We report superconductivity in a new ternary molybdenum pnictide Rb2 Mo3 As3,synthesized via the solid state reaction method.Powder x-ray diffraction analysis reveals a hexagonal crystal structure with space group P6 ...We report superconductivity in a new ternary molybdenum pnictide Rb2 Mo3 As3,synthesized via the solid state reaction method.Powder x-ray diffraction analysis reveals a hexagonal crystal structure with space group P6 m2(No.187),and the refined lattice parameters are a=10.431(5)A,c=4.460(4)A.SEM images show rod-like grains with good ductility,confirming a quasi-one-dimensional(Q1 D)structure.Electrical resistivity and dc magnetic susceptibility characterizations exhibit superconductivity with an onset of Tc=10.5 K.The upper critical field of Rb2 Mo3 As3 is estimated to be 28.2 T at zero temperature,providing an evidence of possible unconventional superconductivity.Our recent discovery of MoAs-based superconductors above 10 K provides a unique platform for the study of exotic superconductivity in 4 d electron systems with Q1 D crystal structures.展开更多
In the iron-based high-To bulk superconductors, Tc above 50 K was only observed in the electron-doped 1111-type compounds. Here we revisit the electron-doped SmFeAsO polycrystals to make a further investigation for th...In the iron-based high-To bulk superconductors, Tc above 50 K was only observed in the electron-doped 1111-type compounds. Here we revisit the electron-doped SmFeAsO polycrystals to make a further investigation for the highest Tc in these materials. To introduce more electron carriers and less crystal lattice distortions, we study the Th and F eodoping effects into the Sm-O layers with heavy electron doping. Dozens of Sm1-xThx FeAsO1-yFy samples are synthesized through the solid state reaction method, and these samples are carefully characterized by the structural, resistive, and magnetic measurements. We find that the codoping of Th and F clearly enhances the superconducting Tc more than the Th or F single-doped samples, with the highest record Tc up to 58.6K when x = 0.2 and y=0.225. Further element doping causes more impurities and lattice distortions in the samples with a weakened superconductivity.展开更多
The(Ca,R)FeAs_(2)(R=La,Pr,etc.)superconductors with a signature of superconductivity transition above 40 K possess a new kind of block layers that consist of zig-zag As chains.We report the electronic structure of the...The(Ca,R)FeAs_(2)(R=La,Pr,etc.)superconductors with a signature of superconductivity transition above 40 K possess a new kind of block layers that consist of zig-zag As chains.We report the electronic structure of the new(Ca,La)FeAs_(2)superconductor investigated by both band structure calculations and high resolution angle-resolved photoemission spectroscopy measurements.Band structure calculations indicate that there are four hole-like bands around the zone centerΓ(0,0)and two electron-like bands near the zone corner M(π,π)in CaFeAs_(2).In our angle-resolved photoemission measurements on(Ca0.9La0.1)FeAs_(2),we have observed three hole-like bands around theΓpoint and one electron-like Fermi surface near the M(π,π)point.These results provide important information to compare and contrast with the electronic structure of other iron-based compounds in understanding the superconductivity mechanism in the iron-based superconductors.展开更多
Single crystals of undoped CaFe2As2 are grown by an FeAs self-flux method, and the crystals are quenched in ice-water rapidly after high-temperature growth. The quenched crystal undergoes a collapsed tetragonal struct...Single crystals of undoped CaFe2As2 are grown by an FeAs self-flux method, and the crystals are quenched in ice-water rapidly after high-temperature growth. The quenched crystal undergoes a collapsed tetragonal structural phase transition around 80 K revealed by the temperature-dependent x-ray diffraction measurements. Superconductivity below 25 K is observed in the collapsed phase by resistivity and magnetization measurements. The isothermal magnetization curve measured at 2 K indicates that this is a typical type-ll superconductor. For comparison, we systematically characterize the properties of the furnace-cooled, quenched, and post-annealed single crystals, and find strong internal crystallographic strain existing in the quenched samples, which is the key for the occurrence of superconductivity in the undoped CaFe2As2 single crystals.展开更多
In this article,the Sm-doping single crystals Ca1-xSmxFe2As2（x = 0 0.2） were prepared by the Ca As flux method,and followed by a rapid quenching treatment after the high temperature growth.The samples were character...In this article,the Sm-doping single crystals Ca1-xSmxFe2As2（x = 0 0.2） were prepared by the Ca As flux method,and followed by a rapid quenching treatment after the high temperature growth.The samples were characterized by structural,resistive,and magnetic measurements.The successful Sm-substitution was revealed by the reduction of the lattice parameter c,due to the smaller ionic radius of Sm3＋than Ca2＋.Superconductivity was observed in all samples with onset Tc varying from 27 K to 44 K upon Sm-doping.The coexistence of a collapsed phase transition and the superconducting transition was found for the lower Sm-doping samples.Zero resistivity and substantial superconducting volume fraction only happen in higher Sm-doping crystals with the nominal x 〉 0.10.The doping dependences of the c-axis length and onset Tc were summarized.The high-Tc observed in these quenched crystals may be attributed to simultaneous tuning of electron carriers doping and strain effect caused by lattice reduction of Sm-substitution.展开更多
基金Supported by the National Key Research and Development of China(Grant Nos.2018YFA0704200 and 2016YFA0300301)the National Natural Science Foundation of China(Grant No.11774402)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)。
文摘We report superconductivity in a new ternary molybdenum pnictide Rb2 Mo3 As3,synthesized via the solid state reaction method.Powder x-ray diffraction analysis reveals a hexagonal crystal structure with space group P6 m2(No.187),and the refined lattice parameters are a=10.431(5)A,c=4.460(4)A.SEM images show rod-like grains with good ductility,confirming a quasi-one-dimensional(Q1 D)structure.Electrical resistivity and dc magnetic susceptibility characterizations exhibit superconductivity with an onset of Tc=10.5 K.The upper critical field of Rb2 Mo3 As3 is estimated to be 28.2 T at zero temperature,providing an evidence of possible unconventional superconductivity.Our recent discovery of MoAs-based superconductors above 10 K provides a unique platform for the study of exotic superconductivity in 4 d electron systems with Q1 D crystal structures.
基金Supported by the National Natural Science Foundation of China under Grant No 11474339the National Basic Research Program of China under Grant No 2016YFA0300301the Youth Innovation Promotion Association of the Chinese Academy of Sciences
文摘In the iron-based high-To bulk superconductors, Tc above 50 K was only observed in the electron-doped 1111-type compounds. Here we revisit the electron-doped SmFeAsO polycrystals to make a further investigation for the highest Tc in these materials. To introduce more electron carriers and less crystal lattice distortions, we study the Th and F eodoping effects into the Sm-O layers with heavy electron doping. Dozens of Sm1-xThx FeAsO1-yFy samples are synthesized through the solid state reaction method, and these samples are carefully characterized by the structural, resistive, and magnetic measurements. We find that the codoping of Th and F clearly enhances the superconducting Tc more than the Th or F single-doped samples, with the highest record Tc up to 58.6K when x = 0.2 and y=0.225. Further element doping causes more impurities and lattice distortions in the samples with a weakened superconductivity.
基金Supported by the National Natural Science Foundation of China under Grant No 10734120the National Basic Research Program of China under Grant Nos 2011CB921703 and 2011CB605903.
文摘The(Ca,R)FeAs_(2)(R=La,Pr,etc.)superconductors with a signature of superconductivity transition above 40 K possess a new kind of block layers that consist of zig-zag As chains.We report the electronic structure of the new(Ca,La)FeAs_(2)superconductor investigated by both band structure calculations and high resolution angle-resolved photoemission spectroscopy measurements.Band structure calculations indicate that there are four hole-like bands around the zone centerΓ(0,0)and two electron-like bands near the zone corner M(π,π)in CaFeAs_(2).In our angle-resolved photoemission measurements on(Ca0.9La0.1)FeAs_(2),we have observed three hole-like bands around theΓpoint and one electron-like Fermi surface near the M(π,π)point.These results provide important information to compare and contrast with the electronic structure of other iron-based compounds in understanding the superconductivity mechanism in the iron-based superconductors.
基金Supported by the National Natural Science Foundation of China under Grant No 11474339the National Basic Research Program of China under Grant Nos 2010CB923000 and 2011CBA00100the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No XDB07020100
文摘Single crystals of undoped CaFe2As2 are grown by an FeAs self-flux method, and the crystals are quenched in ice-water rapidly after high-temperature growth. The quenched crystal undergoes a collapsed tetragonal structural phase transition around 80 K revealed by the temperature-dependent x-ray diffraction measurements. Superconductivity below 25 K is observed in the collapsed phase by resistivity and magnetization measurements. The isothermal magnetization curve measured at 2 K indicates that this is a typical type-ll superconductor. For comparison, we systematically characterize the properties of the furnace-cooled, quenched, and post-annealed single crystals, and find strong internal crystallographic strain existing in the quenched samples, which is the key for the occurrence of superconductivity in the undoped CaFe2As2 single crystals.
基金Project supported by the National Natural Science Foundation of China(Grant No.11474339)the National Basic Research Program of China(Grant Nos.2010CB923000 and 2011CBA00100)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB07020100)
文摘In this article,the Sm-doping single crystals Ca1-xSmxFe2As2（x = 0 0.2） were prepared by the Ca As flux method,and followed by a rapid quenching treatment after the high temperature growth.The samples were characterized by structural,resistive,and magnetic measurements.The successful Sm-substitution was revealed by the reduction of the lattice parameter c,due to the smaller ionic radius of Sm3＋than Ca2＋.Superconductivity was observed in all samples with onset Tc varying from 27 K to 44 K upon Sm-doping.The coexistence of a collapsed phase transition and the superconducting transition was found for the lower Sm-doping samples.Zero resistivity and substantial superconducting volume fraction only happen in higher Sm-doping crystals with the nominal x 〉 0.10.The doping dependences of the c-axis length and onset Tc were summarized.The high-Tc observed in these quenched crystals may be attributed to simultaneous tuning of electron carriers doping and strain effect caused by lattice reduction of Sm-substitution.
