Combining in-depth neutron diffraction and systematic bulk studies,we discover that the√5×√5 Fe vacancy order,with its associated block antiferromagnetic order,is the ground state with varying occupancy ratios ...Combining in-depth neutron diffraction and systematic bulk studies,we discover that the√5×√5 Fe vacancy order,with its associated block antiferromagnetic order,is the ground state with varying occupancy ratios of the iron 16i and vacancy 4d sites across the phase-diagram of K_(x)Fe_(2)-ySe_(2).The orthorhombic order,with one of the four Fe sites vacant,appears only at intermediate temperatures as a competing phase.The material experiences an insulator to metal crossover when the√5×√5 order is highly developed.Superconductivity occurs in such a metallic phase.展开更多
The specific heat of the recently discovered superconductor MgB_(2) has been measured at temperatures ranging from 4.5 to 80 K.Superconducting anomalyΔC at Tc is clearly observed.The total specific heat in normal sta...The specific heat of the recently discovered superconductor MgB_(2) has been measured at temperatures ranging from 4.5 to 80 K.Superconducting anomalyΔC at Tc is clearly observed.The total specific heat in normal state can be well fitted by electronic and phonon contributions.The Debye temperatureθD is obtained to be 737 K,much larger than other intermetallic superconductors.Normal state electronic specific heat coefficientγis found to be 2.48±0.5 mJ/mol.K^(2) andΔC/γTc is between 1.41 and 2.15.展开更多
Specific heat in applied magnetic fields were measured to a low temperature 0.08 K and resistance to 0.5K.The specific heat shows a wide peak at 1 K,and a high value of the electronic coefficientγ(T→0)1200 mJ/mol...Specific heat in applied magnetic fields were measured to a low temperature 0.08 K and resistance to 0.5K.The specific heat shows a wide peak at 1 K,and a high value of the electronic coefficientγ(T→0)1200 mJ/mol·K^(2) is obtained.The temperature independence of the wide peak in specific heat at 1K in magnetic fields further suggests that the high valueγof CeCuGa is due to Kondo effect.展开更多
High quality single crystal CaFe4As3 was grown by using the Sn flux method. Unlike layered CaFe2As2, CaFe4As3 crystallizes in an orthorhombic three-dimensional structure. Two magnetic ordering transitions are observed...High quality single crystal CaFe4As3 was grown by using the Sn flux method. Unlike layered CaFe2As2, CaFe4As3 crystallizes in an orthorhombic three-dimensional structure. Two magnetic ordering transitions are observed at - 90 K and - 27 K, respectively. The high temperature transition is an antiferromagnetic（AF） ordering transition. However, the low temperature transition shows complex properties. It shows a ferromagnetic-like transition when a field is applied along b-axis, while antiferromagnetism-like transition when a field is applied perpendicular to b-axis. These results suggest that the low temperature transition at 27 K is a first-order transition from an AF state to a canted AF state. In addition, the low temperature electron specific heat coefficient reaches as high as 143 mJ/mol.K2, showing a heavy fermion behavior.展开更多
^(75)As nuclear magnetic resonance(NMR)was measured for Ba(Fe_(1-x)Ni_(x))_(2)As_(2)single crystals with x=0.05 and x=0.1 under 0 and 1.5GPa,respectively.For the optimal doped sample with x=0.05,the superconducting tr...^(75)As nuclear magnetic resonance(NMR)was measured for Ba(Fe_(1-x)Ni_(x))_(2)As_(2)single crystals with x=0.05 and x=0.1 under 0 and 1.5GPa,respectively.For the optimal doped sample with x=0.05,the superconducting transition temperature,Tc,is strongly suppressed from 18 to 5 K,while for the over-doped sample with x=0.1,it is turned from a superconducting ground state to a disordered paramagnetic state under 1.5 GPa.Our experimental results show that the antiferromagnetic spin fluctuations,as well as Tc,are suppressed.The experimental results can be explained with the two-band model.As a result,the electronic band is shifted downwards with an increase in pressure,and the electrons become the dominant carriers in the system.展开更多
基金Supported by the National Basic Research Program of China under Grant Nos 2012CB921700,2011CBA00112,2011CBA00103 and 2009CB929104National Natural Science Foundation of China under Grant Nos 11034012,11190024,10974175 and 10934005.
文摘Combining in-depth neutron diffraction and systematic bulk studies,we discover that the√5×√5 Fe vacancy order,with its associated block antiferromagnetic order,is the ground state with varying occupancy ratios of the iron 16i and vacancy 4d sites across the phase-diagram of K_(x)Fe_(2)-ySe_(2).The orthorhombic order,with one of the four Fe sites vacant,appears only at intermediate temperatures as a competing phase.The material experiences an insulator to metal crossover when the√5×√5 order is highly developed.Superconductivity occurs in such a metallic phase.
基金Supported by the National Natural Science Foundation of China under Grant No.19825111.
文摘The specific heat of the recently discovered superconductor MgB_(2) has been measured at temperatures ranging from 4.5 to 80 K.Superconducting anomalyΔC at Tc is clearly observed.The total specific heat in normal state can be well fitted by electronic and phonon contributions.The Debye temperatureθD is obtained to be 737 K,much larger than other intermetallic superconductors.Normal state electronic specific heat coefficientγis found to be 2.48±0.5 mJ/mol.K^(2) andΔC/γTc is between 1.41 and 2.15.
基金Supported by the National Natural Science Foundation of China under Grant No.19274049National Commission of Science and Technology。
文摘Specific heat in applied magnetic fields were measured to a low temperature 0.08 K and resistance to 0.5K.The specific heat shows a wide peak at 1 K,and a high value of the electronic coefficientγ(T→0)1200 mJ/mol·K^(2) is obtained.The temperature independence of the wide peak in specific heat at 1K in magnetic fields further suggests that the high valueγof CeCuGa is due to Kondo effect.
基金Project supported by the National Natural Science Foundation of China(Grant No.Y1JA011x11)
文摘High quality single crystal CaFe4As3 was grown by using the Sn flux method. Unlike layered CaFe2As2, CaFe4As3 crystallizes in an orthorhombic three-dimensional structure. Two magnetic ordering transitions are observed at - 90 K and - 27 K, respectively. The high temperature transition is an antiferromagnetic（AF） ordering transition. However, the low temperature transition shows complex properties. It shows a ferromagnetic-like transition when a field is applied along b-axis, while antiferromagnetism-like transition when a field is applied perpendicular to b-axis. These results suggest that the low temperature transition at 27 K is a first-order transition from an AF state to a canted AF state. In addition, the low temperature electron specific heat coefficient reaches as high as 143 mJ/mol.K2, showing a heavy fermion behavior.
基金Supported by the National Basic Research Program of China under Grant No 2011CB921701the National Natural Science Foundation of China under Grant No 11015422the Knowledge Innovation Program of the Chinese Academy of Sciences under Grant No KJCX2-EW-W11.
文摘^(75)As nuclear magnetic resonance(NMR)was measured for Ba(Fe_(1-x)Ni_(x))_(2)As_(2)single crystals with x=0.05 and x=0.1 under 0 and 1.5GPa,respectively.For the optimal doped sample with x=0.05,the superconducting transition temperature,Tc,is strongly suppressed from 18 to 5 K,while for the over-doped sample with x=0.1,it is turned from a superconducting ground state to a disordered paramagnetic state under 1.5 GPa.Our experimental results show that the antiferromagnetic spin fluctuations,as well as Tc,are suppressed.The experimental results can be explained with the two-band model.As a result,the electronic band is shifted downwards with an increase in pressure,and the electrons become the dominant carriers in the system.
