We perform systematic thermal conductivity measurements on heavily hole-doped Ba1-xKxFe2As2 single crystals with 0.747 ≤ x ≤ 0.974. At x=0.747, the K0/T is negligible, indicating a nodeless superconducting gap. A sm...We perform systematic thermal conductivity measurements on heavily hole-doped Ba1-xKxFe2As2 single crystals with 0.747 ≤ x ≤ 0.974. At x=0.747, the K0/T is negligible, indicating a nodeless superconducting gap. A small residual linear term K0/T （=0.035 m W.K-2 cm-1） appears at xz0.826, and it increases slowly up to x=0.974, followed by a substantial increase of more than 20 times to of K0/T clearly shows that the nodal gap appears near x surface topology. The small values of K0/T from x=0.826 the pure KFe2As2 （x=1.0）. This doping dependence = 0.8, possibly associated with the change of Fermi to 0.974 are consistent with the Y-shaped nodal s- wave gap recently revealed by angle-resolved photoemission spectroscopy experiments at x=0.9. Furthermore, the substantial increase of K0/T from x=0.974 to 1.0 is inconsistent with a symmetry-imposed d-wave gap in KFe2 As2, and a possible nodal gap structure in KFe2As2 is discussed.展开更多
Metal-insulator transition(MIT)in perovskite iridium oxides Sr_(n+1)IrnO_(3n+1)represents one of the most attractive phenomena exemplifying the cooperation of Coulomb interaction and spin-orbit coupling(SOC).MIT takes...Metal-insulator transition(MIT)in perovskite iridium oxides Sr_(n+1)IrnO_(3n+1)represents one of the most attractive phenomena exemplifying the cooperation of Coulomb interaction and spin-orbit coupling(SOC).MIT takes place when Sr_(n+1)IrnO_(3n+1)(n=1,2)is doped with carriers.While electron-doped Sr_(n+1)IrnO_(3n+1)(n=1,2)systems have been extensively investigated,hole-doped samples are still limited.Here,we report the first growth of Fe-doped(hole-doped)Sr_(3)Ir_(2)O_(7)single crystals[Sr_3(Ir_(1-x)Fe_x)_(2)O_(7)]with the doping level 0.1≤x≤0.28.An MIT behavior is observed at the doping level of x~0.16 from resistivity measurements.Electronic structures of Fe-doped Sr_(3)Ir_(2)O_(7)have been revealed by angle-resolved photoemission spectroscopy(ARPES)measurements.The evident energy shift of the band structure indicates higher hole-doping level as compared with Rh-doped Sr_(3)Ir_(2)O_(7).Our results demonstrate that Fe doping serves as an effective approach for heavily hole doping in Sr_(3)Ir_(2)O_(7),thereby offering a powerful strategy to modulate MIT in this material system.展开更多
Nickel-based superconductors have attracted great attention due to the finding of the Ruddlesden-Popper(R-P)bilayer nickelate La_(3)Ni_(2)O_(7)with superconducting critical temperature(T_(c))of 80 K at pressure above ...Nickel-based superconductors have attracted great attention due to the finding of the Ruddlesden-Popper(R-P)bilayer nickelate La_(3)Ni_(2)O_(7)with superconducting critical temperature(T_(c))of 80 K at pressure above 14 GPa.Recent efforts have been devoted to the study of La_(2)PrNi_(2)O_(7),while the detailed structure remains unclear.In this work,we explore the stability and physical properties of such an interesting system by using density functional theory and the U parameter simulation method implemented in VASP.The results show that the enthalpy of La_(2)PrNi_(2)O_(7)is slightly larger than its parent material bilayer R-P nickelate La_(3)Ni_(2)O_(7).The electronic structure analysis indicates that near the Fermi level,the eg orbit of Ni dominates and strongly hybridizes with the 2p orbit of O,thereby forming a significant van Hove singularity that is conducive to superconductivity.The Amam phase to the I4/mmm phase occurs,accompanied by an increase in the bandwidth of Ni 3d_(z)_(2) and an enhancement of the bonding-antibonding splitting(from about 0.5 eV to 1.5 eV),which leads to an increase in the density of states at the Fermi level.Our findings provide insights into the preparation and superconductivity of R-P bilayer nickelate.展开更多
The recent discovery of pressure-induced superconductivity in La_(3)Ni_(2)O_(7)has established a novel platform for studying unconventional superconductors.However,achieving superconductivity in this system currently ...The recent discovery of pressure-induced superconductivity in La_(3)Ni_(2)O_(7)has established a novel platform for studying unconventional superconductors.However,achieving superconductivity in this system currently requires relatively high pressures.In this study,we propose a chemical pressure strategy via Sr substitution to stabilize high-Tcsuperconductivity in La_(3)Ni_(2)O_(7)under ambient conditions.Using density functional theory(DFT)calculations,we systematically investigate the structural and electronic properties of Sr-doped La_(3-x)Sr_(x)Ni_(2)O_(7)(x=0.25,0.5,1)at ambient pressure and identify two dynamically stable phases:La_(2.5)Sr_(0.5)Ni_(2)O_(7)and La2SrNi2O7.Our calculations reveal that both phases exhibit metallization of theσ-bonding bands dominated by Ni-d_(z)2orbitals—a key feature associated with high-Tcsuperconductivity,as reported in the high-pressure phase of La_(3)Ni_(2)O_(7).Further analysis using tight-binding models shows that the key hopping parameters in La_(2.5)Sr_(0.5)Ni_(2)O_(7)and La2SrNi2O7closely resemble those of La_(3)Ni_(2)O_(7)under high pressure,indicating that strong superexchange interactions between interlayer Ni-dz2orbitals are preserved.These findings suggest that the doped phases may provide a promising platform for exploring superconductivity,which requires further experimental validation.展开更多
We report the crystal growth of a new hole-doped iron-based superconductor Ba(Fe_(0.875)Ti_(0.125))_(2)As_(2)by substituting Ti on the Fe site.The crystals are accidentally obtained in trying to grow Ni doped Ba_(2)Ti...We report the crystal growth of a new hole-doped iron-based superconductor Ba(Fe_(0.875)Ti_(0.125))_(2)As_(2)by substituting Ti on the Fe site.The crystals are accidentally obtained in trying to grow Ni doped Ba_(2)Ti_(2)Fe_(2)As_(4)O.After annealing at 500℃ in vacuum for one week,superconductivity is observed with zero resistance at T_(c0)≈17.5 K,and about 20%diamagnetic volume down to 2 K.While both the small anisotropy of superconductivity and the temperature dependence of normal state resistivity are akin to the electron doped 122-type compounds,the Hall coefficient is positive and similar to the case in hole-doped Ba_(0.9)K_(0.1)Fe_(2)As2.The density functional theory calculations suggest dominated hole pockets contributed by Fe/Ti 3d orbitals.Therefore,the Ba(Fe_(1-x)Ti_(x))_(2)As_(2)system provides a new platform to study the superconductivity with hole doping on the Fe site of iron-based superconductors.展开更多
We synthesized a series of Nb2Pd1-xRuxS5 polycrystalline samples by a solid-state reaction method and systematically investigated the Ru-doping effect on superconductivity by transport and magnetic measurements. It is...We synthesized a series of Nb2Pd1-xRuxS5 polycrystalline samples by a solid-state reaction method and systematically investigated the Ru-doping effect on superconductivity by transport and magnetic measurements. It is found that superconductivity is enhanced with Ru doping and is quite robust upon disorder. Hall coefficient measurements indicate that the charge transport is dominated by hole-type charge carriers similar to the case of Ir doping, suggesting multi-band superconductivity. Upon Ru or Ir doping, Hc2/Tc exhibits a significant enhancement, exceeding the Pauli paramagnetic limit value by a factor of approximately 4. A comparison of Tc and the upper critical field （Hc2） amongst the different doping elements on Pd site, reveals a significant role of spin-orbit coupling.展开更多
基金Supported by the National Basic Research Program under Grant Nos 2012CB821402 and 2015CB921401the National Natural Science Foundation of China+1 种基金the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher LearningSTCSM of China(No 15XD1500200)
文摘We perform systematic thermal conductivity measurements on heavily hole-doped Ba1-xKxFe2As2 single crystals with 0.747 ≤ x ≤ 0.974. At x=0.747, the K0/T is negligible, indicating a nodeless superconducting gap. A small residual linear term K0/T （=0.035 m W.K-2 cm-1） appears at xz0.826, and it increases slowly up to x=0.974, followed by a substantial increase of more than 20 times to of K0/T clearly shows that the nodal gap appears near x surface topology. The small values of K0/T from x=0.826 the pure KFe2As2 （x=1.0）. This doping dependence = 0.8, possibly associated with the change of Fermi to 0.974 are consistent with the Y-shaped nodal s- wave gap recently revealed by angle-resolved photoemission spectroscopy experiments at x=0.9. Furthermore, the substantial increase of K0/T from x=0.974 to 1.0 is inconsistent with a symmetry-imposed d-wave gap in KFe2 As2, and a possible nodal gap structure in KFe2As2 is discussed.
基金supported by the National Natural Science Foundation of China(Grant No.12074358)the National Key Research and Development Program of China(Grant No.2024YFA1408103)+2 种基金the International Partnership Program of the Chinese Academy of Sciences(Grant No.123GJHZ2022035MI)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302802)the Fundamental Research Funds for the Central Universities(Grant No.WK3510000015)。
文摘Metal-insulator transition(MIT)in perovskite iridium oxides Sr_(n+1)IrnO_(3n+1)represents one of the most attractive phenomena exemplifying the cooperation of Coulomb interaction and spin-orbit coupling(SOC).MIT takes place when Sr_(n+1)IrnO_(3n+1)(n=1,2)is doped with carriers.While electron-doped Sr_(n+1)IrnO_(3n+1)(n=1,2)systems have been extensively investigated,hole-doped samples are still limited.Here,we report the first growth of Fe-doped(hole-doped)Sr_(3)Ir_(2)O_(7)single crystals[Sr_3(Ir_(1-x)Fe_x)_(2)O_(7)]with the doping level 0.1≤x≤0.28.An MIT behavior is observed at the doping level of x~0.16 from resistivity measurements.Electronic structures of Fe-doped Sr_(3)Ir_(2)O_(7)have been revealed by angle-resolved photoemission spectroscopy(ARPES)measurements.The evident energy shift of the band structure indicates higher hole-doping level as compared with Rh-doped Sr_(3)Ir_(2)O_(7).Our results demonstrate that Fe doping serves as an effective approach for heavily hole doping in Sr_(3)Ir_(2)O_(7),thereby offering a powerful strategy to modulate MIT in this material system.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFA1406103)the Education Department of Jilin Province,and Science and Technology Plan(Grant No.JJKH20211042KJ).
文摘Nickel-based superconductors have attracted great attention due to the finding of the Ruddlesden-Popper(R-P)bilayer nickelate La_(3)Ni_(2)O_(7)with superconducting critical temperature(T_(c))of 80 K at pressure above 14 GPa.Recent efforts have been devoted to the study of La_(2)PrNi_(2)O_(7),while the detailed structure remains unclear.In this work,we explore the stability and physical properties of such an interesting system by using density functional theory and the U parameter simulation method implemented in VASP.The results show that the enthalpy of La_(2)PrNi_(2)O_(7)is slightly larger than its parent material bilayer R-P nickelate La_(3)Ni_(2)O_(7).The electronic structure analysis indicates that near the Fermi level,the eg orbit of Ni dominates and strongly hybridizes with the 2p orbit of O,thereby forming a significant van Hove singularity that is conducive to superconductivity.The Amam phase to the I4/mmm phase occurs,accompanied by an increase in the bandwidth of Ni 3d_(z)_(2) and an enhancement of the bonding-antibonding splitting(from about 0.5 eV to 1.5 eV),which leads to an increase in the density of states at the Fermi level.Our findings provide insights into the preparation and superconductivity of R-P bilayer nickelate.
基金funding from the National Key R&D Program of China(Grant No.2023YFA1610000)the National Natural Science Foundation of China(Grant No.12304036)+3 种基金the Open Project of Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices(Grant No.2022B1212010008)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2023A1515010071)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.23xkjc016)funding from the National Natural Science Foundation of China(Grant Nos.12494594 and 12274472)。
文摘The recent discovery of pressure-induced superconductivity in La_(3)Ni_(2)O_(7)has established a novel platform for studying unconventional superconductors.However,achieving superconductivity in this system currently requires relatively high pressures.In this study,we propose a chemical pressure strategy via Sr substitution to stabilize high-Tcsuperconductivity in La_(3)Ni_(2)O_(7)under ambient conditions.Using density functional theory(DFT)calculations,we systematically investigate the structural and electronic properties of Sr-doped La_(3-x)Sr_(x)Ni_(2)O_(7)(x=0.25,0.5,1)at ambient pressure and identify two dynamically stable phases:La_(2.5)Sr_(0.5)Ni_(2)O_(7)and La2SrNi2O7.Our calculations reveal that both phases exhibit metallization of theσ-bonding bands dominated by Ni-d_(z)2orbitals—a key feature associated with high-Tcsuperconductivity,as reported in the high-pressure phase of La_(3)Ni_(2)O_(7).Further analysis using tight-binding models shows that the key hopping parameters in La_(2.5)Sr_(0.5)Ni_(2)O_(7)and La2SrNi2O7closely resemble those of La_(3)Ni_(2)O_(7)under high pressure,indicating that strong superexchange interactions between interlayer Ni-dz2orbitals are preserved.These findings suggest that the doped phases may provide a promising platform for exploring superconductivity,which requires further experimental validation.
基金supported by the National Key R&D Program of China(Grant Nos.2023YFA1406100,2022YFA1403800,2022YFA1403400,and 2021YFA1400400)the National Natural Science Foundation of China(Grant Nos.12274444 and 12574165)+1 种基金the Chinese Academy of Sciences(Grant No.XDB25000000)financial support from HBNI-RRCAT。
文摘We report the crystal growth of a new hole-doped iron-based superconductor Ba(Fe_(0.875)Ti_(0.125))_(2)As_(2)by substituting Ti on the Fe site.The crystals are accidentally obtained in trying to grow Ni doped Ba_(2)Ti_(2)Fe_(2)As_(4)O.After annealing at 500℃ in vacuum for one week,superconductivity is observed with zero resistance at T_(c0)≈17.5 K,and about 20%diamagnetic volume down to 2 K.While both the small anisotropy of superconductivity and the temperature dependence of normal state resistivity are akin to the electron doped 122-type compounds,the Hall coefficient is positive and similar to the case in hole-doped Ba_(0.9)K_(0.1)Fe_(2)As2.The density functional theory calculations suggest dominated hole pockets contributed by Fe/Ti 3d orbitals.Therefore,the Ba(Fe_(1-x)Ti_(x))_(2)As_(2)system provides a new platform to study the superconductivity with hole doping on the Fe site of iron-based superconductors.
基金Acknowledgements The authors would like to thank Guanghan Cao for helpful discussions. This work was supported by the Ministry of Science and Technology of China （Grant Nos. 2014CB921203 and 2016YFA0300402）, the National Natural Science Foundation of China （Contract Nos. U1332209 and 11190023）, the Ministry of Education of China （Contract No. 2015KF07）, and the Fundamental Research Funds for the Central Universities of China.
文摘We synthesized a series of Nb2Pd1-xRuxS5 polycrystalline samples by a solid-state reaction method and systematically investigated the Ru-doping effect on superconductivity by transport and magnetic measurements. It is found that superconductivity is enhanced with Ru doping and is quite robust upon disorder. Hall coefficient measurements indicate that the charge transport is dominated by hole-type charge carriers similar to the case of Ir doping, suggesting multi-band superconductivity. Upon Ru or Ir doping, Hc2/Tc exhibits a significant enhancement, exceeding the Pauli paramagnetic limit value by a factor of approximately 4. A comparison of Tc and the upper critical field （Hc2） amongst the different doping elements on Pd site, reveals a significant role of spin-orbit coupling.
