The newly discovered superconductivity in infinite-layer nickelate superconducting films has attracted much attention,largely because their crystalline and electronic structures are similar to those of high-T_(c) cupr...The newly discovered superconductivity in infinite-layer nickelate superconducting films has attracted much attention,largely because their crystalline and electronic structures are similar to those of high-T_(c) cuprate superconductors.The upper critical field can provide a great deal of information on the subject of superconductivity,but detailed experimental data are still lacking for these films.We present the temperature-and angle-dependence of resistivity,measured under different magnetic fields H in Nd_(0.8)Sr_(0.2)NiO_(2) thin films.The onset superconducting transition occurs at about 16.2 K at 0 T.Temperature-dependent upper critical fields,determined using a criterion very close to the onset transition,show a clear negative curvature near the critical transition temperature,which can be explained as a consequence of the paramagnetically limited effect on superconductivity.The temperaturedependent anisotropy of the upper critical field is obtained from resistivity data,which yields a value decreasing from 3 to 1.2 with a reduction in temperature.This can be explained in terms of the variable contribution from the orbital limit effect on the upper critical field.The angle-dependence of resistivity at a fixed temperature,and at different magnetic fields,cannot be scaled to a curve,which deviates from the prediction of the anisotropic Ginzburg-Landau theory.However,at low temperatures,the resistance difference can be scaled via the parameter H^(β)| cos θ|(β=6-1),with θ being the angle enclosed between the c-axis and the applied magnetic field.As the first detailed study of the upper critical field of nickelate thin films,our results clearly indicate a small anisotropy,and a paramagnetically limited effect,in terms of superconductivity,in nickelate superconductors.展开更多
We perform ^(23)Na nuclear magnetic resonance(NMR) and magnetization measurements on an S=1,quasi-2D honeycomb lattice antiferromagnet Na_(3)Ni_(2)BiO_(6).A large positive Curie-Weiss constant of 22.9 K is observed.Th...We perform ^(23)Na nuclear magnetic resonance(NMR) and magnetization measurements on an S=1,quasi-2D honeycomb lattice antiferromagnet Na_(3)Ni_(2)BiO_(6).A large positive Curie-Weiss constant of 22.9 K is observed.The NMR spectra at low fields are consistent with a zigzag magnetic order,indicating a large easy-axis anisotropy.With the field applied along the c*axis,the NMR spectra confirm the existence of a 1/3-magnetization plateau phase between 5.1 T and 7.1 T.The transition from the zigzag order to the 1/3-magnetization plateau phase is also found to be a first-order type.A monotonic decrease of the spin gap is revealed in the 1/3-magnetization plateau phase,which reaches zero at a quantum critical field H_(C)≈8.35 T before entering the fully polarized phase.These data suggest the existence of exchange frustration in the system along with strong ferromagnetic interactions,hosting the possibility for Kitaev physics.Besides,well below the ordered phase,the 1/T_(1) at high fields shows either a level off or an enhancement upon cooling below 3 K,which suggests the existence of low-energy fluctuations.展开更多
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 report protonation in several compounds by an ionic-liquid-gating method, under optimized gating conditions.This leads to single superconducting phases for several compounds. Non-volatility of protons allows post-g...We report protonation in several compounds by an ionic-liquid-gating method, under optimized gating conditions.This leads to single superconducting phases for several compounds. Non-volatility of protons allows post-gating magnetization and transport measurements. The superconducting transition temperature Tc is enhanced to 43.5 K for FeSe0.93S0.07, and 41 K for Fe Se after protonation. Superconducting transitions with Tc^15 K for ZrNCl,~7.2 K for 1-TaS2, and ~3.8 K for Bi2Se3 are induced after protonation. Electric transport in protonated FeSe0.93S0.07 confirms high-temperature superconductivity. Our ^1H nuclear magnetic resonance(NMR)measurements on protonated Fe Se1-xSx reveal enhanced spin-lattice relaxation rate 1/^1T1 with increasing x,which is consistent with the LDA calculations that H+ is located in the interstitial sites close to the anions.展开更多
The electronic properties of TiO2-terminated BaTiO3（001） surface subjected to biaxial strain have been studied using first-principles calculations based on density functional theory. The Ti ions are always inward s...The electronic properties of TiO2-terminated BaTiO3（001） surface subjected to biaxial strain have been studied using first-principles calculations based on density functional theory. The Ti ions are always inward shifted either at compressive or tension strains, while the inward shift of the Ba ions occurs only for high compressive strain, implying an enhanced electric dipole moment in the case of high compressive strain. In particular, an insulator–metal transition is predicted at a compressive biaxial strain of 0.0475. These changes present a very interesting possibility for engineering the electronic properties of ferroelectric BaTiO3（001） surface.展开更多
基金the National Key R&D Program of China(Grant Nos.2016YFA0300401 and 2018YFA0704202)the National Natural Science Foundation of China(Grant Nos.12061131001,11774153,and 1861161004)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)the Fundamental Research Funds for the Central Universities(Grant No.0213-14380167)。
文摘The newly discovered superconductivity in infinite-layer nickelate superconducting films has attracted much attention,largely because their crystalline and electronic structures are similar to those of high-T_(c) cuprate superconductors.The upper critical field can provide a great deal of information on the subject of superconductivity,but detailed experimental data are still lacking for these films.We present the temperature-and angle-dependence of resistivity,measured under different magnetic fields H in Nd_(0.8)Sr_(0.2)NiO_(2) thin films.The onset superconducting transition occurs at about 16.2 K at 0 T.Temperature-dependent upper critical fields,determined using a criterion very close to the onset transition,show a clear negative curvature near the critical transition temperature,which can be explained as a consequence of the paramagnetically limited effect on superconductivity.The temperaturedependent anisotropy of the upper critical field is obtained from resistivity data,which yields a value decreasing from 3 to 1.2 with a reduction in temperature.This can be explained in terms of the variable contribution from the orbital limit effect on the upper critical field.The angle-dependence of resistivity at a fixed temperature,and at different magnetic fields,cannot be scaled to a curve,which deviates from the prediction of the anisotropic Ginzburg-Landau theory.However,at low temperatures,the resistance difference can be scaled via the parameter H^(β)| cos θ|(β=6-1),with θ being the angle enclosed between the c-axis and the applied magnetic field.As the first detailed study of the upper critical field of nickelate thin films,our results clearly indicate a small anisotropy,and a paramagnetically limited effect,in terms of superconductivity,in nickelate superconductors.
基金Project supported by the National Key R&D Program of China (Grant Nos. 2023YFA1406500, 2022YFA1402700, and 2021YFA1400400)the National Natural Science Foundation of China (Grant Nos. 12134020, 12374156, 12104503,12061131004, 12225407, and 12074174)。
文摘We perform ^(23)Na nuclear magnetic resonance(NMR) and magnetization measurements on an S=1,quasi-2D honeycomb lattice antiferromagnet Na_(3)Ni_(2)BiO_(6).A large positive Curie-Weiss constant of 22.9 K is observed.The NMR spectra at low fields are consistent with a zigzag magnetic order,indicating a large easy-axis anisotropy.With the field applied along the c*axis,the NMR spectra confirm the existence of a 1/3-magnetization plateau phase between 5.1 T and 7.1 T.The transition from the zigzag order to the 1/3-magnetization plateau phase is also found to be a first-order type.A monotonic decrease of the spin gap is revealed in the 1/3-magnetization plateau phase,which reaches zero at a quantum critical field H_(C)≈8.35 T before entering the fully polarized phase.These data suggest the existence of exchange frustration in the system along with strong ferromagnetic interactions,hosting the possibility for Kitaev physics.Besides,well below the ordered phase,the 1/T_(1) at high fields shows either a level off or an enhancement upon cooling below 3 K,which suggests the existence of low-energy fluctuations.
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 Natural Science Foundation of China under Grant Nos 51872328,11622437,11574394,11774423 and 11822412the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB30000000+5 种基金the Ministry of Science and Technology of China under Grant No 2016YFA0300504the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(RUC)(15XNLQ07,18XNLG14,19XNLG17)supported by the National Natural Science Foundation of China under Grant Nos 11774007 and U1832214supported by the Outstanding Innovative Talents Cultivation Funded Programs 2018 of Renmin University of Chinasupported by the U.S. Department of Energy,Office of Science,Basic Energy Sciences,Division of Materials Sciences and Engineering
文摘We report protonation in several compounds by an ionic-liquid-gating method, under optimized gating conditions.This leads to single superconducting phases for several compounds. Non-volatility of protons allows post-gating magnetization and transport measurements. The superconducting transition temperature Tc is enhanced to 43.5 K for FeSe0.93S0.07, and 41 K for Fe Se after protonation. Superconducting transitions with Tc^15 K for ZrNCl,~7.2 K for 1-TaS2, and ~3.8 K for Bi2Se3 are induced after protonation. Electric transport in protonated FeSe0.93S0.07 confirms high-temperature superconductivity. Our ^1H nuclear magnetic resonance(NMR)measurements on protonated Fe Se1-xSx reveal enhanced spin-lattice relaxation rate 1/^1T1 with increasing x,which is consistent with the LDA calculations that H+ is located in the interstitial sites close to the anions.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.1574091,51272078,and 51431006)the Natural Science Foundation of Guangdong Province of China(Grant No.2015A030313375)+1 种基金the Science and Technology Planning Project of Guangdong Province of China(Grant No.2015B090927006)the Program for International Innovation Cooperation Platform of Guangzhou City,China(Grant No.2014J4500016)
文摘The electronic properties of TiO2-terminated BaTiO3（001） surface subjected to biaxial strain have been studied using first-principles calculations based on density functional theory. The Ti ions are always inward shifted either at compressive or tension strains, while the inward shift of the Ba ions occurs only for high compressive strain, implying an enhanced electric dipole moment in the case of high compressive strain. In particular, an insulator–metal transition is predicted at a compressive biaxial strain of 0.0475. These changes present a very interesting possibility for engineering the electronic properties of ferroelectric BaTiO3（001） surface.
