An Y-Ba-Cu-O superconducting film with onset temperature Tc(onset)=91K and zero resistance temperature Tc(end)=81.4K has been obtained for the first time by wing electron cyclotron resonance(ECR)plasma ions deposition...An Y-Ba-Cu-O superconducting film with onset temperature Tc(onset)=91K and zero resistance temperature Tc(end)=81.4K has been obtained for the first time by wing electron cyclotron resonance(ECR)plasma ions deposition technique.The relationship between the composition of the film and the atmosphere as well as the distance between the target and substrate has also been given.展开更多
As is well known, the relatively low critical current density J_c and the serious flux motion limit a variety of applications of high-temperature superconductors (HTSCs). The introduction
Electric transport and scanning tunneling spectrum(STS)have been investigated on polycrystalline samples of the new superconductor Bi4O4S3.A weak insulating behavior in the resistive curve has been induced in the norm...Electric transport and scanning tunneling spectrum(STS)have been investigated on polycrystalline samples of the new superconductor Bi4O4S3.A weak insulating behavior in the resistive curve has been induced in the normal state when the superconductivity is suppressed by applying a magnetic field.Interestingly,a kink appears on the temperature dependence of resistivity near 4 K at all high magnetic fields above 1 T when the bulk superconductivity is completely suppressed.This kink associated with the upper critical field as well as the wide range of excess conductance at low fields and high temperatures is explained as the possible evidence of strong superconducting fluctuation.From the tunneling spectra,a superconducting gap of about 3 meV is frequently observed yielding a ratio of 2Δ/kB TC^16.6.This value is much larger than the one predicted by the BCS theory in the weak coupling regime(2Δ/kB TC^3.53),which suggests the strong coupling superconductivity in the present system.Furthermore,the gapped feature persists on the spectra until 14 K in the STS measurement,which suggests a prominent fluctuation region of superconductivity.Such a superconducting fluctuation can survive at very high magnetic fields,which are far beyond the critical fields for bulk superconductivity as inferred both from electric transport and tunneling measurements.展开更多
The temperature and angle dependent resistivity of Ba(Fe 0.75 Ru 0.25) 2 As 2 single crystals were measured in magnetic fields up to 14 T.The temperature dependent resistivity with the magnetic field aligned parallel ...The temperature and angle dependent resistivity of Ba(Fe 0.75 Ru 0.25) 2 As 2 single crystals were measured in magnetic fields up to 14 T.The temperature dependent resistivity with the magnetic field aligned parallel to c-axis and ab-planes allow us to derive the slope of dH ab c2 /dT and dH c c2 /dT near T c yielding an anisotropy ratio Γ = dH ab c2 /dT/dH c c2 /dT ≈ 2.By scaling the curves of resistivity vs.angle measured at a fixed temperature but different magnetic fields within the framework of the anisotropic Ginzburg-Landau theory,we obtained the anisotropy in an alternative way.Again we found that the anisotropy(m c /m ab) 1/2 was close to 2.This value is similar to that in Ba0.6K0.4Fe2As2(K-doped Ba122) and Ba(Fe 0.92 Co 0.08) 2 As 2(Co-doped Ba122).This suggests that the 3D warping effect of the Fermi surface in Ru-doped samples may not be stronger than that in the K-doped or Co-doped Ba122 samples,therefore the possible nodes appearing in Ru-doped samples cannot be ascribed to the 3D warping effect of the Fermi surface.展开更多
Low-temperature specific heat was measured on the BaFe1.9Ni0.1As2 single crystals with critical transition temperature Tc = 20.1 K.A clear specific heat jump with the value ΔC/T|Tc ≈ 23 mJ/mol K2 was observed.In add...Low-temperature specific heat was measured on the BaFe1.9Ni0.1As2 single crystals with critical transition temperature Tc = 20.1 K.A clear specific heat jump with the value ΔC/T|Tc ≈ 23 mJ/mol K2 was observed.In addition,a roughly linear magnetic field dependence of the electronic specific heat coefficient Δγ(H) was found in the zero-temperature limit,suggesting that at least one Fermi pocket,probably the hole derivative one,was fully gapped with a small anisotropy in the present sample.A slight curvature of the curve Δγ(H) may suggest a complex gap structure(anisotropic gap or nodes) at other Fermi surfaces.展开更多
About two years have elapsed since the discovery of superconductivity at about26K in F-doped LaFeAsO.Within this short period,significant contributions have been achieved and the superconductivity temperature now reac...About two years have elapsed since the discovery of superconductivity at about26K in F-doped LaFeAsO.Within this short period,significant contributions have been achieved and the superconductivity temperature now reaches about57K.展开更多
Using self-flux method,we have successfully grown the parent phase of the single crystals of CaFeAsF1-x.The X-ray di?raction indicates good crystallinity.In-plane resistivity shows a bad metallic behavior with a sharp...Using self-flux method,we have successfully grown the parent phase of the single crystals of CaFeAsF1-x.The X-ray di?raction indicates good crystallinity.In-plane resistivity shows a bad metallic behavior with a sharp drop of resistivity at about T SDW=119K.This anomaly is associated with the possible spin density wave(SDW)order.Interestingly near T SDW,the resistivity exhibits a cusp-like feature,which may be understood as the strong coupling effect between the electrons and the antiferromagnetic(AF)spin fluctuations.A reduction of fluorine or application of a high pressure will suppress the SDW feature and induce superconductivity.Hall effect measurements reveal a positive Hall coefficient below T SDW indicating a dominant role of the hole-like charge carriers in the parent phase.Strong magnetoresistance has been observed below T SDW suggesting multiple conduction channels of the charge carriers.展开更多
Sr2VO3-δFeAs superconductors with different oxygen deficiencies have been successfully fabricated.It is found that the superconducting transition temperature drops down monotonically with the increase of nominal oxyg...Sr2VO3-δFeAs superconductors with different oxygen deficiencies have been successfully fabricated.It is found that the superconducting transition temperature drops down monotonically with the increase of nominal oxygen deficiency.The diminishing of superconductivity is accompanied by the enhancement of residual resistivity,indicating an anomalous scattering effect induced by the oxygen deficiency.The highest superconducting transition temperature at about 36 K is achieved near the stoichiometrical sample Sr2VO2.9FeAs.The Hall effect measurements reveal that the density of charge carriers(electron-like here) varies qualitatively with the increase of nominal oxygen deficiency.Magnetotransport measurements show that the superconducting transition changes from one-step-like shape at low fields to two-step-like one at high fields,indicating an enhanced vortex motion due to the high anisotropy.展开更多
基金This work was reported at the National HTS thin films conference,Hefei,April 1989.
文摘An Y-Ba-Cu-O superconducting film with onset temperature Tc(onset)=91K and zero resistance temperature Tc(end)=81.4K has been obtained for the first time by wing electron cyclotron resonance(ECR)plasma ions deposition technique.The relationship between the composition of the film and the atmosphere as well as the distance between the target and substrate has also been given.
文摘As is well known, the relatively low critical current density J_c and the serious flux motion limit a variety of applications of high-temperature superconductors (HTSCs). The introduction
基金supported by the 973 Project of the Ministry of Science and Technology of China (Grant Nos. 2011CBA001002, 2010CB923002, and 2012CB821403)the National Natural Science Foundation of China (Grant No. 11034011)+1 种基金the Program for New Century Excellent Talents in University (Grant No. NCET-12-0255)a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Electric transport and scanning tunneling spectrum(STS)have been investigated on polycrystalline samples of the new superconductor Bi4O4S3.A weak insulating behavior in the resistive curve has been induced in the normal state when the superconductivity is suppressed by applying a magnetic field.Interestingly,a kink appears on the temperature dependence of resistivity near 4 K at all high magnetic fields above 1 T when the bulk superconductivity is completely suppressed.This kink associated with the upper critical field as well as the wide range of excess conductance at low fields and high temperatures is explained as the possible evidence of strong superconducting fluctuation.From the tunneling spectra,a superconducting gap of about 3 meV is frequently observed yielding a ratio of 2Δ/kB TC^16.6.This value is much larger than the one predicted by the BCS theory in the weak coupling regime(2Δ/kB TC^3.53),which suggests the strong coupling superconductivity in the present system.Furthermore,the gapped feature persists on the spectra until 14 K in the STS measurement,which suggests a prominent fluctuation region of superconductivity.Such a superconducting fluctuation can survive at very high magnetic fields,which are far beyond the critical fields for bulk superconductivity as inferred both from electric transport and tunneling measurements.
基金supported by the National Natural Science Foundation of China (Grant No. 11034011/A0402)the National Basic Research Program of China (Grant Nos. 2011CBA00102 and 2012CB821403)PAPD
文摘The temperature and angle dependent resistivity of Ba(Fe 0.75 Ru 0.25) 2 As 2 single crystals were measured in magnetic fields up to 14 T.The temperature dependent resistivity with the magnetic field aligned parallel to c-axis and ab-planes allow us to derive the slope of dH ab c2 /dT and dH c c2 /dT near T c yielding an anisotropy ratio Γ = dH ab c2 /dT/dH c c2 /dT ≈ 2.By scaling the curves of resistivity vs.angle measured at a fixed temperature but different magnetic fields within the framework of the anisotropic Ginzburg-Landau theory,we obtained the anisotropy in an alternative way.Again we found that the anisotropy(m c /m ab) 1/2 was close to 2.This value is similar to that in Ba0.6K0.4Fe2As2(K-doped Ba122) and Ba(Fe 0.92 Co 0.08) 2 As 2(Co-doped Ba122).This suggests that the 3D warping effect of the Fermi surface in Ru-doped samples may not be stronger than that in the K-doped or Co-doped Ba122 samples,therefore the possible nodes appearing in Ru-doped samples cannot be ascribed to the 3D warping effect of the Fermi surface.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10221002/A0402 and 10774170/A0402)the National Basic Research Program of China (Grant Nos. 2006CB601000,2006CB921107,and 2006CB921802)the Chinese Academy of Sciences (ITSNEM)
文摘Low-temperature specific heat was measured on the BaFe1.9Ni0.1As2 single crystals with critical transition temperature Tc = 20.1 K.A clear specific heat jump with the value ΔC/T|Tc ≈ 23 mJ/mol K2 was observed.In addition,a roughly linear magnetic field dependence of the electronic specific heat coefficient Δγ(H) was found in the zero-temperature limit,suggesting that at least one Fermi pocket,probably the hole derivative one,was fully gapped with a small anisotropy in the present sample.A slight curvature of the curve Δγ(H) may suggest a complex gap structure(anisotropic gap or nodes) at other Fermi surfaces.
文摘About two years have elapsed since the discovery of superconductivity at about26K in F-doped LaFeAsO.Within this short period,significant contributions have been achieved and the superconductivity temperature now reaches about57K.
基金supported by the National Basic Research Program of China(Grant Nos.2011CBA00102,2010CB923002 and 2012CB821403)the National Natural Science Foundation of China and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Using self-flux method,we have successfully grown the parent phase of the single crystals of CaFeAsF1-x.The X-ray di?raction indicates good crystallinity.In-plane resistivity shows a bad metallic behavior with a sharp drop of resistivity at about T SDW=119K.This anomaly is associated with the possible spin density wave(SDW)order.Interestingly near T SDW,the resistivity exhibits a cusp-like feature,which may be understood as the strong coupling effect between the electrons and the antiferromagnetic(AF)spin fluctuations.A reduction of fluorine or application of a high pressure will suppress the SDW feature and induce superconductivity.Hall effect measurements reveal a positive Hall coefficient below T SDW indicating a dominant role of the hole-like charge carriers in the parent phase.Strong magnetoresistance has been observed below T SDW suggesting multiple conduction channels of the charge carriers.
基金supported by the National Natural Science Foundation of China,the National Basic Research Program of China (Grant Nos. 2006CB601000 and 2006CB921802)the Chinese Academy of Sciences Project (Grant No. ITSNEM)
文摘Sr2VO3-δFeAs superconductors with different oxygen deficiencies have been successfully fabricated.It is found that the superconducting transition temperature drops down monotonically with the increase of nominal oxygen deficiency.The diminishing of superconductivity is accompanied by the enhancement of residual resistivity,indicating an anomalous scattering effect induced by the oxygen deficiency.The highest superconducting transition temperature at about 36 K is achieved near the stoichiometrical sample Sr2VO2.9FeAs.The Hall effect measurements reveal that the density of charge carriers(electron-like here) varies qualitatively with the increase of nominal oxygen deficiency.Magnetotransport measurements show that the superconducting transition changes from one-step-like shape at low fields to two-step-like one at high fields,indicating an enhanced vortex motion due to the high anisotropy.
