both the uni-directional Fulde-Ferrell-Larkin-Ovchinnikov （FFLO） states and the two-dimensional FFLO state may show up in the presence of finite spin-dependent bandwidth imbalance. Moreover, we calculate the spectra of local density of states, and the experimental proposals of observing such FFLO states are therefore suggested.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0303003 and 2016YFA0300300)the National Natural Science Foundation of China(Grant No.11574370)the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant Nos.QYZDY-SSW-SLH001,QYZDY-SSW-SLH008,and XDB07020100)
文摘We synthesize a series of Mn substituted （Li, Fe）OHFeSe superconductor single crystals via a modified ion-exchange method, with the Mn concentration z （the atomic ratio of Mn：Se） ranging from 0 to 0.07. The distribution homogeneity of the Mn element incorporated into the lattice of （Li, Fe）OHFeSe is checked by combined measurements of high-angle- annular-dark-field （HAADF） imaging and electron energy-loss spectroscopy （EELS）. Interestingly, we find that the superconducting transition temperature Tc and unit cell parameter c of the Mn-doped （Li, Fe）OHFeSe samples display similar V-shaped evolutions with the increasing dopant concentration z. We propose that, with increasing doping level, the Mn dopant first occupies the tetrahedral sites in the （Li, Fe）OH layers before starting to substitute the Fe element in the su- perconducting FeSe layers, which accounts for the V-shaped change in cell parameter c. The observed positive correlation between the Tc and lattice parameter c, regardless of the Mn doping level z, indicates that a larger interlayer separation, or a weaker interlayer coupling, is essential for the high-Tc superconductivity in （Li, Fe）OHFeSe. This agrees with our previous observations on powder, single crystal, and film samples of （Li, Fe）OHFeSe superconductors.
基金supported by the National Natural Science Foundation of China (Grant No. 10975066)
文摘Mossbauer spectroscopy was used to probe the site-specific information of a K0.84Fe1.99Se2 superconductor. A spin excitation gap, △E≈5.5 meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field （HMF） at the iron site within the spin wave theory. Using the simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the alkali metal intercalated iron selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure.
基金supported by the National Key Basic Research Program of China(Grant No.2012CB921604)the National Natural Science Foundation of China(Grant Nos.11274069 and 11474064)
文摘We study numerically the phase diagram for s and d-wave fermionic superftuidity/superconductivity with spin-dependent band- width imbalance on a two-dimensional square-lattice. We also investigate the spontaneous space symmetry breaking states at low temperatures by solving the Bogoliubov-de Gennes equations. It is found that, the spatial configuration of the order parameter, both the uni-directional Fulde-Ferrell-Larkin-Ovchinnikov （FFLO） states and the two-dimensional FFLO state may show up in the presence of finite spin-dependent bandwidth imbalance. Moreover, we calculate the spectra of local density of states, and the experimental proposals of observing such FFLO states are therefore suggested.
