Elastic neutron diffraction measurements were performed on single crystals to study the ground state below the mysterious exotic transition temperature 0.86 K. An antiferromagnetic order with a tiny moment of 0.027 μ...Elastic neutron diffraction measurements were performed on single crystals to study the ground state below the mysterious exotic transition temperature 0.86 K. An antiferromagnetic order with a tiny moment of 0.027 μB per formula is formed as the ground state for CeOs4Sb12 below the transition point. Our neutron data gives the evidence of spin density wave state for CeOs4Sb12 in this work.展开更多
The recent discovery of superconductivity in La_(3)Ni_(2)O_(7-δ)with a transition temperature Tc close to 80 K at high pressures has attracted significant attention,due particularly to a possible density wave(DW)tran...The recent discovery of superconductivity in La_(3)Ni_(2)O_(7-δ)with a transition temperature Tc close to 80 K at high pressures has attracted significant attention,due particularly to a possible density wave(DW)transition occurring near the superconducting dome.Identifying the type of DW order is crucial for understanding the origin of superconductivity in this system.However,owing to the presence of La4Ni3O10 and other intergrowth phases in La_(3)Ni_(2)O_(7-δ)samples,extracting the intrinsic information from the La_(3)Ni_(2)O_(7) phase is challenging.In this study,we employed ^(139)La nuclear quadrupole resonance(NQR)measurements to eliminate the influence of other structural phases in the sample and obtain microscopic insights into the DW transition in La_(3)Ni_(2)O_(7-δ).Below the DW transition temperature T_(DW)∼153 K,we observe a distinct splitting in the±5/2↔±7/2 transition of the NQR resonance peak at the La(2)site,while only a line broadening is seen in the±3/2↔±5/2 transition peak.Through further analysis of the spectra,we show that the line splitting is due to a unidirectional charge modulation.A magnetic line broadening is also observed below T_(DW),accompanied by a large enhancement of the spin-lattice relaxation rate,indicating the formation of magnetically ordered moments in the DW state.Our results suggest a simultaneous formation of charge-and spin-density wave orders in La_(3)Ni_(2)O_(7-δ),thereby offering critical insights into the electronic correlations in Ni-based superconductors.展开更多
Recently,a signature of high-temperature superconductivity above the liquid nitrogen temperature(77 K)was reported for La_(3)Ni_(2)O_(7−δ) under pressure.This finding immediately stimulated intense interest in the po...Recently,a signature of high-temperature superconductivity above the liquid nitrogen temperature(77 K)was reported for La_(3)Ni_(2)O_(7−δ) under pressure.This finding immediately stimulated intense interest in the possible mechanism of high-Tc superconductivity in double-layer nickelates.Notably,the pressure-dependent phase diagram inferred from transport measurements indicates that the superconductivity under high pressure emerges from the suppression of density-wave-like order at ambient pressure,which is similar to high-temperature superconductors.Therefore,clarifying the exact nature of the density-wave-like transition is important for determining the superconducting mechanism in double-layer nickelates.Here,nuclear magnetic resonance(NMR)spectroscopy of 139La nuclei was performed to study the density-wave-like transition in a single crystal of La_(3)Ni_(2)O_(7−δ.)At high temperatures,two sets of sharp 139La NMR peaks are clearly distinguishable from a broad background signals,which are ascribed to La(1)sites from two bilayer Ruddlesden-Popper phases with different oxygen vacancyδ.As the temperature decreases,the temperature-dependent^(139)La NMR spectra and nuclear spin-lattice relaxation rate(1/T_(1))for both La(1)sites provide evidence of spin-density-wave(SDW)ordering below the transition temperature(T_(SDW)),which is approximately 150 K.The anisotropic splitting in the NMR spectra suggests the formation of a possible double spin stripe with magnetic moments aligned along the c-axis.Furthermore,we studied the pressure-dependent SDW transition up to∼2.7 GPa.Surprisingly,the TSDW inferred from NMR measurements of both La(1)sites increases with increasing pressure,which is opposite to the results from previous transport measurements under pressure and suggests an intriguing phase diagram between superconductivity and SDW.In contrast,the present^(139)La NMR is insensitive to the possible charge-density-wave(CDW)order in the Ni-O planes.All these results will be helpful for building a connection between superconductivity and magnetic interactions in double-layer nickelates.展开更多
In quasi-one-dimensional(q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase tr...In quasi-one-dimensional(q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic(AFM) compound YbAlO3, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations,and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave(LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.展开更多
Research on nickel-based superconductors has progressed from infinite-layer LaNiO_(2) to finite-layer La_(6)Ni_(5)O_(12),and most recently to the Ruddlesden-Popper phase La_(3)Ni_(2)O_(7),which was found to exhibit on...Research on nickel-based superconductors has progressed from infinite-layer LaNiO_(2) to finite-layer La_(6)Ni_(5)O_(12),and most recently to the Ruddlesden-Popper phase La_(3)Ni_(2)O_(7),which was found to exhibit onset of superconductivity at∼80K under a pressure of∼16 GPa.Using density functional calculations and multi-orbital,multi-atom cluster exact diagonalization that includes local exchange and Coulomb interactions,here we analyze the pressure dependent low-energy electronic states of the Ni_(2)O_(9) cluster,relevant for the bilayer phase of La_(3)Ni_(2)O_(7).We quantify the various possible spin states and the exchange and superexchange mechanisms of the Ni_(2)O_(9) cluster are quantified through the involvement of the Ni-3d_(3z^(2)−r^(2)) orbitals and the atomic Hund’s rule exchange,the apical bridging O-2pz orbitals,and the orbitals involved in the formation of local Zhang-Rice singlet like states.We find that the leading configurations contributing to the cluster ground-states both for nominal valence and also with local charge fluctuations,do not involve occupation of the apical oxygen;instead,they favor the formation of in-plane Zhang-Rice singlet-like states between an O ligand hole and the Ni 3d_(z^(2)−y^(2)) orbital.We also highlight two possible charge and spin ordered states suggested by our cluster results,that are nearly degenerate at all relevant pressures within our modeling.展开更多
Gamma-ray (GRBs) and X-ray Bursts are millisecond-10 and 1000 seconds-long events of unknown origin. Recent simulations of the merger of binary neutron star systems do not generate a magnetically dominated c...Gamma-ray (GRBs) and X-ray Bursts are millisecond-10 and 1000 seconds-long events of unknown origin. Recent simulations of the merger of binary neutron star systems do not generate a magnetically dominated called funnel nor a relativistic outflow. New models for the detection the afterglow of GRB 121024A, measured 0.15 days after the burst, invoke anisotropy as required to produce the complex microphysics of realistic shocks in relativistic jets. On the other hand the non-thermal gamma-rays are supposed to be produced by a fireball of relativistic e<sup>?</sup>e<sup>+</sup> pairs that are created by annihilation of neutrino-antineutrino pairs in the vicinity of the hot, merged object. It is also known that in a system of a large number of fermions with pairs, gravitational interaction occurs a spontaneous breaking of the vacuum spatial symmetry, accompanied by gravitational mass defect. If spherical symmetry is broken, as in the known case of the merger scenario where a rapidly rotating disk can be formed and material is pulled away from rotation axis by centrifugal forces, then a baryon-free funnel along the rotation axes may allow relativistic beam of γ’s and e<sup>?</sup>e<sup>+</sup> to escape. It might lead to matter ejection with Lorentz factors of ~10<sup>2</sup> - 103</sup> which are in the right range to enable copious gamma production during shock interaction with ambient interstellar gas. Here we show that the space rays generation mechanism on a method of direct transformation of intergalactic gamma-rays to the proton current on spin shock-waves ensure precise agreement between generated proton currents (spin shock waves theory) with the angular distribution data of Galactic gamma-rays as well as for the individual pulses of gamma-/X-ray bursts. There is a precise confirmation of the generated currents (theory) with the burst radiation data characterized by the standard deviation of ±1% in intensity in relative units within the sensitivity of the equipment. Thus, it was found that the spin angular momentum conservation law (equation of dynamics of spin shock waves) in the X-ray/gamma ranges is fulfilled exactly in real time. The next step involves setting the inverse problem of determining the wave function disturbance on the differential of measured smoothing pulses. In the asymptotic large times the problem is reduced to the solutions of the functional equation with shift of the argument. This will give additional information about the change speed of the wave, as well as on the interaction.展开更多
Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among th...Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).展开更多
文摘Elastic neutron diffraction measurements were performed on single crystals to study the ground state below the mysterious exotic transition temperature 0.86 K. An antiferromagnetic order with a tiny moment of 0.027 μB per formula is formed as the ground state for CeOs4Sb12 below the transition point. Our neutron data gives the evidence of spin density wave state for CeOs4Sb12 in this work.
基金supported by the National Key Research and Development Projects of China(Grant Nos.2023YFA1406103,2024YFA1611302,2024YFA1409200,and 2022YFA1403402)the National Natural Science Foundation of China(Grant Nos.12374142,12304170,12025408,12404179,and U23A6003)+2 种基金Beijing National Laboratory for Condensed Matter Physics(Grant No.2024BNLCMPKF005)the Chinese Academy of Sciences President’s International Fellowship Initiative(Grant No.2024PG0003)supported by the Synergetic Extreme Condition User Facility(SECUF,https://cstr.cn/31123.02.SECUF)。
文摘The recent discovery of superconductivity in La_(3)Ni_(2)O_(7-δ)with a transition temperature Tc close to 80 K at high pressures has attracted significant attention,due particularly to a possible density wave(DW)transition occurring near the superconducting dome.Identifying the type of DW order is crucial for understanding the origin of superconductivity in this system.However,owing to the presence of La4Ni3O10 and other intergrowth phases in La_(3)Ni_(2)O_(7-δ)samples,extracting the intrinsic information from the La_(3)Ni_(2)O_(7) phase is challenging.In this study,we employed ^(139)La nuclear quadrupole resonance(NQR)measurements to eliminate the influence of other structural phases in the sample and obtain microscopic insights into the DW transition in La_(3)Ni_(2)O_(7-δ).Below the DW transition temperature T_(DW)∼153 K,we observe a distinct splitting in the±5/2↔±7/2 transition of the NQR resonance peak at the La(2)site,while only a line broadening is seen in the±3/2↔±5/2 transition peak.Through further analysis of the spectra,we show that the line splitting is due to a unidirectional charge modulation.A magnetic line broadening is also observed below T_(DW),accompanied by a large enhancement of the spin-lattice relaxation rate,indicating the formation of magnetically ordered moments in the DW state.Our results suggest a simultaneous formation of charge-and spin-density wave orders in La_(3)Ni_(2)O_(7-δ),thereby offering critical insights into the electronic correlations in Ni-based superconductors.
基金support from the National Natural Science Foundation of China(523B2061)National Innovative Talents Program(GG2090007001)University of Science and Technology of China Startup Program(KY2090000044).
文摘Recently,a signature of high-temperature superconductivity above the liquid nitrogen temperature(77 K)was reported for La_(3)Ni_(2)O_(7−δ) under pressure.This finding immediately stimulated intense interest in the possible mechanism of high-Tc superconductivity in double-layer nickelates.Notably,the pressure-dependent phase diagram inferred from transport measurements indicates that the superconductivity under high pressure emerges from the suppression of density-wave-like order at ambient pressure,which is similar to high-temperature superconductors.Therefore,clarifying the exact nature of the density-wave-like transition is important for determining the superconducting mechanism in double-layer nickelates.Here,nuclear magnetic resonance(NMR)spectroscopy of 139La nuclei was performed to study the density-wave-like transition in a single crystal of La_(3)Ni_(2)O_(7−δ.)At high temperatures,two sets of sharp 139La NMR peaks are clearly distinguishable from a broad background signals,which are ascribed to La(1)sites from two bilayer Ruddlesden-Popper phases with different oxygen vacancyδ.As the temperature decreases,the temperature-dependent^(139)La NMR spectra and nuclear spin-lattice relaxation rate(1/T_(1))for both La(1)sites provide evidence of spin-density-wave(SDW)ordering below the transition temperature(T_(SDW)),which is approximately 150 K.The anisotropic splitting in the NMR spectra suggests the formation of a possible double spin stripe with magnetic moments aligned along the c-axis.Furthermore,we studied the pressure-dependent SDW transition up to∼2.7 GPa.Surprisingly,the TSDW inferred from NMR measurements of both La(1)sites increases with increasing pressure,which is opposite to the results from previous transport measurements under pressure and suggests an intriguing phase diagram between superconductivity and SDW.In contrast,the present^(139)La NMR is insensitive to the possible charge-density-wave(CDW)order in the Ni-O planes.All these results will be helpful for building a connection between superconductivity and magnetic interactions in double-layer nickelates.
基金Project supported by the National Natural Science Foundation of China(Grant No.11674392)the Ministry of Science and Technology of China,National Program on Key Research Project(Grant No.2016YFA0300504)the Research Funds of Remnin University of China(Grant No.18XNLG24).
文摘In quasi-one-dimensional(q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic(AFM) compound YbAlO3, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations,and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave(LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.
基金the support of the National Natural Science Foundation of China(Grant No.12174278)support from the National Natural Science Foundation of China(Grant No.12422407)+3 种基金the Startup Funding from Soochow Universitythe Priority Academic Program Development of Jiangsu Higher Education Institutionssupported by the Quantum Matter Institute(QMI)at the University of British Columbiathe Natural Sciences and Engineering Research Council of Canada(NSERC).
文摘Research on nickel-based superconductors has progressed from infinite-layer LaNiO_(2) to finite-layer La_(6)Ni_(5)O_(12),and most recently to the Ruddlesden-Popper phase La_(3)Ni_(2)O_(7),which was found to exhibit onset of superconductivity at∼80K under a pressure of∼16 GPa.Using density functional calculations and multi-orbital,multi-atom cluster exact diagonalization that includes local exchange and Coulomb interactions,here we analyze the pressure dependent low-energy electronic states of the Ni_(2)O_(9) cluster,relevant for the bilayer phase of La_(3)Ni_(2)O_(7).We quantify the various possible spin states and the exchange and superexchange mechanisms of the Ni_(2)O_(9) cluster are quantified through the involvement of the Ni-3d_(3z^(2)−r^(2)) orbitals and the atomic Hund’s rule exchange,the apical bridging O-2pz orbitals,and the orbitals involved in the formation of local Zhang-Rice singlet like states.We find that the leading configurations contributing to the cluster ground-states both for nominal valence and also with local charge fluctuations,do not involve occupation of the apical oxygen;instead,they favor the formation of in-plane Zhang-Rice singlet-like states between an O ligand hole and the Ni 3d_(z^(2)−y^(2)) orbital.We also highlight two possible charge and spin ordered states suggested by our cluster results,that are nearly degenerate at all relevant pressures within our modeling.
文摘Gamma-ray (GRBs) and X-ray Bursts are millisecond-10 and 1000 seconds-long events of unknown origin. Recent simulations of the merger of binary neutron star systems do not generate a magnetically dominated called funnel nor a relativistic outflow. New models for the detection the afterglow of GRB 121024A, measured 0.15 days after the burst, invoke anisotropy as required to produce the complex microphysics of realistic shocks in relativistic jets. On the other hand the non-thermal gamma-rays are supposed to be produced by a fireball of relativistic e<sup>?</sup>e<sup>+</sup> pairs that are created by annihilation of neutrino-antineutrino pairs in the vicinity of the hot, merged object. It is also known that in a system of a large number of fermions with pairs, gravitational interaction occurs a spontaneous breaking of the vacuum spatial symmetry, accompanied by gravitational mass defect. If spherical symmetry is broken, as in the known case of the merger scenario where a rapidly rotating disk can be formed and material is pulled away from rotation axis by centrifugal forces, then a baryon-free funnel along the rotation axes may allow relativistic beam of γ’s and e<sup>?</sup>e<sup>+</sup> to escape. It might lead to matter ejection with Lorentz factors of ~10<sup>2</sup> - 103</sup> which are in the right range to enable copious gamma production during shock interaction with ambient interstellar gas. Here we show that the space rays generation mechanism on a method of direct transformation of intergalactic gamma-rays to the proton current on spin shock-waves ensure precise agreement between generated proton currents (spin shock waves theory) with the angular distribution data of Galactic gamma-rays as well as for the individual pulses of gamma-/X-ray bursts. There is a precise confirmation of the generated currents (theory) with the burst radiation data characterized by the standard deviation of ±1% in intensity in relative units within the sensitivity of the equipment. Thus, it was found that the spin angular momentum conservation law (equation of dynamics of spin shock waves) in the X-ray/gamma ranges is fulfilled exactly in real time. The next step involves setting the inverse problem of determining the wave function disturbance on the differential of measured smoothing pulses. In the asymptotic large times the problem is reduced to the solutions of the functional equation with shift of the argument. This will give additional information about the change speed of the wave, as well as on the interaction.
基金supported by the National Nature Science Foundation of China[Grant Nos.92365204 and 12274298(Z.K.Liu)]the National Key R&D program of China[Grant No.2022YFA1604400/03(Z.K.Liu)]Zhangjiang Laboratory(Y.M.Zhang).The authors thank BL02B at the Shanghai Synchrotron Radiation Facility supported by the National Natural Science Foundation of China(Contract No.11227902).
文摘Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).
