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
Recently,competing electronic instabilities,including superconductivity and density-wave-like order,have been discovered in vanadium-based kagome metals AV_(3)Sb_(5)(A=K,Rb,Cs)with a nontrivial band topology.This find...Recently,competing electronic instabilities,including superconductivity and density-wave-like order,have been discovered in vanadium-based kagome metals AV_(3)Sb_(5)(A=K,Rb,Cs)with a nontrivial band topology.This finding stimulates considerable interest to study the interplay of these competing electronic orders and possible exotic excitations in the superconducting state.Here,we performed51V and133Cs nuclear magnetic resonance(NMR)measurements on a CsV_(3)Sb_(5)single crystal to clarify the nature of density-wave-like transition in these kagome superconductors.A first-order structural transition is unambiguously revealed below T_(s)~94 K by observing the sudden splitting of Knight shift in^(51)V NMR spectrum.Moreover,combined with^(133)Cs NMR spectrum,the present result confirms a three-dimensional structural modulation.By further analyzing the anisotropy of Knight shift and 1/T_(1)T at^(51)V nuclei,we proposed that the orbital order is the primary electronic order induced by the firstorder structural transition,which is supported by further analysis on electric field gradient at^(51)V nuclei.In addition,the evidence for possible orbital fluctuations is also revealed above T_(s).The present work sheds light on a rich orbital physics in kagome superconductors AV_(3)Sb_(5).展开更多
Revealing the role of Coulomb interaction in topological semimetals with Dirac/Weyl-like band dispersion shapes a new frontier in condensed matter physics.Topological node-line semimetals(TNLSMs),anticipated as a fert...Revealing the role of Coulomb interaction in topological semimetals with Dirac/Weyl-like band dispersion shapes a new frontier in condensed matter physics.Topological node-line semimetals(TNLSMs),anticipated as a fertile ground for exploring electronic correlation effects due to the anisotropy associated with their node-line structure,have recently attracted considerable attention.In this study,we report an experimental observation for correlation effects in TNLSMs realized by black phosphorus(BP)under hydrostatic pressure.By performing a combination of nuclear magnetic resonance measurements and band calculations on compressed BP,a magnetic-field-induced electronic instability of Weyl-like fermions is identified under an external magnetic field parallel to the so-called nodal ring in the reciprocal space.Anomalous spin fluctuations serving as the fingerprint of electronic instability are observed at low temperatures,and they are observed to maximize at approximately 1.0 GPa.This study presents compressed BP as a realistic material platform for exploring the rich physics in strongly coupled Weyl-like fermions.展开更多
The search of quantum spin liquid(QSL),an exotic magnetic state with strongly fluctuating and highly entangled spins down to zero temperature,is a main theme in current condensed matter physics.However,there is no smo...The search of quantum spin liquid(QSL),an exotic magnetic state with strongly fluctuating and highly entangled spins down to zero temperature,is a main theme in current condensed matter physics.However,there is no smoking gun evidence for deconfined spinons in any QSL candidate so far.The disorders and competing exchange interactions may prevent the formation of an ideal QSL state on frustrated spin lattices.Here we report comprehensive and systematic measurements of the magnetic susceptibility,ultralow-temperature specific heat,muon spin relaxation(μSR),nuclear magnetic resonance(NMR),and thermal conductivity for NaYbSe2 single crystals,in which Yb3+ions with effective spin-1/2 form a perfect triangular lattice.All these complementary techniques find no evidence of long-range magnetic order down to their respective base temperatures.Instead,specific heat,μSR,and NMR measurements suggest the coexistence of quasi-static and dynamic spins in NaYbSe2.The scattering from these quasi-static spins may cause the absence of magnetic thermal conductivity.Thus,we propose a scenario of fluctuating ferrimagnetic droplets immersed in a sea of QSL.This may be quite common on the way pursuing an ideal QSL,and provides a brand new platform to study how a QSL state survives impurities and coexists with other magnetically ordered states.展开更多
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supported by the National Key R&D Program of China(Grant Nos.2017YFA0303000,and 2016YFA0300201)the National Natural Science Foundation of China(Grant Nos.11888101,and 12034004)+2 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB25000000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000)the Collaborative Innovation Program of Hefei Science Center,CAS(Grant No.2019HSCCIP007)。
文摘Recently,competing electronic instabilities,including superconductivity and density-wave-like order,have been discovered in vanadium-based kagome metals AV_(3)Sb_(5)(A=K,Rb,Cs)with a nontrivial band topology.This finding stimulates considerable interest to study the interplay of these competing electronic orders and possible exotic excitations in the superconducting state.Here,we performed51V and133Cs nuclear magnetic resonance(NMR)measurements on a CsV_(3)Sb_(5)single crystal to clarify the nature of density-wave-like transition in these kagome superconductors.A first-order structural transition is unambiguously revealed below T_(s)~94 K by observing the sudden splitting of Knight shift in^(51)V NMR spectrum.Moreover,combined with^(133)Cs NMR spectrum,the present result confirms a three-dimensional structural modulation.By further analyzing the anisotropy of Knight shift and 1/T_(1)T at^(51)V nuclei,we proposed that the orbital order is the primary electronic order induced by the firstorder structural transition,which is supported by further analysis on electric field gradient at^(51)V nuclei.In addition,the evidence for possible orbital fluctuations is also revealed above T_(s).The present work sheds light on a rich orbital physics in kagome superconductors AV_(3)Sb_(5).
基金supported by the National Key R&D Program of the Ministry of Science and Technology of China(Grant Nos.2017YFA0300201,and 2016YFA0303000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000)+1 种基金the National Natural Science Foundation of China(Grant No.11534010)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences,China(Grant No.QYZDY-SSWSLH021)。
文摘Revealing the role of Coulomb interaction in topological semimetals with Dirac/Weyl-like band dispersion shapes a new frontier in condensed matter physics.Topological node-line semimetals(TNLSMs),anticipated as a fertile ground for exploring electronic correlation effects due to the anisotropy associated with their node-line structure,have recently attracted considerable attention.In this study,we report an experimental observation for correlation effects in TNLSMs realized by black phosphorus(BP)under hydrostatic pressure.By performing a combination of nuclear magnetic resonance measurements and band calculations on compressed BP,a magnetic-field-induced electronic instability of Weyl-like fermions is identified under an external magnetic field parallel to the so-called nodal ring in the reciprocal space.Anomalous spin fluctuations serving as the fingerprint of electronic instability are observed at low temperatures,and they are observed to maximize at approximately 1.0 GPa.This study presents compressed BP as a realistic material platform for exploring the rich physics in strongly coupled Weyl-like fermions.
基金National Key R&D Program of China(Grant No.2022YFA1402203)National Natural Science Foundation of China of China(Grant No.12034004,No.11774061,and No.11774306)+2 种基金Shanghai Municipal Science and Technology(Major Project Grant No.2019SHZDZX01,No.20ZR1405300,and No.23ZR1404500)Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB28000000)Innovation program for Quantum Science and Technology(Grant No.2021ZD0302500).
文摘The search of quantum spin liquid(QSL),an exotic magnetic state with strongly fluctuating and highly entangled spins down to zero temperature,is a main theme in current condensed matter physics.However,there is no smoking gun evidence for deconfined spinons in any QSL candidate so far.The disorders and competing exchange interactions may prevent the formation of an ideal QSL state on frustrated spin lattices.Here we report comprehensive and systematic measurements of the magnetic susceptibility,ultralow-temperature specific heat,muon spin relaxation(μSR),nuclear magnetic resonance(NMR),and thermal conductivity for NaYbSe2 single crystals,in which Yb3+ions with effective spin-1/2 form a perfect triangular lattice.All these complementary techniques find no evidence of long-range magnetic order down to their respective base temperatures.Instead,specific heat,μSR,and NMR measurements suggest the coexistence of quasi-static and dynamic spins in NaYbSe2.The scattering from these quasi-static spins may cause the absence of magnetic thermal conductivity.Thus,we propose a scenario of fluctuating ferrimagnetic droplets immersed in a sea of QSL.This may be quite common on the way pursuing an ideal QSL,and provides a brand new platform to study how a QSL state survives impurities and coexists with other magnetically ordered states.
