We investigate the vortex dynamics in two typical hole doped iron based superconductors CaKFe_4As_4(CaK1144) and Ba_(0.6)K_(0.4)Fe_2As_2(BaK122) with similar superconducting transition temperatures. It is found that t...We investigate the vortex dynamics in two typical hole doped iron based superconductors CaKFe_4As_4(CaK1144) and Ba_(0.6)K_(0.4)Fe_2As_2(BaK122) with similar superconducting transition temperatures. It is found that the magnetization hysteresis loop exhibits a clear second peak effect in BaK122 in wide temperature region while it is absent in CaK1144. However, a second peak effect of critical current density versus temperature is observed in CaK1144, which is however absent in BaK122. The different behaviors of second peak effect in BaK122 and CaK1144 may suggest distinct origins of vortex pinning in different systems. Magnetization and its relaxation have also been measured by using dynamical and conventional relaxation methods for both systems. Analysis and comparison of the two distinct systems show that the vortex pinning is stronger and the critical current density is higher in BaK122 system. It is found that the Maley's method can be used and thus the activation energy can be determined in BaK122 by using the time dependent magnetization in wide temperature region, but this is not applicable in CaK1144 system.Finally we present the different regimes with distinct vortex dynamics in the field-temperature diagram for the two systems.展开更多
Low-temperature specific heat(SH)is measured for the 12442-type KCa2Fe4As4F2 single crystal under different magnetic fields.A clear SH jump with the height of?C/T|Tc=130 mJ mol-1 K-2 is observed at the superconducting...Low-temperature specific heat(SH)is measured for the 12442-type KCa2Fe4As4F2 single crystal under different magnetic fields.A clear SH jump with the height of?C/T|Tc=130 mJ mol-1 K-2 is observed at the superconducting transition temperature Tc.It is found that the electronic SH coefficient?γ(H)quickly increases when the field is in the low-field region below 3T and then considerably slows down the increase with a further increase in the field,which indicates a rather strong anisotropy or multi-gap feature with a small minimum in the superconducting gap(s).The temperature-dependent SH data indicate the presence of the T2 term,which supplies further information and supports the picture with a line-nodal gap structure.Moreover,the onset point of the SH transition remains almost unchanged under the field as high as 9 T,which is similar to that observed in cuprates,and places this system in the middle between the BCS limit and the Bose-Einstein condensation.展开更多
A new kind of catalyst WOBr_4,which can be used in the polymerization of phenylacetylene(PhA),has been synthesized.The obtained polyphenylcetylene(PPhA) using WOBr_4 as catalyst is soluble、fusible、with brown-red col...A new kind of catalyst WOBr_4,which can be used in the polymerization of phenylacetylene(PhA),has been synthesized.The obtained polyphenylcetylene(PPhA) using WOBr_4 as catalyst is soluble、fusible、with brown-red colour and has 1831(M n).The analysis of the stucture of PPhA shows that the polymer has cis-transoidal structure,therefore,the reaction mechanism is via complex catalysis.展开更多
基金supported by the National Key Research and Development Program of China(2016YFA0300401)the National Natural Science Foundation of China(A0402/11534005)
文摘We investigate the vortex dynamics in two typical hole doped iron based superconductors CaKFe_4As_4(CaK1144) and Ba_(0.6)K_(0.4)Fe_2As_2(BaK122) with similar superconducting transition temperatures. It is found that the magnetization hysteresis loop exhibits a clear second peak effect in BaK122 in wide temperature region while it is absent in CaK1144. However, a second peak effect of critical current density versus temperature is observed in CaK1144, which is however absent in BaK122. The different behaviors of second peak effect in BaK122 and CaK1144 may suggest distinct origins of vortex pinning in different systems. Magnetization and its relaxation have also been measured by using dynamical and conventional relaxation methods for both systems. Analysis and comparison of the two distinct systems show that the vortex pinning is stronger and the critical current density is higher in BaK122 system. It is found that the Maley's method can be used and thus the activation energy can be determined in BaK122 by using the time dependent magnetization in wide temperature region, but this is not applicable in CaK1144 system.Finally we present the different regimes with distinct vortex dynamics in the field-temperature diagram for the two systems.
基金the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.2015187)the National Natural Science Foundation of China(Grant Nos.11204338,and 11927807)the“Strategic Priority Research Program(B)”of the Chinese Academy of Sciences(Grant No.XDB04040300).Wei Li also acknowledges the start-up funding from Fudan University.
文摘Low-temperature specific heat(SH)is measured for the 12442-type KCa2Fe4As4F2 single crystal under different magnetic fields.A clear SH jump with the height of?C/T|Tc=130 mJ mol-1 K-2 is observed at the superconducting transition temperature Tc.It is found that the electronic SH coefficient?γ(H)quickly increases when the field is in the low-field region below 3T and then considerably slows down the increase with a further increase in the field,which indicates a rather strong anisotropy or multi-gap feature with a small minimum in the superconducting gap(s).The temperature-dependent SH data indicate the presence of the T2 term,which supplies further information and supports the picture with a line-nodal gap structure.Moreover,the onset point of the SH transition remains almost unchanged under the field as high as 9 T,which is similar to that observed in cuprates,and places this system in the middle between the BCS limit and the Bose-Einstein condensation.
文摘A new kind of catalyst WOBr_4,which can be used in the polymerization of phenylacetylene(PhA),has been synthesized.The obtained polyphenylcetylene(PPhA) using WOBr_4 as catalyst is soluble、fusible、with brown-red colour and has 1831(M n).The analysis of the stucture of PPhA shows that the polymer has cis-transoidal structure,therefore,the reaction mechanism is via complex catalysis.
