Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/spectroscopy, we clearly ...Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/spectroscopy, we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi2Sr2CaCu2O8＋δ （Bi2212） and YBa2Cu3O7-x （YBCO） along their c-axes on a scale shorter than the interlayer spacing. By tunneling into the （100） plane of a Bi2212 single crystal and a YBCO film, we observe both U-shaped tunneling spectra with extended fiat zero-conductance bottoms, and V-shaped gap structures, in different regions of each sample. On the YBCO film, tunneling into a （110） surface only reveals a U-shaped gap without any zero-bias peak. Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap. The V-shaped gap has a very small amplitude, and is likely proximity-induced by regions having the larger U-shaped gap.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
We report a reproducible approach in preparing high-quality overdoped Bi2 Sr2 CaCu2 08＋δ （Bi2212） single crystals by annealing Bi2212 crystals in high oxygen pressure followed by a fast quenching. In this way, hig...We report a reproducible approach in preparing high-quality overdoped Bi2 Sr2 CaCu2 08＋δ （Bi2212） single crystals by annealing Bi2212 crystals in high oxygen pressure followed by a fast quenching. In this way, high-quality overdoped and heavily overdoped Bi2212 single crystals are obtained by controlling the annealing oxygen pressure. We find that, beyond a limit of oxygen pressure that can achieve most heavily overdoped Bi2212 with a Tc N63 K, the annealed Bi2212 begins to decompose. This accounts for the existence of the hole-doping limit and thus the Tc limit in the heavily overdoped region of Bi2212 by the oxygen annealing process. These results provide a reliable way in preparing high-quality overdoped and heavily overdoped Bi2212 crystals that are important for studies of the physical properties, electronic structure and superconductivity mechanism of the cuprate superconductors.展开更多
A modified spark plasma sintering（SPS） technique was developed for the fabrication of Bi2Sr2CaCu2Ox（Bi-2212）superconducting bulks with better intergrain connections. The influences of the modified SPS process on t...A modified spark plasma sintering（SPS） technique was developed for the fabrication of Bi2Sr2CaCu2Ox（Bi-2212）superconducting bulks with better intergrain connections. The influences of the modified SPS process on the microstructures, intergrain connections, and related superconducting properties were systematically analyzed. The modified SPS process can not only increase the final density of the bulk samples but also enhance the texture structures. Clean grain boundaries were obtained instead of the intergrain amorphous layers. Therefore the intergranular properties were obviously improved. Due to the better intergrain connections and the stronger flux pinning properties, the critical current densities of the Bi-2212 bulks obtained via the modified SPS process were greatly increased. The obtained improvements imply the possibility for the modified SPS technique to be used for enhancing the superconducting properties of the Bi-2212 tapes.展开更多
We adopted a new method, acid etching process, to fabricate the intrinsic Josephson junctions based on the Bi2Sr2CaCu2O8+x single crystals. By soaking the crystals into the dilute hydrochloric acid, we fabricated a ju...We adopted a new method, acid etching process, to fabricate the intrinsic Josephson junctions based on the Bi2Sr2CaCu2O8+x single crystals. By soaking the crystals into the dilute hydrochloric acid, we fabricated a junction stack successfully, and meantime made the surrounding area insulated. A certain concentration of hydrochloric acid was used to maintain the roughness of the modified layer. The cur-rent-voltage characteristic was achieved through the four terminal measurement. We could control the junctions' number by changing the concentration and the soaking time. We also found that the thick-ness of the stack was equal to the average height of the insulation layer. Such a simple, convenient and controllable fabrication method with a high yield might widen the applications of the intrinsic Joseph-son junctions.展开更多
Using intrinsic Josephson junctions in Ba<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+x</sub> single crystal, harmonic frequency mixing at 8 and 3 mm wavebands was ...Using intrinsic Josephson junctions in Ba<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+x</sub> single crystal, harmonic frequency mixing at 8 and 3 mm wavebands was successfully demonstrated at liquid nitrogen temperatures with harmonic numbers up to 68 and 50 respectively. The dependences of intermediate frequency output on the local oscillator power and dc bias were carefully studied.展开更多
基金Supported by the National Natural Science Foundation of Chinathe National Key Research and Development Program of China under Grant No 2016YFA0300203
文摘Pairing in the cuprate high-temperature superconductors and its origin remain among the most enduring mysteries in condensed matter physics. With cross-sectional scanning tunneling microscopy/spectroscopy, we clearly reveal the spatial-dependence or inhomogeneity of the superconducting gap structure of Bi2Sr2CaCu2O8＋δ （Bi2212） and YBa2Cu3O7-x （YBCO） along their c-axes on a scale shorter than the interlayer spacing. By tunneling into the （100） plane of a Bi2212 single crystal and a YBCO film, we observe both U-shaped tunneling spectra with extended fiat zero-conductance bottoms, and V-shaped gap structures, in different regions of each sample. On the YBCO film, tunneling into a （110） surface only reveals a U-shaped gap without any zero-bias peak. Our analysis suggests that the U-shaped gap is likely a nodeless superconducting gap. The V-shaped gap has a very small amplitude, and is likely proximity-induced by regions having the larger U-shaped gap.
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 under Grant Nos 11190022,11334010 and 11534007the National Basic Research Program of China under Grant No 2015CB921000the Strategic Priority Research Program(B)of Chinese Academy of Sciences under Grant No XDB07020300
文摘We report a reproducible approach in preparing high-quality overdoped Bi2 Sr2 CaCu2 08＋δ （Bi2212） single crystals by annealing Bi2212 crystals in high oxygen pressure followed by a fast quenching. In this way, high-quality overdoped and heavily overdoped Bi2212 single crystals are obtained by controlling the annealing oxygen pressure. We find that, beyond a limit of oxygen pressure that can achieve most heavily overdoped Bi2212 with a Tc N63 K, the annealed Bi2212 begins to decompose. This accounts for the existence of the hole-doping limit and thus the Tc limit in the heavily overdoped region of Bi2212 by the oxygen annealing process. These results provide a reliable way in preparing high-quality overdoped and heavily overdoped Bi2212 crystals that are important for studies of the physical properties, electronic structure and superconductivity mechanism of the cuprate superconductors.
基金Project supported by the National Basic Research Program of China(Grant No.2011CBA00104)the National Natural Science Foundation of China(Grant No.51472206)+1 种基金the ITER Project of China(Grant No.2013GB110001)the Program for Innovative Research Team in Shaanxi Province,China(Grant No.2013KCT-07)
文摘A modified spark plasma sintering（SPS） technique was developed for the fabrication of Bi2Sr2CaCu2Ox（Bi-2212）superconducting bulks with better intergrain connections. The influences of the modified SPS process on the microstructures, intergrain connections, and related superconducting properties were systematically analyzed. The modified SPS process can not only increase the final density of the bulk samples but also enhance the texture structures. Clean grain boundaries were obtained instead of the intergrain amorphous layers. Therefore the intergranular properties were obviously improved. Due to the better intergrain connections and the stronger flux pinning properties, the critical current densities of the Bi-2212 bulks obtained via the modified SPS process were greatly increased. The obtained improvements imply the possibility for the modified SPS technique to be used for enhancing the superconducting properties of the Bi-2212 tapes.
基金the National Natural Science Foundation of China (Grants Nos.10474036, 60571007 and 10390163)the National Basic Research Program of China (Grant No. 2006CB601006)the Specialized Research Fund for the Doc-toral Program of Higher Education of China (Grant No. 2004028033)
文摘We adopted a new method, acid etching process, to fabricate the intrinsic Josephson junctions based on the Bi2Sr2CaCu2O8+x single crystals. By soaking the crystals into the dilute hydrochloric acid, we fabricated a junction stack successfully, and meantime made the surrounding area insulated. A certain concentration of hydrochloric acid was used to maintain the roughness of the modified layer. The cur-rent-voltage characteristic was achieved through the four terminal measurement. We could control the junctions' number by changing the concentration and the soaking time. We also found that the thick-ness of the stack was equal to the average height of the insulation layer. Such a simple, convenient and controllable fabrication method with a high yield might widen the applications of the intrinsic Joseph-son junctions.
文摘Using intrinsic Josephson junctions in Ba<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+x</sub> single crystal, harmonic frequency mixing at 8 and 3 mm wavebands was successfully demonstrated at liquid nitrogen temperatures with harmonic numbers up to 68 and 50 respectively. The dependences of intermediate frequency output on the local oscillator power and dc bias were carefully studied.
