Seeking new order parameters and the related broken symmetry and studying their relationship with phase transition have been important topics in condensed matter physics.Here,by using spin-and angle-resolved photoemis...Seeking new order parameters and the related broken symmetry and studying their relationship with phase transition have been important topics in condensed matter physics.Here,by using spin-and angle-resolved photoemission spectroscopy,we confirm the helical spin texture caused by spin-layer locking in the nodal region in the cuprate superconductor Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)and discover the anisotropy of spin polarizations at nodes alongΓ–X andΓ–Y directions.The breaking of C_(4)rotational symmetry in electronic spin texture may give deeper insights into understanding the ground state of cuprate superconductors.展开更多
High resolution laser-based angle-resolved photoemission measurements are carried out on an overdoped superconductor Bi_2Sr_2CaCu_2O_(8+)with a_(c )of 75 K.Two Fermi surface sheets caused by bilayer splitting are clea...High resolution laser-based angle-resolved photoemission measurements are carried out on an overdoped superconductor Bi_2Sr_2CaCu_2O_(8+)with a_(c )of 75 K.Two Fermi surface sheets caused by bilayer splitting are clearly identified with rather different doping levels:the bonding sheet corresponds to a doping level of 0.14,which is slightly underdoped while the antibonding sheet has a doping of 0.27 that is heavily overdoped,giving an overall doping level of 0.20 for the sample.Different superconducting gap sizes on the two Fermi surface sheets are revealed.The superconducting gap on the antibonding Fermi surface sheet follows a standard d-wave form while it deviates from the standard d-wave form for the bonding Fermi surface sheet.The maximum gap difference between the two Fermi surface sheets near the antinodal region is~2 meV.These observations provide important information for studying the relationship between the Fermi surface topology and superconductivity,and the layer-dependent superconductivity in high temperature cuprate superconductors.展开更多
As a typical hole-doped cuprate superconductor,Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi2212)carrier doping is mostly determined by its oxygen content.Traditional doping methods can regulate its doping level within the range of...As a typical hole-doped cuprate superconductor,Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi2212)carrier doping is mostly determined by its oxygen content.Traditional doping methods can regulate its doping level within the range of hole doping.Here we report the first application of CaH_(2)annealing method in regulating the doping level of Bi2212.By continuously controlling the anneal time,a series of differently doped samples can be obtained.The combined experimental results of x-ray diffraction,scanning transmission electron microscopy,resistance and Hall measurements demonstrate that the CaH_(2)induced topochemical reaction can effectively change the oxygen content of Bi2212 within a very wide range,even switching from hole doping to electron doping.We also found evidence of a low-T_c superconducting phase in the electron doping side.展开更多
We carry out detailed momentum-dependent and temperature-dependent measurements on Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi2212)superconductor in the superconducting and pseudogap states by super-high resolution laser-based an...We carry out detailed momentum-dependent and temperature-dependent measurements on Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi2212)superconductor in the superconducting and pseudogap states by super-high resolution laser-based angleresolved photoemission spectroscopy.The precise determination of the superconducting gap for the nearly optimally doped Bi2212(T_(c)=91 K)at low temperature indicates that the momentum-dependence of the superconducting gap deviates from the standard d-wave form(cos(2Φ)).It can be alternatively fitted by including a high-order term(cos(6Φ))in which the next nearest-neighbor interaction is considered.We find that the band structure near the antinodal region smoothly evolves across the pseudogap temperature without a signature of band reorganization which is distinct from that found in Bi_(2)Sr_(2)CuO_(6+δ)superconductors.This indicates that the band reorganization across the pseudogap temperature is not a universal behavior in cuprate superconductors.These results provide new insights in understanding the nature of the superconducting gap and pseudogap in high-temperature cuprate superconductors.展开更多
The pairing mechanism of high-temperature superconductivity in cuprates remains the biggest unresolved mystery in condensed matter physics. To solve the problem, one of the most effective approaches is to investigate ...The pairing mechanism of high-temperature superconductivity in cuprates remains the biggest unresolved mystery in condensed matter physics. To solve the problem, one of the most effective approaches is to investigate directly the superconducting CuO2 layers. Here, by growing CuO2 monolayer films on Bi2Sr2CaCu2O8+δ substrates, we identify two distinct and spatially separated energy gaps centered at the Fermi energy, a smaller U-like gap and a larger V-like gap on the films, and study their interactions with alien atoms by low-temperature scanning tunneling microscopy. The newly discovered U-like gap exhibits strong phase coherence and is immune to scattering by K, Cs and Ag atoms, suggesting its nature as a nodeless superconducting gap in the CuO2 layers, whereas the V-like gap agrees with the well-known pseudogap state in the underdoped regime. Our results support an s-wave superconductivity in Bi2Sr2CaCu2O8+δ, which, we pro- pose, originates from the modulation-doping resultant twodimensional hole liquid confined in the CuO2 layers.展开更多
基金the National Natural Science Foundation of China(Grant Nos.U1632266,11927807,and U2032207)the National Key R&D Program of China(Grant No.2017YFA 0305400)supported by the US Department of Energy,Office of Basic Energy Sciences(Grant Nos.DOE-sc0012704)。
文摘Seeking new order parameters and the related broken symmetry and studying their relationship with phase transition have been important topics in condensed matter physics.Here,by using spin-and angle-resolved photoemission spectroscopy,we confirm the helical spin texture caused by spin-layer locking in the nodal region in the cuprate superconductor Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)and discover the anisotropy of spin polarizations at nodes alongΓ–X andΓ–Y directions.The breaking of C_(4)rotational symmetry in electronic spin texture may give deeper insights into understanding the ground state of cuprate superconductors.
基金Supported by the National Natural Science Foundation of China under Grant No 11888101the National Key Research and Development Program of China under Grant Nos 2016YFA0300300 and 2017YFA0302900+3 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB25000000)the Youth Innovation Promotion Association of CAS under Grant No2017013the Research Program of Beijing Academy of Quantum Information Sciences under Grant No Y18G06supported by the Office of Basic Energy Sciences,U.S.Department of Energy(DOE)under Contract No de-sc0012704
文摘High resolution laser-based angle-resolved photoemission measurements are carried out on an overdoped superconductor Bi_2Sr_2CaCu_2O_(8+)with a_(c )of 75 K.Two Fermi surface sheets caused by bilayer splitting are clearly identified with rather different doping levels:the bonding sheet corresponds to a doping level of 0.14,which is slightly underdoped while the antibonding sheet has a doping of 0.27 that is heavily overdoped,giving an overall doping level of 0.20 for the sample.Different superconducting gap sizes on the two Fermi surface sheets are revealed.The superconducting gap on the antibonding Fermi surface sheet follows a standard d-wave form while it deviates from the standard d-wave form for the bonding Fermi surface sheet.The maximum gap difference between the two Fermi surface sheets near the antinodal region is~2 meV.These observations provide important information for studying the relationship between the Fermi surface topology and superconductivity,and the layer-dependent superconductivity in high temperature cuprate superconductors.
基金supported by the National Natural Science Foundation of China(Grant Nos.11888101 and U1832202)the Chinese Academy of Sciences(Grant Nos.QYZDB-SSWSLH043 and XDB33000000)+4 种基金the K.C.Wong Education Foundation(Grant No.GJTD-2018-01)the Informatization Plan of Chinese Academy of Sciences(Grant No.CAS-WX2021SF-0102)supported by the Synergetic Extreme Condition User Facility(SECUF)supported by China Postdoctoral Science Foundation(Grant Nos.2020M680726 and YJ20200325)supported by US DOE(Grant Nos.DE-SC0010526 and DE-SC0012704)。
文摘As a typical hole-doped cuprate superconductor,Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi2212)carrier doping is mostly determined by its oxygen content.Traditional doping methods can regulate its doping level within the range of hole doping.Here we report the first application of CaH_(2)annealing method in regulating the doping level of Bi2212.By continuously controlling the anneal time,a series of differently doped samples can be obtained.The combined experimental results of x-ray diffraction,scanning transmission electron microscopy,resistance and Hall measurements demonstrate that the CaH_(2)induced topochemical reaction can effectively change the oxygen content of Bi2212 within a very wide range,even switching from hole doping to electron doping.We also found evidence of a low-T_c superconducting phase in the electron doping side.
基金Supported by the National Key Research and Development Program of China under Grant No 2016YFA0300300the National Natural Science Foundation of China under Grant No 11334010+1 种基金the National Basic Research Program of China under Grant No2015CB921300the Strategic Priority Research Program(B)of the Chinese Academy of Sciences under Grant No XDB07020300
文摘We carry out detailed momentum-dependent and temperature-dependent measurements on Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi2212)superconductor in the superconducting and pseudogap states by super-high resolution laser-based angleresolved photoemission spectroscopy.The precise determination of the superconducting gap for the nearly optimally doped Bi2212(T_(c)=91 K)at low temperature indicates that the momentum-dependence of the superconducting gap deviates from the standard d-wave form(cos(2Φ)).It can be alternatively fitted by including a high-order term(cos(6Φ))in which the next nearest-neighbor interaction is considered.We find that the band structure near the antinodal region smoothly evolves across the pseudogap temperature without a signature of band reorganization which is distinct from that found in Bi_(2)Sr_(2)CuO_(6+δ)superconductors.This indicates that the band reorganization across the pseudogap temperature is not a universal behavior in cuprate superconductors.These results provide new insights in understanding the nature of the superconducting gap and pseudogap in high-temperature cuprate superconductors.
基金Acknowledgments The work was financially supported by the National Natural Science Foundation, Ministry of Science and Technology and Ministry of Education of China. The work at Brookhaven National Laboratory was supported by the Office of Basic Energy Sciences, US Department of Energy, under Contract No. DE- SC00112704.
文摘The pairing mechanism of high-temperature superconductivity in cuprates remains the biggest unresolved mystery in condensed matter physics. To solve the problem, one of the most effective approaches is to investigate directly the superconducting CuO2 layers. Here, by growing CuO2 monolayer films on Bi2Sr2CaCu2O8+δ substrates, we identify two distinct and spatially separated energy gaps centered at the Fermi energy, a smaller U-like gap and a larger V-like gap on the films, and study their interactions with alien atoms by low-temperature scanning tunneling microscopy. The newly discovered U-like gap exhibits strong phase coherence and is immune to scattering by K, Cs and Ag atoms, suggesting its nature as a nodeless superconducting gap in the CuO2 layers, whereas the V-like gap agrees with the well-known pseudogap state in the underdoped regime. Our results support an s-wave superconductivity in Bi2Sr2CaCu2O8+δ, which, we pro- pose, originates from the modulation-doping resultant twodimensional hole liquid confined in the CuO2 layers.