Despite the recent discovery of superconductivity in Nd_(1-x)Sr_(x)NiO_(2) thin films,the absence of superconductivity and antiferromagnetism in their bulk materials remains a puzzle.Here we report the 1H NMR measurem...Despite the recent discovery of superconductivity in Nd_(1-x)Sr_(x)NiO_(2) thin films,the absence of superconductivity and antiferromagnetism in their bulk materials remains a puzzle.Here we report the 1H NMR measurements on powdered Nd0.85Sr0.15NiO2 samples by taking advantage of the enriched proton concentration after hydrogen annealing.We find a large full width at half maximum of the spectrum,which keeps increasing with decreasing the temperature T and exhibits an upturn behavior at low temperatures.The spin-lattice relaxation rate ^(1)T_(1)^(-1) is strongly enhanced when lowering the temperature,developing a broad peak at about 40 K,then decreases following a spin-wave-like behavior ^(1)T_(1)^(-1)∝T^(2) at lower temperatures.These results evidence a short-range glassy antiferromagnetic ordering of magnetic moments below 40 K and dominant antiferromagnetic fluctuations extending to much higher temperatures.Our findings reveal the strong electron correlations in bulk Nd_(0.85)Sr_(0.15)NiO_(2),and shed light on the mechanism of superconductivity observed in films of nickelates.展开更多
We utilize high-resolution resonant angle-resolved photoemission spectroscopy(ARPES)to study the band structure and hybridization effect of the heavy-fermion compound Ce2 IrIn8.We observe a nearly flat band at the bin...We utilize high-resolution resonant angle-resolved photoemission spectroscopy(ARPES)to study the band structure and hybridization effect of the heavy-fermion compound Ce2 IrIn8.We observe a nearly flat band at the binding energy of 7 meV below the coherent temperature Tcoh^40 K,which characterizes the electrical resistance maximum and indicates the onset temperature of hybridization.However,the Fermi vector and the Fermi surface volume have little change around Tcoh,which challenges the widely believed evolution from a hightemperature small Fermi surface to a low-temperature large Fermi surface.Our experimental results of the band structure fit well with the density functional theory plus dynamic mean-field theory calculations.展开更多
Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain...Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr1 _xBaxFel.97Nio.03As2, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Srl xBaxFe2As2 is determined by the strength of the magnetic-elastic coupling.展开更多
The recent discovery of superconductivity in the twisted bilayer graphene has stimulated numerous theoretical proposals concerning its exact gap symmetry.Among them, the d + id or p + ip-wave was believed to be the mo...The recent discovery of superconductivity in the twisted bilayer graphene has stimulated numerous theoretical proposals concerning its exact gap symmetry.Among them, the d + id or p + ip-wave was believed to be the most plausible solution.Here, considering that the superconductivity emerges near a correlated insulating state and may be induced by antiferromagnetic spin fluctuations, we apply the strong-coupling Eliashberg theory with both inter-and intraband quantum critical pairing interactions and discuss the possible gap symmetry in an effective low-energy four-orbital model.Our calculations reveal a nodeless s~±-wave as the most probable candidate for the superconducting gap symmetry in the experimentally relevant parameter range.This solution is distinctly different from previous theoretical proposals.It highlights the multi-gap nature of the superconductivity and puts the twisted bilayer graphene in the same class as the iron-pnictide,electron-doped cuprate, and some heavy fermion superconductors.展开更多
Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport pr...Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single- and poly-crystalline samples. The electrical resistivity p （T） is gradually enhanced by applying pressure over a wide temperature range from room temperature down to 25 mK. Two thermal activation gaps estimated from high- and low-temperature windows are found to increase with pressure. A flat p（T） observed at the lowest temperatures below 300 mK appears to be robust against both pressure and field. This feature as well as the increase of the energy gaps calls for more intensive investigations with respect to electron correlations and band topology.展开更多
基金Supported by the National Natural Science Foundation of China(Grant Nos.51872328,11674392,11774401,and A0402/11927809)the National Key R&D Program of China(Grant Nos.2016YFA0300504 and 2016YFA0300401)+2 种基金China Postdoctoral Science Foundation(Grant No.2020M680797)the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(Grant Nos.18XNLG24,20XNLG19,and 21XNLG18)。
文摘Despite the recent discovery of superconductivity in Nd_(1-x)Sr_(x)NiO_(2) thin films,the absence of superconductivity and antiferromagnetism in their bulk materials remains a puzzle.Here we report the 1H NMR measurements on powdered Nd0.85Sr0.15NiO2 samples by taking advantage of the enriched proton concentration after hydrogen annealing.We find a large full width at half maximum of the spectrum,which keeps increasing with decreasing the temperature T and exhibits an upturn behavior at low temperatures.The spin-lattice relaxation rate ^(1)T_(1)^(-1) is strongly enhanced when lowering the temperature,developing a broad peak at about 40 K,then decreases following a spin-wave-like behavior ^(1)T_(1)^(-1)∝T^(2) at lower temperatures.These results evidence a short-range glassy antiferromagnetic ordering of magnetic moments below 40 K and dominant antiferromagnetic fluctuations extending to much higher temperatures.Our findings reveal the strong electron correlations in bulk Nd_(0.85)Sr_(0.15)NiO_(2),and shed light on the mechanism of superconductivity observed in films of nickelates.
基金Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0401000,2015CB921300,2016YFA0300303,2016YFA0401002 and 2017YFA0303103the National Natural Science Foundation of China under Grant Nos 11674371,11774401 and 11874330+4 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences under Grant No XDB07000000the Beijing Municipal Science and Technology Commission under Grant No Z171100002017018the Hundred-Talent Program(type C)of the Chinese Academy of Sciencesthe Sino-Swiss Science and Technology Cooperation under Grant No IZLCZ2-170075the Swiss National Science Foundation under Grant No 200021-159678
文摘We utilize high-resolution resonant angle-resolved photoemission spectroscopy(ARPES)to study the band structure and hybridization effect of the heavy-fermion compound Ce2 IrIn8.We observe a nearly flat band at the binding energy of 7 meV below the coherent temperature Tcoh^40 K,which characterizes the electrical resistance maximum and indicates the onset temperature of hybridization.However,the Fermi vector and the Fermi surface volume have little change around Tcoh,which challenges the widely believed evolution from a hightemperature small Fermi surface to a low-temperature large Fermi surface.Our experimental results of the band structure fit well with the density functional theory plus dynamic mean-field theory calculations.
基金Project supported by the Science Fonds from the Ministry of Science and Technology of China(Grant Nos.2017YFA0302903,017YFA0303103,2016YFA0300502,and 2015CB921302)the National Natural Science Foundation of China(Grant Nos.11674406 and 11674372)+1 种基金the“Strategic Priority Research Program(B)”of the Chinese Academy of Sciences(Grant Nos.XDB07020300 and XDB07020200)the Youth Innovation Promotion Association of the Chinese Academy of Sciences
文摘Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr1 _xBaxFel.97Nio.03As2, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Srl xBaxFe2As2 is determined by the strength of the magnetic-elastic coupling.
基金Project supported by the National Key R&D Program of China(Grant No.2017YFA0303103)the National Natural Science Foundation of China(Grant Nos.11774401 and 11522435)+2 种基金the State Key Development Program for Basic Research of China(Grant No.2015CB921303)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB07020200)the Youth Innovation Promotion Association of the Chinese Academy of Sciences
文摘The recent discovery of superconductivity in the twisted bilayer graphene has stimulated numerous theoretical proposals concerning its exact gap symmetry.Among them, the d + id or p + ip-wave was believed to be the most plausible solution.Here, considering that the superconductivity emerges near a correlated insulating state and may be induced by antiferromagnetic spin fluctuations, we apply the strong-coupling Eliashberg theory with both inter-and intraband quantum critical pairing interactions and discuss the possible gap symmetry in an effective low-energy four-orbital model.Our calculations reveal a nodeless s~±-wave as the most probable candidate for the superconducting gap symmetry in the experimentally relevant parameter range.This solution is distinctly different from previous theoretical proposals.It highlights the multi-gap nature of the superconductivity and puts the twisted bilayer graphene in the same class as the iron-pnictide,electron-doped cuprate, and some heavy fermion superconductors.
基金Project supported by the Ministry of Science and Technology of China(Grant Nos.2015CB921303 and 2017YFA0303103)the National Natural Science Foundation of China(Grant Nos.11474332 and 11774404)the Chinese Academy of Sciences through the Strategic Priority Research Program(Grant No.XDB07020200)
文摘Kondo semimetal CeRu4Sn6 is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single- and poly-crystalline samples. The electrical resistivity p （T） is gradually enhanced by applying pressure over a wide temperature range from room temperature down to 25 mK. Two thermal activation gaps estimated from high- and low-temperature windows are found to increase with pressure. A flat p（T） observed at the lowest temperatures below 300 mK appears to be robust against both pressure and field. This feature as well as the increase of the energy gaps calls for more intensive investigations with respect to electron correlations and band topology.
