We report systematic studies on superconducting properties of the Laves phase superconductor ZrIr_(2).It crystallizes in a C15-type(cubic MgCu_(2)-type,space group Fd3m)structure in which the Ir atoms form a kagome la...We report systematic studies on superconducting properties of the Laves phase superconductor ZrIr_(2).It crystallizes in a C15-type(cubic MgCu_(2)-type,space group Fd3m)structure in which the Ir atoms form a kagome lattice,with cell parameters a=b=c=7.3596(1)?.Resistivity and magnetic susceptibility measurements indicate that ZrIr_(2) is a type-Ⅱsuperconductor with a transition temperature of 4.0 K.The estimated lower and upper critical fields are 12.8 mT and 4.78 T,respectively.Heat capacity measurements confirm the bulk superconductivity in ZrIr_(2).ZrIr_(2) is found to possibly host strong-coupled s-wave superconductivity with the normalized specific heat change△C_(e)/γT_(c)~1.86 and the coupling strength△_(0)/k_BT_(c)~1.92.First-principles calculations suggest that ZrIr_(2) has three-dimensional Fermi surfaces with simple topologies,and the states at Fermi level mainly originate from the Ir-5d and Zr-4d orbitals.Similar to SrIr_(2) and ThIr_(2),spin–orbit coupling has dramatic influences on the band structure in ZrIr_(2).展开更多
We report a comprehensive study on a layered-structure compound of NaZn_(4)As_(3),which has been predicted to be an ideal topological semimetal(TSM) candidate.It is found that NaZn_(4)As_(3) undergoes a structural tra...We report a comprehensive study on a layered-structure compound of NaZn_(4)As_(3),which has been predicted to be an ideal topological semimetal(TSM) candidate.It is found that NaZn_(4)As_(3) undergoes a structural transformation from high temperature rhombohedral to a low temperature monoclinic phase.The electric resistivity exhibits a metal-to-insulatorlike transition at around 100 K,and then develops a plateau at low temperature,which might be related to the protected topologically conducting surface states.Our first-principles calculation confirms further that NaZn_(4)As_(3) is a topological insulator(TI) for both different phases rather than a previously proposed TSM.The Hall resistivity reveals that the hole carriers dominate the transport properties for the whole temperature range investigated.Furthermore,an obvious kink possibly associated to the structure transition has been detected in thermopower around ~ 170 K.The large thermopower and moderate κ indicate that NaZn_(4)As_(3) and/or its derivatives can provide a good platform for optimizing and studying the thermoelectric performance.展开更多
We report the synthesis,crystal structure,and superconductivity of Ti_(4)Ir_(2)O.The title compound crystallizes in an η-carbide type structure of the space group Fd3m(No.227),with lattice parameters a=b=c=11.6194(1)...We report the synthesis,crystal structure,and superconductivity of Ti_(4)Ir_(2)O.The title compound crystallizes in an η-carbide type structure of the space group Fd3m(No.227),with lattice parameters a=b=c=11.6194(1)A.The superconducting temperature T_(c) is found to be 5.1-5.7 K.Most surprisingly,Ti_(4)Ir_(2)O hosts an upper critical field of 16.45 T,which is far beyond the Pauli paramagnetic limit.Strong coupled superconductivity with evidences for multigap is revealed by the measurements of heat capacity and upper critical field.First-principles calculations suggest that the density of states near the Fermi level originates from the hybridization of Ti-3d and Ir-5d orbitals,and the effect of spin-orbit coupling on the Fermi surfaces is prominent.Large values of the Wilson ratio(R_(W)∼3.9),the Kadowaki-Woods ratio[A/γ^(2)∼9.0×10^(−6)µΩ·cm/(mJ·mol^(−1)·K^(−1))^(2)],and the Sommerfeld coefficient(γ=33.74 mJ·mol^(−1)·K^(−2))all suggest strong electron correlations(similar to heavy fermion systems)in Ti_(4)Ir_(2)O.The violation of Pauli limit is possibly due to a combination of strong-coupled superconductivity and large spin-orbit scattering.With these intriguing behaviors,Ti_(4)Ir_(2)O serves as a candidate for unconventional superconductor.展开更多
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
We report a direct microwave synthesis method for the preparation of 11-type high quality Fe(Te,Se) polycrystalline superconductors. The bulk samples are rapidly synthesized under the microwave irradiation during seve...We report a direct microwave synthesis method for the preparation of 11-type high quality Fe(Te,Se) polycrystalline superconductors. The bulk samples are rapidly synthesized under the microwave irradiation during several minutes, with a subsequent annealing process at 400℃. The samples exhibit a nearly single phase of the tetragonal PbO-type crystal structure with minor impurities. Morphology characterization shows high density, tight grain connectivity and large grain sizes around 100 μm with small cavities inside the sample. Resistivity and magnetization measurements both show similar superconducting transitions above 14 K. The magnetic hysteresis measurements display broad and symmetric loops without magnetic background, and a high critical current density J_c about 1.2 × 10~4 A/cm^2 at 2 K and 7 T is estimated by the Bean model. Compared with the solidstate reaction synthesized samples, these superconducting bulks from microwave-assisted synthesis are possibly free of the interstitial Fe due to smaller c-axis, higher T_c in magnetic transitions, better M–H loops without magnetic background and greatly enhanced J_c, and are promising as raw materials for the non-toxic Fe-based superconducting wires for large currents and high field applications.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
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
We report the microwave synthesis and the doping effect of Mo_(3-)xRe_xAl_(2)C(0≤x≤0.3)superconductor.Re doping into Mo_(3)Al_(2)C results in a regular shrinkage of the lattice,marked by the linear decrease of latti...We report the microwave synthesis and the doping effect of Mo_(3-)xRe_xAl_(2)C(0≤x≤0.3)superconductor.Re doping into Mo_(3)Al_(2)C results in a regular shrinkage of the lattice,marked by the linear decrease of lattice parameter a from6.868(1)A(for Mo_(3)Al_(2)C)to 6.846(2)A(for Mo_(2.7)Re_(0.3)Al_(2)C).Upon Re doping,T_(c)of Mo_(3-x)Re_xAl_(2)C first increases and then decreases,with the maximum T_(c)=9.14 K at the optimal doping level of x=0.09.Our report provides a convenient method to synthesize Mo_(3-)xRe_xAl_(2)C within minutes,and also marks the first Re doping study with enhanced superconductivity on the non-centrosymmetric superconductor Mo_(3)Al_(2)C.展开更多
基金Project supported by the National Key Research and Development of China (Grant Nos.2018YFA0704200 and 2021YFA1401800)the National Natural Science Foundation of China (Grant Nos.12074414 and 11774402)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No.XDB25000000)。
文摘We report systematic studies on superconducting properties of the Laves phase superconductor ZrIr_(2).It crystallizes in a C15-type(cubic MgCu_(2)-type,space group Fd3m)structure in which the Ir atoms form a kagome lattice,with cell parameters a=b=c=7.3596(1)?.Resistivity and magnetic susceptibility measurements indicate that ZrIr_(2) is a type-Ⅱsuperconductor with a transition temperature of 4.0 K.The estimated lower and upper critical fields are 12.8 mT and 4.78 T,respectively.Heat capacity measurements confirm the bulk superconductivity in ZrIr_(2).ZrIr_(2) is found to possibly host strong-coupled s-wave superconductivity with the normalized specific heat change△C_(e)/γT_(c)~1.86 and the coupling strength△_(0)/k_BT_(c)~1.92.First-principles calculations suggest that ZrIr_(2) has three-dimensional Fermi surfaces with simple topologies,and the states at Fermi level mainly originate from the Ir-5d and Zr-4d orbitals.Similar to SrIr_(2) and ThIr_(2),spin–orbit coupling has dramatic influences on the band structure in ZrIr_(2).
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11874417 and 12274440)the Strategic Priority Research Program (B) of Chinese Academy of Sciences (Grant No. XDB33010100)the Fund from the Ministry of Science and Technology of China (Grant No. 2022YFA1403903)。
文摘We report a comprehensive study on a layered-structure compound of NaZn_(4)As_(3),which has been predicted to be an ideal topological semimetal(TSM) candidate.It is found that NaZn_(4)As_(3) undergoes a structural transformation from high temperature rhombohedral to a low temperature monoclinic phase.The electric resistivity exhibits a metal-to-insulatorlike transition at around 100 K,and then develops a plateau at low temperature,which might be related to the protected topologically conducting surface states.Our first-principles calculation confirms further that NaZn_(4)As_(3) is a topological insulator(TI) for both different phases rather than a previously proposed TSM.The Hall resistivity reveals that the hole carriers dominate the transport properties for the whole temperature range investigated.Furthermore,an obvious kink possibly associated to the structure transition has been detected in thermopower around ~ 170 K.The large thermopower and moderate κ indicate that NaZn_(4)As_(3) and/or its derivatives can provide a good platform for optimizing and studying the thermoelectric performance.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074414 and 11774402)the National Key Research and Development of China(Grant No.2018YFA0704200)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)。
文摘We report the synthesis,crystal structure,and superconductivity of Ti_(4)Ir_(2)O.The title compound crystallizes in an η-carbide type structure of the space group Fd3m(No.227),with lattice parameters a=b=c=11.6194(1)A.The superconducting temperature T_(c) is found to be 5.1-5.7 K.Most surprisingly,Ti_(4)Ir_(2)O hosts an upper critical field of 16.45 T,which is far beyond the Pauli paramagnetic limit.Strong coupled superconductivity with evidences for multigap is revealed by the measurements of heat capacity and upper critical field.First-principles calculations suggest that the density of states near the Fermi level originates from the hybridization of Ti-3d and Ir-5d orbitals,and the effect of spin-orbit coupling on the Fermi surfaces is prominent.Large values of the Wilson ratio(R_(W)∼3.9),the Kadowaki-Woods ratio[A/γ^(2)∼9.0×10^(−6)µΩ·cm/(mJ·mol^(−1)·K^(−1))^(2)],and the Sommerfeld coefficient(γ=33.74 mJ·mol^(−1)·K^(−2))all suggest strong electron correlations(similar to heavy fermion systems)in Ti_(4)Ir_(2)O.The violation of Pauli limit is possibly due to a combination of strong-coupled superconductivity and large spin-orbit scattering.With these intriguing behaviors,Ti_(4)Ir_(2)O serves as a candidate for unconventional superconductor.
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 Nos 11474339 and 11774402the National Basic Research Program of China under Grant No 2016YFA0300301+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB25000000the Youth Innovation Promotion Association of Chinese Academy of Sciences
文摘We report a direct microwave synthesis method for the preparation of 11-type high quality Fe(Te,Se) polycrystalline superconductors. The bulk samples are rapidly synthesized under the microwave irradiation during several minutes, with a subsequent annealing process at 400℃. The samples exhibit a nearly single phase of the tetragonal PbO-type crystal structure with minor impurities. Morphology characterization shows high density, tight grain connectivity and large grain sizes around 100 μm with small cavities inside the sample. Resistivity and magnetization measurements both show similar superconducting transitions above 14 K. The magnetic hysteresis measurements display broad and symmetric loops without magnetic background, and a high critical current density J_c about 1.2 × 10~4 A/cm^2 at 2 K and 7 T is estimated by the Bean model. Compared with the solidstate reaction synthesized samples, these superconducting bulks from microwave-assisted synthesis are possibly free of the interstitial Fe due to smaller c-axis, higher T_c in magnetic transitions, better M–H loops without magnetic background and greatly enhanced J_c, and are promising as raw materials for the non-toxic Fe-based superconducting wires for large currents and high field applications.
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 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.
基金the National Key Research and Development of China(Grant Nos.2018YFA0704200 and 2016YFA0300301)the National Natural Science Foundation of China(Grant Nos.12074414 and 11774402)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)。
文摘We report the microwave synthesis and the doping effect of Mo_(3-)xRe_xAl_(2)C(0≤x≤0.3)superconductor.Re doping into Mo_(3)Al_(2)C results in a regular shrinkage of the lattice,marked by the linear decrease of lattice parameter a from6.868(1)A(for Mo_(3)Al_(2)C)to 6.846(2)A(for Mo_(2.7)Re_(0.3)Al_(2)C).Upon Re doping,T_(c)of Mo_(3-x)Re_xAl_(2)C first increases and then decreases,with the maximum T_(c)=9.14 K at the optimal doping level of x=0.09.Our report provides a convenient method to synthesize Mo_(3-)xRe_xAl_(2)C within minutes,and also marks the first Re doping study with enhanced superconductivity on the non-centrosymmetric superconductor Mo_(3)Al_(2)C.
基金supported by the National Key Research and Development Program of China(2018YFA0704200,2021YFA1401800,2018YFA0305602,and 2017YFA0302904)the National Natural Science Foundation of China(12074414,12074002,and 11774402)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB25000000)。
