Three-dimensional quasi-direct numerical simulations have been performed to investigate a thermal plasma reactor with a counterflow jet. The effects of the momentum flux ratio and distance between the counterflow jet ...Three-dimensional quasi-direct numerical simulations have been performed to investigate a thermal plasma reactor with a counterflow jet. The effects of the momentum flux ratio and distance between the counterflow jet and the thermal plasma jet on the flow characteristics are addressed. The numerical results show that the dimensionless location of the stagnation layer is significantly affected by the momentum flux ratio, but it is not dependent on the distance.Specifically, the stagnation layer is closer to the plasma torch outlet with the increase of the momentum flux ratio. Furthermore, the flow regimes of the stagnation layer and the flow characteristics of the thermal plasma jet are closely related to the momentum flux ratio. The characteristic frequencies associated with the different regimes are identified. The deflecting oscillation flow regimes are found when the momentum flux ratio is low, which provokes axial velocity fluctuations inside the thermal plasma jet. By contrast, for cases with a high momentum flux ratio, flapping flow regimes are distinguished. The thermal plasma jets are very stable and the axial velocity fluctuations mainly exist in the stagnation layer.展开更多
Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolutio...Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolution of electronic structures associated with the change of lattice modulations is crucial for understanding of the CDW mechanism,with the combination of angle-resolved photoemission spectroscopy(ARPES)measurements and density functional theory calculations,we investigate how band dispersions change with the increase of lattice distortions.In particular,we focus on the electronic states around M point,where the van Hove singularities are expected to play crucial roles in the CDW transition.Previous ARPES studies reported a spectral weight splitting of the van Hove singularity around M point,which is associated with the 3D lattice modulations.Our studies reveal that this“splitting”can be connected to the two van Hove singularities at k_(z)=0 and k_(z)=π/c in the normal states.When the electronic system enters into the CDW state,both van Hove singularities move down.Such novel properties are important for understanding of the CDW transition.展开更多
The effects of the velocity and width in coflow argon jet inlet on the flow characteristics of laminar argon thermal plasma jet flowing into the cold air have been studied by the large eddy simulation methods. The Kel...The effects of the velocity and width in coflow argon jet inlet on the flow characteristics of laminar argon thermal plasma jet flowing into the cold air have been studied by the large eddy simulation methods. The Kelvin–Helmholtz instability between argon thermal plasma jet and coflow argon jet causes the transition from a laminar jet to a turbulent jet in the presence of coflow argon jet. Moreover, increasing the velocity and width in coflow argon jet inlet can enhance turbulent transport and provoke coherent structure in the downstream of thermal plasma jet. And the mixing characteristics between argon thermal plasma, coflow argon and ambient air are strengthened. In addition, the width in coflow argon jet inlet has a significant effect on the distribution of temperature in the upstream of thermal plasma jet. It was also found that the transition occurs in advance with the increase of velocity and width in coflow argon jet inlet.展开更多
Large eddy simulations based on the CFD software Open FOAM have been used to study the effect of Reynolds number and turbulence intensity on the flow and mixing characteristics of an argon thermal plasma jet.Detailed ...Large eddy simulations based on the CFD software Open FOAM have been used to study the effect of Reynolds number and turbulence intensity on the flow and mixing characteristics of an argon thermal plasma jet.Detailed analysis was carried out with respect to four aspects:the average flow field,the instantaneous flow field,turbulence statistical characteristics and the selfsimilarity.It was shown that for the argon thermal plasma jet with low Reynolds number,increasing the turbulence intensity will increase the turbulent transport mechanism in the mixing layer rather than in the jet axis,leading to the faster development of turbulence.The effect of the turbulent transport mechanism increases with increasing Reynolds number.However,the characteristics of flow and mixing are not affected by turbulence intensity for high Reynolds number situations.It was also found that the mean axial velocity and mean temperature in the axis of the turbulent thermal plasma jet satisfy the self-similarity aspects downstream.In addition,decay constant K is 1.25,which is much smaller than that(5.7-6.1)of the turbulent cold gas jet and has nothing to do with the Reynolds number or turbulence intensity in the jet inlet.展开更多
The superconducting ground state of kagome metals AV_(3)Sb_(5)(where A stands for K,Rb,or Cs)emerges from an exotic charge density wave(CDW)state that potentially breaks both rotational and time reversal symmetries.Ho...The superconducting ground state of kagome metals AV_(3)Sb_(5)(where A stands for K,Rb,or Cs)emerges from an exotic charge density wave(CDW)state that potentially breaks both rotational and time reversal symmetries.However,the specifics of the Cooper pairing mechanism,and the nature of the interplay between these two states remain elusive,largely due to the lack of momentum-space(k-space)superconducting energy gap structure.By implementing Bogoliubov quasiparticle interference(B QPI)imaging,we obtain k-space information on the multiband superconducting gap structureΔ_(SC)^(i)(k)in pristine CsV_(3)Sb_(5).We show that the estimated energy gap on the vanadium d_(xy/x^(2)-y^(2))orbital is anisotropic but nodeless,with a minimal value located near the M point.Interestingly,a comparison ofΔ_(SC)^(i)(k)with the CDW gapΔ_(CDW)^(i)(k)obtained by angle-re solved photoemission spectro scopy(ARPES)reveals direct k-space competition between the se two order parameters,i.e.,the opening of a large(small)CDW gap at a given momentum corresponds to a small(large)superconducting gap.When the long-range CDW order is suppressed by replacing vanadium with titanium,we find a nearly isotropic energy gap on both the V and Sb bands.This information will be critical for identifying the microscopic pairing mechanism and its interplay with intertwined electro nic orders in this kagome superconductor family.展开更多
The recent discovery of superconductivity(SC)and charge density wave(CDW)in kagome metals AV3Sb5(A=K,Rb,Cs)provides an ideal playground for the study of emergent electronic orders.Application of moderate pressure lead...The recent discovery of superconductivity(SC)and charge density wave(CDW)in kagome metals AV3Sb5(A=K,Rb,Cs)provides an ideal playground for the study of emergent electronic orders.Application of moderate pressure leads to a two-dome-shaped SC phase regime in CsV_(3)Sb_(5) accompanied by the destabilizing of CDW phase.Nonetheless,the nature of this pressure-tuned SC state and its interplay with the CDW are yet to be explored.Here,we perform soft point-contact spectroscopy(SPCS)measurements in CsV_(3)Sb_(5) to investigate the evolution of superconducting order parameter with pressure.Surprisingly,we find that the superconducting gap is significantly enhanced between the two SC domes,at which the zero-resistance temperature is suppressed and the transition is remarkably broadened.Moreover,the temperature-dependence of the SC gap in this pressure range severely deviates from the conventional Bardeen-Cooper-Schrieffer(BCS)behavior,evidencing for strong Cooper pair phase fluctuations.These findings reveal the complex intertwining of the CDW with SC in the compressed CsV_(3)Sb_(5),suggesting striking parallel to the cuprate superconductor La2xBaxCuO4.Our results point to the essential role of charge degree of freedom in the development of intertwining electronic orders,and thus provide new constraints for theories.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
Superconductivity beyond electron-phonon mechanism is always twisted with magnetism. Based on a new field-effect transistor with solid ion conductor as the gate dielectric(SIC-FET), we successfully achieve an electric...Superconductivity beyond electron-phonon mechanism is always twisted with magnetism. Based on a new field-effect transistor with solid ion conductor as the gate dielectric(SIC-FET), we successfully achieve an electric-field-controlled phase transition between superconductor and ferromagnetic insulator in(Li,Fe)OHFeSe. A dome-shaped superconducting phase with optimal T_c of 43K is continuously tuned into a ferromagnetic insulating phase, which exhibits an electric-field-controlled quantum critical behavior. The origin of the ferromagnetism is ascribed to the order of the interstitial Fe ions expelled from the(Li,Fe)OH layers by gating-controlled Li injection. These surprising findings offer a unique platform to study the relationship between superconductivity and ferromagnetism in Fe-based superconductors. This work also demonstrates the superior performance of the SIC-FET in regulating physical properties of layered unconventional superconductors.展开更多
Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit(ZT) in three-dimensional Dirac semimetal Cd_3As_2 crystal.It is found ...Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit(ZT) in three-dimensional Dirac semimetal Cd_3As_2 crystal.It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 T. The huge enhancement of ZT by magnetic field arises from the linear Dirac band with large Fermi velocity and the large electric thermal conductivity in Cd_3As_2. Our work paves a new way to greatly enhance the thermoelectric performance in the quantum topological materials.展开更多
Understanding the normal electronic state is crucial for unveiling the mechanism of unconventional superconductivity(SC). In this paper, by applying a magnetic field of up to 37T on FeSe single crystals, we could reve...Understanding the normal electronic state is crucial for unveiling the mechanism of unconventional superconductivity(SC). In this paper, by applying a magnetic field of up to 37T on FeSe single crystals, we could reveal the normal-state transport properties after SC was completely suppressed. The normal-state resistivity exhibited a Fermi liquid behavior at low temperatures. Large orbital magnetoresistance(MR) was observed in the nematic state with H//c, whereas MR was negligible with H//ab. The magnitude of the orbital MR showed an unusual reduction, and Kohler’s rule was severely violated below 10-25 K;these were attributable to spin fluctuations. The results indicated that spin fluctuations played a paramount role in the normalstate transport properties of FeSe albeit the Fermi liquid nature was at low temperature.展开更多
In 1929,Weyl H.proposed that the massless solution of the Dirac equation represents a pair of a new type of particles,the so-called Weyl fermions[1].However,their existence as a fundamental particle remains evasive af...In 1929,Weyl H.proposed that the massless solution of the Dirac equation represents a pair of a new type of particles,the so-called Weyl fermions[1].However,their existence as a fundamental particle remains evasive after more than eight decades.Neutrinos were once considered to be Weyl fermions until its mass was found.Recently,it was proposed that Weyl fermions can be hosted in a class of exotic condensed matter,so called Weyl semimetal(WSM),展开更多
The recently discovered kagome metal series AV3Sb5(A=K, Rb, Cs) exhibits topologically nontrivial band structures, chiral charge order and superconductivity, presenting a unique platform for realizing exotic electroni...The recently discovered kagome metal series AV3Sb5(A=K, Rb, Cs) exhibits topologically nontrivial band structures, chiral charge order and superconductivity, presenting a unique platform for realizing exotic electronic states. The nature of the superconducting state and the corresponding pairing symmetry are key questions that demand experimental clarification. Here, using a technique based on the tunneling diode oscillator, the magnetic penetration depth ?λ(T) of CsV3Sb5 was measured down to 0.07 K. A clear exponential behavior in ?λ(T) with marked deviations from a T or T2 temperature dependence was observed at low temperatures, indicating an absence of nodal quasiparticles. Temperature dependence of the superfiuid density and electronic specific heat can be described by two-gap s-wave superconductivity, consistent with the presence of multiple Fermi surfaces in CsV3Sb5. These results evidence nodeless superconductivity in CsV3Sb5 under ambient pressure, and constrain the allowed pairing symmetry.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
Phosphorus atomic chains, the narrowest nanostructures of black phosphorus (BP), are highly relevant to the in-depth development of BP-based one-dimensional (1D) nano-electronics components. In this study, we repo...Phosphorus atomic chains, the narrowest nanostructures of black phosphorus (BP), are highly relevant to the in-depth development of BP-based one-dimensional (1D) nano-electronics components. In this study, we report a top-down route for the preparation of phosphorus atomic chains via electron beam sculpturing inside a transmission electron microscope (TEM). The growth and dynamics (i.e., rupture and edge migration) of 1D phosphorus chains are experimentally captured for the first time. Furthermore, the dynamic behavior and associated energetics of the as-formed phosphorus chains are further investigated by density functional theory (DFT) calculations. It is hoped that these 1D BP structures will serve as a novel platform and inspire further exploration of the versatile properties of BP.展开更多
Different instabilities have been confirmed to exist in the three-dimensional(3D) electron gas when it is confined to the lowest Landau level in the extreme quantum limit. The recently discovered 3D topological semime...Different instabilities have been confirmed to exist in the three-dimensional(3D) electron gas when it is confined to the lowest Landau level in the extreme quantum limit. The recently discovered 3D topological semimetals offer a good platform to explore these phenomena due to the small sizes of their Fermi pockets, which means the quantum limit can be achieved at relatively low magnetic fields. In this work, we report the high-magnetic-field transport properties of the Dirac semimetal state in pressurized black phosphorus. Under applied hydrostatic pressure, the band structure of black phosphorus goes through an insulator-semimetal transition. In the high pressure topological semimetal phase, anomalous behaviors are observed on both magnetoresistance and Hall resistivity beyond the relatively low quantum limit field, which is demonstrated to indicate the emergence of an exotic electronic state hosting a density wave ordering. Our findings bring the first insight into the electronic interactions in black phosphorus under intense field.展开更多
By using scanning tunneling microscopy(STM)/spectroscopy(STS), we systematically characterize the electronic structure of lightly doped 1 T-TiSe_2, and demonstrate the existence of the electronic inhomogeneity and the...By using scanning tunneling microscopy(STM)/spectroscopy(STS), we systematically characterize the electronic structure of lightly doped 1 T-TiSe_2, and demonstrate the existence of the electronic inhomogeneity and the pseudogap state. It is found that the intercalation induced lattice distortion impacts the local band structure and reduce the size of the charge density wave(CDW) gap with the persisted 2 × 2 spatial modulation. On the other hand, the delocalized doping electrons promote the formation of pseudogap. Domination by either of the two effects results in the separation of two characteristic regions in real space, exhibiting rather different electronic structures. Further doping electrons to the surface confirms that the pseudogap may be the precursor for the superconducting gap. This study suggests that the competition of local lattice distortion and the delocalized doping effect contribute to the complicated relationship between charge density wave and superconductivity for intercalated 1 T-TiSe_2.展开更多
The thermoelectric effect refers to the phenomenon in which an electric voltage is directly generated from a temperature difference or vice versa.The two primary such effects are the Seebeck and the Peltier effects di...The thermoelectric effect refers to the phenomenon in which an electric voltage is directly generated from a temperature difference or vice versa.The two primary such effects are the Seebeck and the Peltier effects discovered in the early nineteenth century[1].These two effects provide the basis for functional thermoelectric devices,and are used to harvest electrical energy from waste heat or as solid-state Peltier cooler,see Figure 1(a).Here,the most challenging issue is to increase the thermoelectric figure of merit zT,which is determined by several interrelated material parameters including the Seebeck coefficient,the electrical and thermal conductivities,as well as the working temperature.展开更多
We made oligoamidine-based peptidomimetics highly specific for mycobacteria eradication by introducing and arraying lipophilic DNA binding motifs on macromolecular backbones.The short poly(amidino-phenylindole)(PAPI)s...We made oligoamidine-based peptidomimetics highly specific for mycobacteria eradication by introducing and arraying lipophilic DNA binding motifs on macromolecular backbones.The short poly(amidino-phenylindole)(PAPI)structures feature an alternating amphiphilic structure with cationic,lipophilic DNA-binding moieties,enabling fast and selective eradication of mycobacteria through binary,membrane-and DNA-selective mechanisms of action.More importantly,PAPIs address the primary treatment challenge by combating mycobacteria in eukaryotic cells and working as a sensitizer for conventional antibiotics,in bothways promoting more thorough removal of pathogens and reducing the mycobacteria’s resistance generation rate during treatment.Structural optimizationwas achieved to counter specific pathogens,including Mycobacterium tuberculosis,in the Mycobacterium genus.One of the hit peptidomimetics was evaluated in a zebrafish-based aquatic infection model using Mycobacterium fortuitum and a mice tail infection model using Mycobacterium marinum,both revealing excellent in vivo performance.展开更多
基金supported by National Natural Science Foundation of China (Nos. 12035015 and 12105282)。
文摘Three-dimensional quasi-direct numerical simulations have been performed to investigate a thermal plasma reactor with a counterflow jet. The effects of the momentum flux ratio and distance between the counterflow jet and the thermal plasma jet on the flow characteristics are addressed. The numerical results show that the dimensionless location of the stagnation layer is significantly affected by the momentum flux ratio, but it is not dependent on the distance.Specifically, the stagnation layer is closer to the plasma torch outlet with the increase of the momentum flux ratio. Furthermore, the flow regimes of the stagnation layer and the flow characteristics of the thermal plasma jet are closely related to the momentum flux ratio. The characteristic frequencies associated with the different regimes are identified. The deflecting oscillation flow regimes are found when the momentum flux ratio is low, which provokes axial velocity fluctuations inside the thermal plasma jet. By contrast, for cases with a high momentum flux ratio, flapping flow regimes are distinguished. The thermal plasma jets are very stable and the axial velocity fluctuations mainly exist in the stagnation layer.
基金supported by the National Key R&D Program of China (Grant No.2017YFA0402901)the National Natural Science Foundation of China (Grant No.U2032153)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.XDB25000000)the Users with Excellence Program of Hefei Science Center of the Chinese Academy of Sciences (Grant No.2021HSC-UE004)。
文摘Recently discovered kagome metals AV_(3)Sb_(5)(A=K,Rb,and Cs)provide an ideal platform to study the correlation among nontrivial band topology,unconventional charge density wave(CDW),and superconductivity.The evolution of electronic structures associated with the change of lattice modulations is crucial for understanding of the CDW mechanism,with the combination of angle-resolved photoemission spectroscopy(ARPES)measurements and density functional theory calculations,we investigate how band dispersions change with the increase of lattice distortions.In particular,we focus on the electronic states around M point,where the van Hove singularities are expected to play crucial roles in the CDW transition.Previous ARPES studies reported a spectral weight splitting of the van Hove singularity around M point,which is associated with the 3D lattice modulations.Our studies reveal that this“splitting”can be connected to the two van Hove singularities at k_(z)=0 and k_(z)=π/c in the normal states.When the electronic system enters into the CDW state,both van Hove singularities move down.Such novel properties are important for understanding of the CDW transition.
基金supported by National Natural Science Foundation of China(Nos.12035015 and 12105282)。
文摘The effects of the velocity and width in coflow argon jet inlet on the flow characteristics of laminar argon thermal plasma jet flowing into the cold air have been studied by the large eddy simulation methods. The Kelvin–Helmholtz instability between argon thermal plasma jet and coflow argon jet causes the transition from a laminar jet to a turbulent jet in the presence of coflow argon jet. Moreover, increasing the velocity and width in coflow argon jet inlet can enhance turbulent transport and provoke coherent structure in the downstream of thermal plasma jet. And the mixing characteristics between argon thermal plasma, coflow argon and ambient air are strengthened. In addition, the width in coflow argon jet inlet has a significant effect on the distribution of temperature in the upstream of thermal plasma jet. It was also found that the transition occurs in advance with the increase of velocity and width in coflow argon jet inlet.
基金supported by National Natural Science Foundation of China(No.12035015)。
文摘Large eddy simulations based on the CFD software Open FOAM have been used to study the effect of Reynolds number and turbulence intensity on the flow and mixing characteristics of an argon thermal plasma jet.Detailed analysis was carried out with respect to four aspects:the average flow field,the instantaneous flow field,turbulence statistical characteristics and the selfsimilarity.It was shown that for the argon thermal plasma jet with low Reynolds number,increasing the turbulence intensity will increase the turbulent transport mechanism in the mixing layer rather than in the jet axis,leading to the faster development of turbulence.The effect of the turbulent transport mechanism increases with increasing Reynolds number.However,the characteristics of flow and mixing are not affected by turbulence intensity for high Reynolds number situations.It was also found that the mean axial velocity and mean temperature in the axis of the turbulent thermal plasma jet satisfy the self-similarity aspects downstream.In addition,decay constant K is 1.25,which is much smaller than that(5.7-6.1)of the turbulent cold gas jet and has nothing to do with the Reynolds number or turbulence intensity in the jet inlet.
基金supported by the National Key R&D Program of China(Grant Nos.2022YFA1602600,and 2018YFA0305602)the National Natural Science Foundation of China(Grant Nos.11888101,12074364,52273309,and 52261135638)+5 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302802)the Basic Research Program of the Chinese Academy of Sciences Based on Major Scientific Infrastructures(Grant No.JZHKYPT-2021-08)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000)the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000012,and WK3510000015)the Major Basic Program of the Natural Science Foundation of Shandong Province(Grant No.ZR2021ZD01)。
文摘The superconducting ground state of kagome metals AV_(3)Sb_(5)(where A stands for K,Rb,or Cs)emerges from an exotic charge density wave(CDW)state that potentially breaks both rotational and time reversal symmetries.However,the specifics of the Cooper pairing mechanism,and the nature of the interplay between these two states remain elusive,largely due to the lack of momentum-space(k-space)superconducting energy gap structure.By implementing Bogoliubov quasiparticle interference(B QPI)imaging,we obtain k-space information on the multiband superconducting gap structureΔ_(SC)^(i)(k)in pristine CsV_(3)Sb_(5).We show that the estimated energy gap on the vanadium d_(xy/x^(2)-y^(2))orbital is anisotropic but nodeless,with a minimal value located near the M point.Interestingly,a comparison ofΔ_(SC)^(i)(k)with the CDW gapΔ_(CDW)^(i)(k)obtained by angle-re solved photoemission spectro scopy(ARPES)reveals direct k-space competition between the se two order parameters,i.e.,the opening of a large(small)CDW gap at a given momentum corresponds to a small(large)superconducting gap.When the long-range CDW order is suppressed by replacing vanadium with titanium,we find a nearly isotropic energy gap on both the V and Sb bands.This information will be critical for identifying the microscopic pairing mechanism and its interplay with intertwined electro nic orders in this kagome superconductor family.
基金supported by the National Natural Science Foundation of China(11888101 and 11534010)the National Key Research and Development Program of the Ministry of Science and Technology of China(2017YFA0303001 and 2019YFA0704900)+5 种基金the Anhui Initiative in Quantum Information Technologies(AHY160000)the Science Challenge Project of China(TZ2016004)the Key Research Program of Frontier Sciences,CAS,China(QYZDYSSWSLH021)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB25000000)the Collaborative Innovation Program of Hefei Science Center,CAS(2020HSC-CIP014)the Fundamental Research Funds for the Central Universities(WK3510000011).
文摘The recent discovery of superconductivity(SC)and charge density wave(CDW)in kagome metals AV3Sb5(A=K,Rb,Cs)provides an ideal playground for the study of emergent electronic orders.Application of moderate pressure leads to a two-dome-shaped SC phase regime in CsV_(3)Sb_(5) accompanied by the destabilizing of CDW phase.Nonetheless,the nature of this pressure-tuned SC state and its interplay with the CDW are yet to be explored.Here,we perform soft point-contact spectroscopy(SPCS)measurements in CsV_(3)Sb_(5) to investigate the evolution of superconducting order parameter with pressure.Surprisingly,we find that the superconducting gap is significantly enhanced between the two SC domes,at which the zero-resistance temperature is suppressed and the transition is remarkably broadened.Moreover,the temperature-dependence of the SC gap in this pressure range severely deviates from the conventional Bardeen-Cooper-Schrieffer(BCS)behavior,evidencing for strong Cooper pair phase fluctuations.These findings reveal the complex intertwining of the CDW with SC in the compressed CsV_(3)Sb_(5),suggesting striking parallel to the cuprate superconductor La2xBaxCuO4.Our results point to the essential role of charge degree of freedom in the development of intertwining electronic orders,and thus provide new constraints for theories.
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.
基金supported by the National Key R&D Program of China(2017YFA0303001 and 2016YFA0300201)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB25010100)+2 种基金the National Natural Science Foundation of China(11888101 and 11534010)Science Challenge Project(TZ2016004)Hefei Science Center CAS(2016HSC-IU001)
文摘Superconductivity beyond electron-phonon mechanism is always twisted with magnetism. Based on a new field-effect transistor with solid ion conductor as the gate dielectric(SIC-FET), we successfully achieve an electric-field-controlled phase transition between superconductor and ferromagnetic insulator in(Li,Fe)OHFeSe. A dome-shaped superconducting phase with optimal T_c of 43K is continuously tuned into a ferromagnetic insulating phase, which exhibits an electric-field-controlled quantum critical behavior. The origin of the ferromagnetism is ascribed to the order of the interstitial Fe ions expelled from the(Li,Fe)OH layers by gating-controlled Li injection. These surprising findings offer a unique platform to study the relationship between superconductivity and ferromagnetism in Fe-based superconductors. This work also demonstrates the superior performance of the SIC-FET in regulating physical properties of layered unconventional superconductors.
基金supported by the National Key R&D Program of the Ministry of Science and Technology China(2017YFA0303001,2016YFA0300201 and 2017YFA0204904)the National Natural Science Foundation of China(11534010,11774325 and21603210)+4 种基金the Key Research Program of Frontier Sciences CAS(QYZDY-SSW-SLH021)Hefei Science Center CAS(2016HSCIU001)the Fundamental Research Funds for the Central UniversitiesSupercomputing Center at USTC for providing the computing resourcespartially performed on the Superconducting Magnet and PPMS-16T Facilities,High Magnetic Field Laboratory of CAS
文摘Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit(ZT) in three-dimensional Dirac semimetal Cd_3As_2 crystal.It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 T. The huge enhancement of ZT by magnetic field arises from the linear Dirac band with large Fermi velocity and the large electric thermal conductivity in Cd_3As_2. Our work paves a new way to greatly enhance the thermoelectric performance in the quantum topological materials.
基金supported by the National Natural Science Foundation of China(Grant Nos.11888101,and 11534010)the National Key Research and Development Program of the Ministry of Science and Technology of China(Grant Nos.2019YFA0704900,2016YFA0300201,and 2017YFA0303001)+6 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(CAS)(Grant No.XDB25000000)Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000)the Science Challenge Project of China(Grant No.TZ2016004)the Key Research Program of Frontier SciencesCASChina(Grant No.QYZDYSSWSLH021)the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000011,and WK2030020031)。
文摘Understanding the normal electronic state is crucial for unveiling the mechanism of unconventional superconductivity(SC). In this paper, by applying a magnetic field of up to 37T on FeSe single crystals, we could reveal the normal-state transport properties after SC was completely suppressed. The normal-state resistivity exhibited a Fermi liquid behavior at low temperatures. Large orbital magnetoresistance(MR) was observed in the nematic state with H//c, whereas MR was negligible with H//ab. The magnitude of the orbital MR showed an unusual reduction, and Kohler’s rule was severely violated below 10-25 K;these were attributable to spin fluctuations. The results indicated that spin fluctuations played a paramount role in the normalstate transport properties of FeSe albeit the Fermi liquid nature was at low temperature.
文摘In 1929,Weyl H.proposed that the massless solution of the Dirac equation represents a pair of a new type of particles,the so-called Weyl fermions[1].However,their existence as a fundamental particle remains evasive after more than eight decades.Neutrinos were once considered to be Weyl fermions until its mass was found.Recently,it was proposed that Weyl fermions can be hosted in a class of exotic condensed matter,so called Weyl semimetal(WSM),
基金supported by the National Key R&D Program of China (Grant Nos. 2017YFA0303100, and 2016YFA0300202)Key R&D Program of Zhejiang Province, China (Grant No. 2021C01002)National Natural Science Foundation of China (Grant Nos. 11974306, and 12034017)。
文摘The recently discovered kagome metal series AV3Sb5(A=K, Rb, Cs) exhibits topologically nontrivial band structures, chiral charge order and superconductivity, presenting a unique platform for realizing exotic electronic states. The nature of the superconducting state and the corresponding pairing symmetry are key questions that demand experimental clarification. Here, using a technique based on the tunneling diode oscillator, the magnetic penetration depth ?λ(T) of CsV3Sb5 was measured down to 0.07 K. A clear exponential behavior in ?λ(T) with marked deviations from a T or T2 temperature dependence was observed at low temperatures, indicating an absence of nodal quasiparticles. Temperature dependence of the superfiuid density and electronic specific heat can be described by two-gap s-wave superconductivity, consistent with the presence of multiple Fermi surfaces in CsV3Sb5. These results evidence nodeless superconductivity in CsV3Sb5 under ambient pressure, and constrain the allowed pairing symmetry.
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Yihua Wang would like to acknowledge partial support by the Ministry of Science and Technology of China(2016YFA0301002 and 2017YFA0303000)the National Natural Science Foundation of China(11827805)+4 种基金Shanghai Municipal Science and Technology Major Project Da Jiang would like to acknowledge partial support by the‘‘Strategic Priority Research Program(B)”of the Chinese Academy of Sciences(XDB04040300)the National Natural Science Foundation of China(11274333)Hundred Talents Program of the Chinese Academy of Sciences.Shaoyu Yin would like to acknowledge support by the National Natural Science Foundation of China(11704072)Work at Stanford was supported by an NSF IMR-MIP(DMR-0957616)part of the National Nanotechnology Coordinated Infrastructure under award ECCS-1542152.
基金This work was financially supported by the National Natural Science Foundation of China (Nos. 51472215, 51222202, 91433103, 11274380, 11622437, 61674171, 11227403 and 11534010), the National Basic Research Program of China (Nos. 2014CB932500 and 2015CB21004), the 111 project (No. B16042) and the Fundamental Research Funds for the Central Universities (No. 16XNLQ01). J. S. Q. was supported by the Outstanding Innovative Talents Cultivation Funded Programs 2016 of Renmin University of China. This work made use of the resources of the Center of Electron Microscopy of Zhejiang University. Calculations were performed at the Physics Laboratory for High-Performance Computing of Renmin University of China and at the Shanghai Supercomputer Center. We thank Prof. Ray F. Egerton for fruitful discussions and Dr. Qiang Xu for his assistance on in situ heating.
文摘Phosphorus atomic chains, the narrowest nanostructures of black phosphorus (BP), are highly relevant to the in-depth development of BP-based one-dimensional (1D) nano-electronics components. In this study, we report a top-down route for the preparation of phosphorus atomic chains via electron beam sculpturing inside a transmission electron microscope (TEM). The growth and dynamics (i.e., rupture and edge migration) of 1D phosphorus chains are experimentally captured for the first time. Furthermore, the dynamic behavior and associated energetics of the as-formed phosphorus chains are further investigated by density functional theory (DFT) calculations. It is hoped that these 1D BP structures will serve as a novel platform and inspire further exploration of the versatile properties of BP.
基金supported by the National Natural Science Foundation of China (11534010, 11504378 and 11474287)the Key Research Program of Frontier Sciences, CAS, China (QYZDY-SSW-SLH021)+2 种基金the National Key R&D Program of the MOST of China (2016YFA0300201 and 2017YFA0303001)the Hefei Science Center, CAS (2016HSC-IU001)the Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology (2017FXCX001)
文摘Different instabilities have been confirmed to exist in the three-dimensional(3D) electron gas when it is confined to the lowest Landau level in the extreme quantum limit. The recently discovered 3D topological semimetals offer a good platform to explore these phenomena due to the small sizes of their Fermi pockets, which means the quantum limit can be achieved at relatively low magnetic fields. In this work, we report the high-magnetic-field transport properties of the Dirac semimetal state in pressurized black phosphorus. Under applied hydrostatic pressure, the band structure of black phosphorus goes through an insulator-semimetal transition. In the high pressure topological semimetal phase, anomalous behaviors are observed on both magnetoresistance and Hall resistivity beyond the relatively low quantum limit field, which is demonstrated to indicate the emergence of an exotic electronic state hosting a density wave ordering. Our findings bring the first insight into the electronic interactions in black phosphorus under intense field.
基金supported by the Ministry of Science and Technology of China(2014CB921103,2013CB922103,2016YFA0300400,2015CB921202)the National Natural Science Foundation of China(11774149,11374140,11190023,11774152,51372112,11574133)+1 种基金NSF Jiangsu Province(BK20150012)the Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics
文摘By using scanning tunneling microscopy(STM)/spectroscopy(STS), we systematically characterize the electronic structure of lightly doped 1 T-TiSe_2, and demonstrate the existence of the electronic inhomogeneity and the pseudogap state. It is found that the intercalation induced lattice distortion impacts the local band structure and reduce the size of the charge density wave(CDW) gap with the persisted 2 × 2 spatial modulation. On the other hand, the delocalized doping electrons promote the formation of pseudogap. Domination by either of the two effects results in the separation of two characteristic regions in real space, exhibiting rather different electronic structures. Further doping electrons to the surface confirms that the pseudogap may be the precursor for the superconducting gap. This study suggests that the competition of local lattice distortion and the delocalized doping effect contribute to the complicated relationship between charge density wave and superconductivity for intercalated 1 T-TiSe_2.
文摘The thermoelectric effect refers to the phenomenon in which an electric voltage is directly generated from a temperature difference or vice versa.The two primary such effects are the Seebeck and the Peltier effects discovered in the early nineteenth century[1].These two effects provide the basis for functional thermoelectric devices,and are used to harvest electrical energy from waste heat or as solid-state Peltier cooler,see Figure 1(a).Here,the most challenging issue is to increase the thermoelectric figure of merit zT,which is determined by several interrelated material parameters including the Seebeck coefficient,the electrical and thermal conductivities,as well as the working temperature.
基金This research was made possible as a result of the start-up funding from Hunan University,as a part of China’s Fundamental Research Funds for the Central Universities,the funding from the National Natural Science Foundation of China(grant nos.21877033,92163127,Y.B.,21807031,22177031,X.F.)the funding from the Natural Science Foundation of Hunan Province(grant no.2021JJ30088,Y.B.,2020JJ4177,X.F.)the Open Funding Project of the State Key Laboratory of Biocatalysis and Enzyme Engineering(Hubei University,SKLBEE2019003,X.F.).
文摘We made oligoamidine-based peptidomimetics highly specific for mycobacteria eradication by introducing and arraying lipophilic DNA binding motifs on macromolecular backbones.The short poly(amidino-phenylindole)(PAPI)structures feature an alternating amphiphilic structure with cationic,lipophilic DNA-binding moieties,enabling fast and selective eradication of mycobacteria through binary,membrane-and DNA-selective mechanisms of action.More importantly,PAPIs address the primary treatment challenge by combating mycobacteria in eukaryotic cells and working as a sensitizer for conventional antibiotics,in bothways promoting more thorough removal of pathogens and reducing the mycobacteria’s resistance generation rate during treatment.Structural optimizationwas achieved to counter specific pathogens,including Mycobacterium tuberculosis,in the Mycobacterium genus.One of the hit peptidomimetics was evaluated in a zebrafish-based aquatic infection model using Mycobacterium fortuitum and a mice tail infection model using Mycobacterium marinum,both revealing excellent in vivo performance.