Mesa-structured submicron intrinsic Josephson junctions are successfully fabricated and well characterized on underdoped Bi2Sr2Ca1-xYxCu2O8＋δ single crystals with a Tc of 80 K. Tunneling spectra at the temperatures ...Mesa-structured submicron intrinsic Josephson junctions are successfully fabricated and well characterized on underdoped Bi2Sr2Ca1-xYxCu2O8＋δ single crystals with a Tc of 80 K. Tunneling spectra at the temperatures ranging from 4.2 K to 295 K are measured. A pulse technique is used to reduce sample heating for the measurement near pseudogap opening temperature T^＊ - 280 K. Our experimental results show that the superconducting gap, the peakdip separation, and the pseudogap opening temperature are all increased as compared with those from near optimally doped samples, which requires further theoretical analysis in the future.展开更多
The growth of crystals of the high T c oxide superconductors has been hampe red by the complexities of the materials and their phase diagrams.The most common crys tal growth technique adopted for these oxides is the ...The growth of crystals of the high T c oxide superconductors has been hampe red by the complexities of the materials and their phase diagrams.The most common crys tal growth technique adopted for these oxides is the “flux”method,where the st arting materials are solved in a melt,which is usually formed by excess CuO and BaO or a KCl/NaCl mixture.The crystals are produced by slow cooling of the heate d solvent.This method,however,suffers from several disadvantages: (1) the crystals are contaminated with the crucible material, (2) the crystals are difficult to remove from the crucible, (3) the crystals contain flux inclusions.展开更多
Since Bi2Sr2Ca1Cu2O8＋x（Bi2212） wires are subject to mechanical loadings, degradation of critical current will occur. The effect of compressive loadings on the critical current of Bi2212 wire is studied by consideri...Since Bi2Sr2Ca1Cu2O8＋x（Bi2212） wires are subject to mechanical loadings, degradation of critical current will occur. The effect of compressive loadings on the critical current of Bi2212 wire is studied by considering micro-buckling of filament. A Bi2212 wire is regarded as a unidirectional filament-reinforced composite in the theoretical analysis. By considering the influence of inclusion, the micro-buckling wavelength can be derived by using a two-dimensional model. Based on the experimental results, the critical current is fitted as a function of buckling wavelength. It is found that the decrease of the critical current is directly proportional to the reciprocal of square of the buckling wavelength. Change of micro-buckling wavelength with material parameters is discussed. A critical strain in the wire with a filament bridge is analyzed using the finite element method.展开更多
The effect of Y substitution for Ca on the crystal structure and electronic states of Bi_2Sr_2CaCu_2O_(8+y) was studied. It is found that the modulation period of the incommensurate superlattice along b axis decreases...The effect of Y substitution for Ca on the crystal structure and electronic states of Bi_2Sr_2CaCu_2O_(8+y) was studied. It is found that the modulation period of the incommensurate superlattice along b axis decreases from 4.7b to about 4.0b gradually, which implies the change of the extra oxygen atoms residing within double Bi-O layers. Two kinds of modulation structures with periods of 4b and 8b exist in the same compound as Ca is completely substituted by Y. XPS was employed to study the change in the electronic structure. The results suggest that the variation of superconductivity is not caused by the slight change in crystal structure, but rather by the hole filling in O2p orbitals in CuO_2 layers. For this substituted system, it is still the case where one hole in Cu3d orbital (3d^9) is corresponding to the strong correlation antiferromaguetic insulator, and an extra hole in O2p orbital in CuO_2 layer (3d^9L) to the superconductor.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.10974242)
文摘Mesa-structured submicron intrinsic Josephson junctions are successfully fabricated and well characterized on underdoped Bi2Sr2Ca1-xYxCu2O8＋δ single crystals with a Tc of 80 K. Tunneling spectra at the temperatures ranging from 4.2 K to 295 K are measured. A pulse technique is used to reduce sample heating for the measurement near pseudogap opening temperature T^＊ - 280 K. Our experimental results show that the superconducting gap, the peakdip separation, and the pseudogap opening temperature are all increased as compared with those from near optimally doped samples, which requires further theoretical analysis in the future.
文摘The growth of crystals of the high T c oxide superconductors has been hampe red by the complexities of the materials and their phase diagrams.The most common crys tal growth technique adopted for these oxides is the “flux”method,where the st arting materials are solved in a melt,which is usually formed by excess CuO and BaO or a KCl/NaCl mixture.The crystals are produced by slow cooling of the heate d solvent.This method,however,suffers from several disadvantages: (1) the crystals are contaminated with the crucible material, (2) the crystals are difficult to remove from the crucible, (3) the crystals contain flux inclusions.
基金Project supported by the National Natural Science Foundation of China(Nos.11327802,11472120,and 11421062)the National Key Project of Magneto-Constrained Fusion Energy Development Program(No.2013GB110002)the Fundamental Research Funds for the Central Universities(No.lzujbky-2017-k18)
文摘Since Bi2Sr2Ca1Cu2O8＋x（Bi2212） wires are subject to mechanical loadings, degradation of critical current will occur. The effect of compressive loadings on the critical current of Bi2212 wire is studied by considering micro-buckling of filament. A Bi2212 wire is regarded as a unidirectional filament-reinforced composite in the theoretical analysis. By considering the influence of inclusion, the micro-buckling wavelength can be derived by using a two-dimensional model. Based on the experimental results, the critical current is fitted as a function of buckling wavelength. It is found that the decrease of the critical current is directly proportional to the reciprocal of square of the buckling wavelength. Change of micro-buckling wavelength with material parameters is discussed. A critical strain in the wire with a filament bridge is analyzed using the finite element method.
基金Project supported by the National Natural Science Foundation of China and by the Laboratory of Structure and Element Analysis, Academia Sinica
文摘The effect of Y substitution for Ca on the crystal structure and electronic states of Bi_2Sr_2CaCu_2O_(8+y) was studied. It is found that the modulation period of the incommensurate superlattice along b axis decreases from 4.7b to about 4.0b gradually, which implies the change of the extra oxygen atoms residing within double Bi-O layers. Two kinds of modulation structures with periods of 4b and 8b exist in the same compound as Ca is completely substituted by Y. XPS was employed to study the change in the electronic structure. The results suggest that the variation of superconductivity is not caused by the slight change in crystal structure, but rather by the hole filling in O2p orbitals in CuO_2 layers. For this substituted system, it is still the case where one hole in Cu3d orbital (3d^9) is corresponding to the strong correlation antiferromaguetic insulator, and an extra hole in O2p orbital in CuO_2 layer (3d^9L) to the superconductor.
