High-T_(c)superconductivity with possible T_(c)≈80 K has been reported in the single crystal of La_(3)Ni_(2)O_(7)under high pressure.Based on the electronic structure given by the density functional theory calculatio...High-T_(c)superconductivity with possible T_(c)≈80 K has been reported in the single crystal of La_(3)Ni_(2)O_(7)under high pressure.Based on the electronic structure given by the density functional theory calculations,we propose an effective bi-layer model Hamiltonian including both 3d_(z)^(2)and 3d_((x)^(2)-(y)^(2))orbital electrons of the nickel cations.The main feature of the model is that the 3d_(z)^(2)electrons form inter-layerσ-bonding and anti-bonding bands via the apical oxygen anions between the two layers,while the 3d_((x)^(2)-(y)^(2))electrons hybridize with the 3d_(z)^(2)electrons within each NiO_(2)plane.The chemical potential difference of these two orbital electrons ensures that the 3d_(z)^(2)orbitals are close to half-filling and the 3d_((x)^(2)-(y)^(2))orbitals are near quarter-filling.The strong on-site Hubbard repulsion of the 3d_(z)^(2)orbital electrons gives rise to an effective inter-layer antiferromagnetic spin super-exchange J.Applying pressure can self dope holes on the 3d_(z)^(2)orbitals with the same amount of electrons doped on the 3d_((x)^(2)-(y)^(2))orbitals.By performing numerical density-matrix renormalization group calculations on a minimum setup and focusing on the limit of large J and small doping of 3d_(z)^(2)orbitals,we find the superconducting instability on both the 3d_(z)^(2)and3d_((x)^(2)-(y)^(2))orbitals by calculating the equal-time spin singlet pair–pair correlation function.Our numerical results may provide useful insights in the high-T_(c)superconductivity in single crystal La_(3)Ni_(2)O_(7)under high pressure.展开更多
The recent report of pressure-induced structural transition and signature of superconductivity with T_(c)≈80 K above 14 GPa in La_(3)Ni_(2)O_(7)crystals has garnered considerable attention.To further elaborate this d...The recent report of pressure-induced structural transition and signature of superconductivity with T_(c)≈80 K above 14 GPa in La_(3)Ni_(2)O_(7)crystals has garnered considerable attention.To further elaborate this discovery,we carried out comprehensive resistance measurements on La_(3)Ni_(2)O_(7)crystals grown in an optical-image floating zone furnace under oxygen pressure(15 bar)using a diamond anvil cell(DAC)and cubic anvil cell(CAC),which employ a solid(KBr)and liquid(glycerol)pressure-transmitting medium,respectively.Sample 1 measured in the DAC exhibits a semiconducting-like behavior with large resistance at low pressures and gradually becomes metallic upon compression.At pressures P 13.7 GPa we observed the appearance of a resistance drop of as much as~50%around 70 K,which evolves into a kink-like anomaly at pressures above 40 GPa and shifts to lower temperatures gradually with increasing magnetic field.These observations are consistent with the recent report mentioned above.On the other hand,sample 2 measured in the CAC retains metallic behavior in the investigated pressure range up to 15 GPa.The hump-like anomaly in resistance around~130 K at ambient pressure disappears at P≥2 GPa.In the pressure range of 11–15 GPa we observed the gradual development of a shoulder-like anomaly in resistance at low temperatures,which evolves into a pronounced drop of resistance of 98%below 62 K at 15 GPa,reaching a temperature-independent resistance of 20μΩbelow 20 K.Similarly,this resistance anomaly can be progressively shifted to lower temperatures by applying external magnetic fields,resembling a typical superconducting transition.Measurements on sample 3 in the CAC reproduce the resistance drop at pressures above 10 GPa and realize zero resistance below 10 K at 15 GPa even though an unusual semiconducting-like behavior is retained in the normal state.Based on these results,we constructed a dome-shaped superconducting phase diagram and discuss some issues regarding the sample-dependent behaviors on pressure-induced hightemperature superconductivity in the La_(3)Ni_(2)O_(7)crystals.展开更多
基金the support from the National Key Research and Development Program of China(Grant No.2017YFA0302902)the support from the National Key Research and Development Program of China(Grant No.2022YFA1405400)+2 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0301902)the National Natural Science Foundation of China(Grant No.12274290)the Sponsorship from Yangyang Development Fund。
文摘High-T_(c)superconductivity with possible T_(c)≈80 K has been reported in the single crystal of La_(3)Ni_(2)O_(7)under high pressure.Based on the electronic structure given by the density functional theory calculations,we propose an effective bi-layer model Hamiltonian including both 3d_(z)^(2)and 3d_((x)^(2)-(y)^(2))orbital electrons of the nickel cations.The main feature of the model is that the 3d_(z)^(2)electrons form inter-layerσ-bonding and anti-bonding bands via the apical oxygen anions between the two layers,while the 3d_((x)^(2)-(y)^(2))electrons hybridize with the 3d_(z)^(2)electrons within each NiO_(2)plane.The chemical potential difference of these two orbital electrons ensures that the 3d_(z)^(2)orbitals are close to half-filling and the 3d_((x)^(2)-(y)^(2))orbitals are near quarter-filling.The strong on-site Hubbard repulsion of the 3d_(z)^(2)orbital electrons gives rise to an effective inter-layer antiferromagnetic spin super-exchange J.Applying pressure can self dope holes on the 3d_(z)^(2)orbitals with the same amount of electrons doped on the 3d_((x)^(2)-(y)^(2))orbitals.By performing numerical density-matrix renormalization group calculations on a minimum setup and focusing on the limit of large J and small doping of 3d_(z)^(2)orbitals,we find the superconducting instability on both the 3d_(z)^(2)and3d_((x)^(2)-(y)^(2))orbitals by calculating the equal-time spin singlet pair–pair correlation function.Our numerical results may provide useful insights in the high-T_(c)superconductivity in single crystal La_(3)Ni_(2)O_(7)under high pressure.
基金supported by the Beijing Natural Science Foundation(Grant No.Z190008)the National Key Research and Development Program of China(Grant Nos.2018YFA0305700 and 2021YFA1400200)+6 种基金the National Natural Science Foundation of China(Grant Nos.12025408,11921004,11834016,and 11888101)supported by the National Natural Science Foundation of China(Grant No.12174454)the Strategic Priority Research Program of CAS(Grant No.XDB33000000)CAS Project for Young Scientists in Basic Research(Grant Nos.2022YSBR-047 and 2022YSBR-048)the Users with Excellence Program of Hefei Science Center CAS(Grant No.2021HSCUE008)Guangdong Basic and Applied Basic Research Funds(Grant No.2021B1515120015)Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices(Grant No.2022B1212010008)。
文摘The recent report of pressure-induced structural transition and signature of superconductivity with T_(c)≈80 K above 14 GPa in La_(3)Ni_(2)O_(7)crystals has garnered considerable attention.To further elaborate this discovery,we carried out comprehensive resistance measurements on La_(3)Ni_(2)O_(7)crystals grown in an optical-image floating zone furnace under oxygen pressure(15 bar)using a diamond anvil cell(DAC)and cubic anvil cell(CAC),which employ a solid(KBr)and liquid(glycerol)pressure-transmitting medium,respectively.Sample 1 measured in the DAC exhibits a semiconducting-like behavior with large resistance at low pressures and gradually becomes metallic upon compression.At pressures P 13.7 GPa we observed the appearance of a resistance drop of as much as~50%around 70 K,which evolves into a kink-like anomaly at pressures above 40 GPa and shifts to lower temperatures gradually with increasing magnetic field.These observations are consistent with the recent report mentioned above.On the other hand,sample 2 measured in the CAC retains metallic behavior in the investigated pressure range up to 15 GPa.The hump-like anomaly in resistance around~130 K at ambient pressure disappears at P≥2 GPa.In the pressure range of 11–15 GPa we observed the gradual development of a shoulder-like anomaly in resistance at low temperatures,which evolves into a pronounced drop of resistance of 98%below 62 K at 15 GPa,reaching a temperature-independent resistance of 20μΩbelow 20 K.Similarly,this resistance anomaly can be progressively shifted to lower temperatures by applying external magnetic fields,resembling a typical superconducting transition.Measurements on sample 3 in the CAC reproduce the resistance drop at pressures above 10 GPa and realize zero resistance below 10 K at 15 GPa even though an unusual semiconducting-like behavior is retained in the normal state.Based on these results,we constructed a dome-shaped superconducting phase diagram and discuss some issues regarding the sample-dependent behaviors on pressure-induced hightemperature superconductivity in the La_(3)Ni_(2)O_(7)crystals.
基金Supported by the National Natural Science Foundation of China under Grant Nos 20121302227, 11120101003 and 11121063, and the China Postdoctoral Science Foundation under Grant No 2013M541069.
文摘在二维的 KondoHeisenberg 格子模型离开充满一半，联合的本地 antiferromagnetic 交换能经由屏蔽效果的 Kondo 提供 quasiparticles 的配对的机制，导致重费米子超导性。我们发现配对的对称强烈取决于费密表面(FS ) 处于正常金属性的状态的结构。什么时候 J <SUB > H </SUB>/J<SUB > K </SUB> 是很小的， FS 是在 Brillouin 地区的角落附近的一个小像洞的圆，并且配对对称的 s 波浪有一个更低的地面状态精力。为联合 J <SUB 的价值的中介 > H </SUB>/J<SUB > 配对对称的扩大 s 波浪给赞成地面状态的 K </SUB>, 。不管多么 J <SUB > H </SUB>/J<SUB > K </SUB> 比批评价值大， FS 转变成穿过磁性的 Brillouin 地区的边界的四个小洞衣袋，并且配对对称的 d 波浪变得更有利。在那政体，结果超导的状态被节的 d 波浪或无节点的 d 波浪状态描绘，取决于也充满因素的传导电子。连续阶段转变在这二个状态之间存在。这结果可能与到一个充分豁开的状态的节的 d 波浪状态的阶段转变有关，它最近在做 Yb 的 CeCoIn <SUB>5</SUB> 被观察了。
