Topological superconductor islands are thought to be the building blocks of topological quantum bits.We produced single-crystalline VSi_(x)islands with well-defined side facets and island size more than 200nm using mo...Topological superconductor islands are thought to be the building blocks of topological quantum bits.We produced single-crystalline VSi_(x)islands with well-defined side facets and island size more than 200nm using molecular beam epitaxy on Si substrate heated to 950℃throughout the growth process.By means of scanning tunneling spectroscopy,we revealed dynamical Coulomb blockade and superconductivity on isolated islands and on islands being connected by superconducting wetting layer respectively.Bi_(2)Te_(3)films were further deposited on VSi_(x)islands.Robust and homogenous proximity effect induced superconductivity was observed on various facets of the Bi_(2)Te_(3)/VSi_(x)hetero-nanostructure.Furthermore,our high-resolution spectroscopy identified Bosonic mode excitations on the topological superconductor islands.These results may establish a playground for the vortex Majorana islands.展开更多
Iron-based superconductors(FeSCs)feature a complex phase diagram,and their diverse cleavage terminations offer a versatile platform for modulating surface electronic states and investigating the underlying superconduc...Iron-based superconductors(FeSCs)feature a complex phase diagram,and their diverse cleavage terminations offer a versatile platform for modulating surface electronic states and investigating the underlying superconducting mechanisms.In this study,we explore the surface modulation of KCa_(2)Fe_(4)As_(4)F_(2)using scanning tunneling microscopy/spectroscopy.Cryogenically cleaved surfaces reveal multiple configurations,including√2×√2 reconstruction,1×2 and 1×3 stripes,as well as nanoscale vacancies.Reducing potassium coverage induces hole doping,which shifts the density of states peak toward the Fermi level and suppresses the superconducting gap from 4.8 meV to 3.2 meV.This behavior is reminiscent of the Van Hove singularity observed in hole-doped 122-type FeSCs.The band structure does not undergo a simple rigid shift,and the evolution of superconductivity can be attributed to the interplay between surface carriers and electronic correlations.Additionally,a V-shaped gap is observed at a unique location preserving the FeAs bilayer structure,where interlayer coupling effects are likely involved.The diversity of surface structures and electronic states in K12442 enhances our understanding of FeSCs and facilitates the modulation and application of FeAs superconducting layers.展开更多
Exploring novel superconductors is a crucial topic in condensed matter physics.There are few reports on the superconductivity of fluorine due to the extremely high pressures required for its metallization.Here,metalli...Exploring novel superconductors is a crucial topic in condensed matter physics.There are few reports on the superconductivity of fluorine due to the extremely high pressures required for its metallization.Here,metallization and superconductivity of fluorine were achieved in MgF_(5)at 120 GPa by exploiting the high-pressure s-d transition of doped Mg.The unexpected Mg-F covalent bonding induced by Mg-d and F-p orbital interactions led to fluorine metallization and the formation of an F skeleton similar to a H-cage.The high density of states(DOS)from the F skeleton and phonon softening from strong Fermi surface nesting contribute to a high superconducting transition temperature(Tc).The Tc of Pmmm-MgF_(5)at 120 GPa is 14.02 K,with strong electron-phonon coupling(λ=0.84),which is close to that of Li_(6)P at 270 GPa(λ=1.01).This is the first observation of superconductivity in main-group metal fluorides.Additionally,two near-monatomic F atoms exist in the interstitial region of MgF_(5),significantly enhancing electron-phonon coupling.This work challenges the traditional view of main-group metal fluorides and provides deeper insights into the superconductivity and physicochemical properties of fluorine.展开更多
Large-grain REBa_(2)Cu_(3)O_(7-δ)(REBCO,RE=rare earth)bulk superconductors offer promising magnetic field trapping capabilities due to their high critical current density,making them ideal for many important applicat...Large-grain REBa_(2)Cu_(3)O_(7-δ)(REBCO,RE=rare earth)bulk superconductors offer promising magnetic field trapping capabilities due to their high critical current density,making them ideal for many important applications such as trapped field magnets.However,for such large-grain superconductor bulks,there are lots of voids and cracks forming during the process of melting preparation,and some of them can be up to hundreds of microns or even millimeters in size.Consequently,these larger size voids/cracks pose a great threat to the strength of the bulks due to the inherent brittleness of superconductor REBCO materials.In order to ensure the operational safety of related superconducting devices with bulk superconductors,it is firstly important to accurately detect these voids/cracks in them.In this paper,we proposed a method for quantitatively evaluating multiple voids/cracks in bulk superconductors through the magnetic field and displacement response signals at superconductor bulk surface.The proposed method utilizes a damage index constructed from the magnetic field signals and displacement responses to identify the number and preliminary location of multiple defects.By dividing the detection area into subdomains and combining the magnetic field signals with displacement responses within each subdomain,a particle swarm algorithm was employed to evaluate the location and size parameters of the defects.In contrast to other evaluation methods using only magnetic field or displacement response signals,the combined evaluation method using both signals can identify the number of cracks effectively.Numerical studies demonstrate that the morphology of voids and cracks reconstructed using the proposed algorithm ideally matches real defects and is applicable to cases where voids and cracks coexist.This study provides a theoretical basis for the quantitative detection of voids/cracks in bulk superconductors.展开更多
Compared to traditional superhard materials with high electron density and short,strong covalent bonds,alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness.B...Compared to traditional superhard materials with high electron density and short,strong covalent bonds,alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness.Breaking through the limits of alloy materials is a preface and long-term topic,which is of great significance and value for improving the comprehensive mechanical properties of alloy materials.Here,we report on the discovery of a cubic alloy semiconducting material Ti_(2)Co with a large Vickers of hardness K_(v)^(exp)∼6.7GPa and low fracture toughness of K_(IC)^(exp)∼1.51MPa·m^(1/2).Unexpectedly,the K_(v)^(exp)∼6.7GPa is nearly triple of the K_(v)^(cal)∼2.66GPa predicted by density functional theory(DFT)calculations and theK_(IC)^(exp)∼1.51MPa·m^(1/2)is about one or two orders of magnitude smaller than that of ordinary titanium alloy materials(K_(IC)^(exp)∼30-120MPa·m^(1/2)).These specifications place Ti_(2)Co far from the phase space of the known alloy materials.Upon incorporation of oxygen into structural void positions,both values were simultaneously improved for Ti_(4)Co_(2)O to∼9.7GPa and∼2.19MPa·m^(1/2),respectively.Further DFT calculations on the electron localization function of Ti_(4)Co_(2)X(X=B,C,N,O)vs.the interstitial elements indicate that these simultaneous improvements originate from the coexistence of Ti-Co metallic bonds,the emergence of newly oriented Ti-X covalent bonds,and the increase of electron concentration.Moreover,the large difference between K_(v)^(exp)and K_(v)^(cal)of Ti_(2)Co suggests underlying mechanism concerning the absence of the O(16d)or Ti_(2)-O bonds in the O-(Ti_(2))_(6) octahedron.This discovery proposes a new pathway to simultaneously improve the comprehensive mechanical performances and illuminates the path of exploring superconducting materials with excellent mechanical performances.展开更多
The discovery of new superconducting materials,particularly those exhibiting high critical temperature(Tc),has been a vibrant area of study within the field of condensed matter physics.Conventional approaches primaril...The discovery of new superconducting materials,particularly those exhibiting high critical temperature(Tc),has been a vibrant area of study within the field of condensed matter physics.Conventional approaches primarily rely on physical intuition to search for potential superconductors within the existing databases.However,the known materials only scratch the surface of the extensive array of possibilities within the realm of materials.展开更多
The interplay between 2a_(0)×2a_(0)charge density wave(CDW),nematicity and superconductivity in AV_(3)Sb_(5)(A=K,Rb,Cs)compounds gives rise to a rich landscape of intriguing physical phenomena.In addition to the ...The interplay between 2a_(0)×2a_(0)charge density wave(CDW),nematicity and superconductivity in AV_(3)Sb_(5)(A=K,Rb,Cs)compounds gives rise to a rich landscape of intriguing physical phenomena.In addition to the 2a_(0)×2a_(0)CDW,a unidirectional 4a_(0)stripe CDW is also observed on the Sb surface of RbV3Sb5and CsV3Sb5.However,reports of stripe-like CDWs in KV3Sb5have been limited.Here,we report the first observation of a long-range unidirectional stripe order with a 6a_(0)modulation period on the Sb surface of KV_(3)Sb_(5),coexisting with the 2a_(0)×2a_(0)CDW.Notably,the intensity of the6a_(0)stripes in STM topographies exhibits pronounced contrast reversal between opposite bias voltages.Additionally,the wave vector of the 6a_(0)modulation shows no energy-dependent dispersion,confirming its CDW origin.Furthermore,the6a_(0)CDW is robust under a 7 T out-of-plane magnetic field and persists over a temperature range from 215 mK to 720 mK.These results provide compelling evidence for the emergence of a long-range unidirectional CDW in KV_(3)Sb_(5).展开更多
The kagome lattice,naturally encompassing Dirac fermions,flat bands,and van Hove singularities,tends to intertwine exotic electronic states.Revealing the characteristics of its Fermi surface will help clarify the natu...The kagome lattice,naturally encompassing Dirac fermions,flat bands,and van Hove singularities,tends to intertwine exotic electronic states.Revealing the characteristics of its Fermi surface will help clarify the nature of the complex quantum phenomena in kagome material.Here we report the Fermi surface properties of the novel kagome metal CsTi_(3)Bi_(5)by the de Haas-van Alphen oscillations.The observed oscillations are clear and consist of six principal frequencies ranging from 214 T to 1013 T.The angular dependence of the frequency implies a quasi-two-dimensional electronic structure.In addition,the geometry phase corresponding to 281 T,determined by direct Lifshitz-Kosevich formula fitting,yields a value close toπ,which may indicate a band structure with nontrivial topological property.These results underscore the potential of CsTi_(3)Bi_(5)as a promising platform to explore the interplay between topological order,electronic nematicity,and superconductivity.展开更多
The high-entropy alloy(HEA)superconductor,Ta_(1/6)Nb_(2/6)Hf_(1/6)Zr_(1/6)Ti_(1/6)(Ta-Nb-Hf-Zr-Ti),is systematically studied to examine changes in superconducting critical properties,critical temperature(T_(c)),critic...The high-entropy alloy(HEA)superconductor,Ta_(1/6)Nb_(2/6)Hf_(1/6)Zr_(1/6)Ti_(1/6)(Ta-Nb-Hf-Zr-Ti),is systematically studied to examine changes in superconducting critical properties,critical temperature(T_(c)),critical cur-rent density(J_(c)),and upper critical field(H_(c2)),concerning thermal treatment conditions.Annealing condi-tion affects Jc more significantly than T_(c)and H_(c2),with a large improvement of flux pinning force density(F_(p)).The Jc of bare sample is reduced to 10 A cm^(-2)at an applied magnetic field of approximately 1.5 T,whereas the sample annealed at 550℃for 12 h exhibits J_(c)>100 kA cm^(-2)up to around 4 T.Furthermore,the Vickers hardness(HVIT)of the Ta-Nb-Hf-Zr-Ti HEA superconductor notably increases from∼384 to 528 HVIT following a 24-h annealing at 500℃.These results demonstrate that thermal annealing is a powerful process to optimize both the superconducting and mechanical properties of high-entropy alloy superconductors.展开更多
Proximity effects between superconductors and ferromagnets(SC/FM)hold paramount importance in comprehending the spin competition transpiring at their interfaces.This competition arises from the interplay between Coope...Proximity effects between superconductors and ferromagnets(SC/FM)hold paramount importance in comprehending the spin competition transpiring at their interfaces.This competition arises from the interplay between Cooper pairs and ferromagnetic exchange interactions.The proximity effects between transition metal nitrides(TMNs)are scarcely investigated due to the formidable challenges of fabricating high-quality SC/FM interfaces.We fabricated heterostructures comprising SC titanium nitride(TiN)and FM iron nitride(Fe_(3)N)with precise chemical compositions and atomically well-defined interfaces.The magnetoresistance of Fe_(3)N/TiN heterostructures shows a distinct magnetic anisotropy and strongly depends on the external perturbations.Moreover,the superconducting transition temperatureT_(C) and critical field of TiN experience notable suppression when proximity to Fe_(3)N.We observe the intriguing competition of interfacial spin orientations near𝑇T_(C)(∼1.25 K).These findings not only add a new materials system for investigating the interplay between superconductor and ferromagnets,but also potentially provide a building block for future research endeavors and applications in the realms of superconducting spintronic devices.展开更多
Hydrogen-based compounds have attracted significant attention in recent years due to the discovery of conventional superconductivity with high critical temperature under high pressure,rekindling hopes for finding room...Hydrogen-based compounds have attracted significant attention in recent years due to the discovery of conventional superconductivity with high critical temperature under high pressure,rekindling hopes for finding roomtemperature superconductors.In this study,we investigated the vibrational and superconducting properties of H_(3)Sein the Im￣3m phase under pressures of 50-200GPa.Our approach combines the stochastic self-consistent harmonic approximation and first-principles calculations to account for the quantum and anharmonic effects of ions.According to the results,these effects significantly modify the crystal structure,increasing the inner pressure by approximately 8GPa compared to situations in which they are ignored.The phonon spectra suggest that when these effects are considered,the crystal stabilizes at pressures as low as approximately 61GPa,which is significantly lower than the previously predicted value of over 100GPa.Our calculations also highlight the critical role of quantum and anharmonic effects on the electron-phonon coupling properties.Neglecting these factors can result in a significant overestimation of the superconducting critical temperature(T_(c))by approximately 4K(200GPa)to 25K(125GPa).With anharmonic phonons,the T_(c) calculated from the Migdal-Eliashberg equations reaches 200K(μ⋆=0.1,λ=4.1)as the pressure decreases to 64GPa,indicating that the crystal is a rare high-Tc superconductor at moderate pressures.展开更多
We design two new layered indium halide compounds LaOInF_(2)and LaOInCl_(2)by means of first-principles calculations and evolutionary crystal structure prediction.We find both compounds crystallize in a tetragonal str...We design two new layered indium halide compounds LaOInF_(2)and LaOInCl_(2)by means of first-principles calculations and evolutionary crystal structure prediction.We find both compounds crystallize in a tetragonal structure with P4/nmm space group and have indirect band gaps of 2.58 eV and 3.21 eV,respectively.By substituting O with F,both of them become metallic and superconducting at low temperature.The F-doping leads to strong electron-phonon coupling in the low-energy acoustic phonon modes which is mainly responsible for the induced superconductivity.The total electron-phonon coupling strength are 1.86 and 1.48,while the superconducting transition temperature(T_(c))are about 7.2 K and 6.5 K with 10%and 5%F doping for LaOInF_(2)and LaOInCl_(2),respectively.展开更多
Since the discovery of hydride superconductors,a significant challenge has been to reduce the pressure required for their stabilization.In this context,we propose that alloying could be an effective strategy to achiev...Since the discovery of hydride superconductors,a significant challenge has been to reduce the pressure required for their stabilization.In this context,we propose that alloying could be an effective strategy to achieve this.We focus on a series of alloyed hydrides with the AMH_(6)composition,which can be made via alloying A15 AH_(3)(A=Al or Ga)with M(M=a group IIIB or IVB metal),and study their behavior under pressure.Seven of them are predicted to maintain the A15-type structure,similar to AH_(3)under pressure,providing a platform for studying the effects of alloying on the stability and superconductivity of AH_(3).Among these,the A15-type phases of AlZrH_(6)and AlHfH_(6)are found to be thermodynamically stable in the pressure ranges of 40–150 and 30–181 GPa,respectively.Furthermore,they remain dynamically stable at even lower pressures,as low as 13 GPa for AlZrH_(6)and 6 GPa for AlHfH_(6).These pressures are significantly lower than that required for stabilizing A15 AlH3.Additionally,the introduction of Zr or Hf increases the electronic density of states at the Fermi level compared with AlH3.This enhancement leads to higher critical temperatures(Tc)of 75 and 76 K for AlZrH_(6)and AlHfH_(6)at 20 and 10 GPa,respectively.In the case of GaMH_(6)alloys,where M represents Sc,Ti,Zr,or Hf,these metals reinforce the stability of the A15-type structure and reduce the lowest thermodynamically stable pressure for GaH_(3) from 160 GPa to 116,95,80,and 85 GPa,respectively.Particularly noteworthy are the A15-type GaMH_(6)alloys,which remain dynamically stable at low pressures of 97,28,5,and 6 GPa,simultaneously exhibiting high Tc of 88,39,70,and 49 K at 100,35,10,and 10 GPa,respectively.Overall,these findings enrich the family of A15-type superconductors and provide insights for the future exploration of high-temperature hydride superconductors that can be stabilized at lower pressures.展开更多
We construct a three-dimensional topological superconductor Bogoliubov–de Gennes(BdG)Hamiltonian with the normal state being a three-dimensional topological insulator.By introducing inter-orbital spin-triplet pairing...We construct a three-dimensional topological superconductor Bogoliubov–de Gennes(BdG)Hamiltonian with the normal state being a three-dimensional topological insulator.By introducing inter-orbital spin-triplet pairings term△3,there are topological Majorana nodes in the bulk and they are connected by Majorana Fermi arcs on the surface,similar to the case of Weyl semimetal.Furthermore,by adding an inversion-breaking term to the normal state,momentum-independent pairing terms with different parities can coexist in the Bd G Hamiltonian,which creates more Majorana modes similar to Andreev bound states and a richer phase diagram.展开更多
We construct a doped holographic superconductor in the Gubser–Rocha model,and realize a superconducting dome in the middle of the temperature-doping phase diagram.It is worth noting that unlike in previous research,t...We construct a doped holographic superconductor in the Gubser–Rocha model,and realize a superconducting dome in the middle of the temperature-doping phase diagram.It is worth noting that unlike in previous research,the profile of our dome shrinks inward near to zero temperature.From the numerical observation for the coupling dependence of the phase diagram,we find that the coupling between the two gauge fields plays a crucial role in the formation of the dome.We also analytically calculate the DC conductivity of the normal phase of the system in the momentum dissipation and obtain resistivity which is proportional to the temperature.The AC conductivity is calculated numerically.展开更多
In the 8 March 2023 issue of the journal Nature,a paper attracted global attention with the report of a new superconductor material exhibiting ground-breaking properties[1,2].A group led by Ranga P.Dias,assistant prof...In the 8 March 2023 issue of the journal Nature,a paper attracted global attention with the report of a new superconductor material exhibiting ground-breaking properties[1,2].A group led by Ranga P.Dias,assistant professor of mechanical engineering at the University of Rochester(Rochester,NY,USA),described a hydride material that superconducted at around room temperature,albeit at pressures 10000 times greater than atmospheric pressure[3].展开更多
The kagome superconductor CsV_(3)Sb_(5) has attracted widespread attention due to its rich correlated electron states including superconductivity, charge density wave(CDW), nematicity, and pair density wave. Notably, ...The kagome superconductor CsV_(3)Sb_(5) has attracted widespread attention due to its rich correlated electron states including superconductivity, charge density wave(CDW), nematicity, and pair density wave. Notably, the modulation of the intertwined electronic orders by the chemical doping is significant to illuminate the cooperation/competition between multiple phases in kagome superconductors. In this study, we have synthesized a series of tantalum-substituted Cs(V_(1-x)Ta_(x))_(3)Sb_(5) by a modified self-flux method. Electrical transport measurements reveal that CDW is suppressed gradually and becomes undetectable as the doping content of x is over 0.07. Concurrently, the superconductivity is enhanced monotonically from T_(c) ~ 2.8 K at x = 0 to 5.2 K at x = 0.12. Intriguingly, in the absence of CDW, Cs(V_(1-x)Ta_(x))_(3)Sb_(5)(x = 0.12) crystals exhibit a pronounced two-fold symmetry of the in-plane angular-dependent magnetoresistance(AMR) in the superconducting state, indicating the anisotropic superconducting properties in the Cs(V_(1-x)Ta_(x))_(3)Sb_(5). Our findings demonstrate that Cs(V_(1-x)Ta_(x))_(3)Sb_(5) with the non-trivial band topology is an excellent platform to explore the superconductivity mechanism and intertwined electronic orders in quantum materials.展开更多
We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion ...We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion symmetry. We investigate how the shot noise properties vary as the relative amplitude between the two parity components in the pairing potential is changed. It is demonstrated that some characteristics of the electrical shot noise properties of such tunnel junctions may depend sensitively on the relative amplitude between the two parity components in the pairing potential, and some significant changes may occur in the electrical shot noise properties when the relative amplitude between the two parity components is varied from the singlet s-wave pairing dominated regime to the chiral triplet p-wave pairing dominated regime. In the chiral triplet p-wave pairing dominated regime, the ratio of noise power to electric current is close to 2e both in the in-gap and in the out-gap region. In the singlet s-wave pairing dominated regime, the value of this ratio is close to 4e in the inner gap region but may reduce to about 2e in the outer gap region as the relative amplitude of the chiral triplet pairing component is increased. The variations of the differential shot noise with the bias voltage also exhibit some significantly different features in different regimes. Such different features can serve as useful diagnostic tools for the determination of the relative magnitude of the two parity components in the pairing potential.展开更多
Composition/structure-dependent superconductivity for FeSe-based superconductors attracted great attention not only due to their high superconducting transition temperatures(TC),but also for understanding the origin o...Composition/structure-dependent superconductivity for FeSe-based superconductors attracted great attention not only due to their high superconducting transition temperatures(TC),but also for understanding the origin of iron-based superconductivity.Here,we report a new Fe-poor organic-inorganic hybrid material Fe_(14)Se_(16)(tepa)0.8 with a paramagnetic-diamagnetic transition at∼42 K grown by a high-temperature organic-solution-phase method with soluble iron/selenium sources in a tepa solution,alternative to previous intercalation strategies.The Fe_(14)Se_(16)(tepa)0.8 phase is in a tetragonal layered hybrid structure with a nanoplate shape.Composition analyses reveal a Fe-poor characteristic of the hybrid in contrast to previous FeSe-intercalated superconductor,and selected area electron diffraction pattern is featured by Fe_(3)Se_(4) superstructures with a√2×√2 of Fe vacancy order.Ab initio density functional calculations show that minus Fe_(3)Se_(4) ions are stable in the hybrid and∼0.25e-/Fe_(0.75)Se is obviously larger than the reported values of approximately 0.2e-/FeSe in other FeSe-intercalated superconductors.Typical hysteresis loops and temperature dependence of dc/ac susceptibilities of the Fe_(14)Se_(16)(tepa)0.8 measured below∼42 K suggest a presence of the Meissner effect in this material.Effects of synthesis conditions on structures and magnetic properties of the hybrids show a magnetic evolution from a long-range ferrimagnetic(FIM)order of Fe_(14)Se_(16)(tepa)to a coexistence of FIM and superconducting(SC)orders of Fe_(14)Se_(16)(tepa)0.9 and an SC order of Fe_(14)Se_(16)(tepa)0.8.X-ray absorption spectrum(XAS)confirms the presence of ferric/ferrous irons.Mössbauer studies reveal that the high-TC superconductivity originates from a suppression of the FIM order through tuning the spin states of irons from high-spin Fe^(3+)(S=5/2)and Fe^(2+)(S=2)in the Fe_(14)Se_(16)(tepa)to low-spin Fe^(3+)(S=1/2)and Fe^(2+)(S=0)in the Fe_(14)Se_(16)(tepa)0.8.Although no zero resistance is detected even at a temperature of 2 K,the resistivity at 2 K decreases by more than 1600 times compared to that in a normal state calculated by a variable range hopping(VRH)model,suggesting that the high-TC superconductivity of Fe_(14)Se_(16)(tepa)0.8 is possible.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.92365302,92065201,12488101,22325203,92265105,12074247,12174252,and 52102336)the Ministry of Science and Technology of China(Grant Nos.2019YFA0308600 and 2020YFA0309000)+1 种基金the Science and Technology Commission of Shanghai Municipality(Grant Nos.2019SHZDZX01,19JC1412701,20QA1405100,24LZ1401000,and LZPY2024-04)the financial support from Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302500)。
文摘Topological superconductor islands are thought to be the building blocks of topological quantum bits.We produced single-crystalline VSi_(x)islands with well-defined side facets and island size more than 200nm using molecular beam epitaxy on Si substrate heated to 950℃throughout the growth process.By means of scanning tunneling spectroscopy,we revealed dynamical Coulomb blockade and superconductivity on isolated islands and on islands being connected by superconducting wetting layer respectively.Bi_(2)Te_(3)films were further deposited on VSi_(x)islands.Robust and homogenous proximity effect induced superconductivity was observed on various facets of the Bi_(2)Te_(3)/VSi_(x)hetero-nanostructure.Furthermore,our high-resolution spectroscopy identified Bosonic mode excitations on the topological superconductor islands.These results may establish a playground for the vortex Majorana islands.
基金supported by the National Key Research and Development Program of China(Grant Nos.2024YFA1611103 and 2022YFA1403203)the Innovation Program for Quantum Science and Technology(Grant Nos.2024ZD0301300 and 2021ZD0302802)the National Natural Science Foundation of China(Grant Nos.12474128,12374133,12204008,and 12104004)。
文摘Iron-based superconductors(FeSCs)feature a complex phase diagram,and their diverse cleavage terminations offer a versatile platform for modulating surface electronic states and investigating the underlying superconducting mechanisms.In this study,we explore the surface modulation of KCa_(2)Fe_(4)As_(4)F_(2)using scanning tunneling microscopy/spectroscopy.Cryogenically cleaved surfaces reveal multiple configurations,including√2×√2 reconstruction,1×2 and 1×3 stripes,as well as nanoscale vacancies.Reducing potassium coverage induces hole doping,which shifts the density of states peak toward the Fermi level and suppresses the superconducting gap from 4.8 meV to 3.2 meV.This behavior is reminiscent of the Van Hove singularity observed in hole-doped 122-type FeSCs.The band structure does not undergo a simple rigid shift,and the evolution of superconductivity can be attributed to the interplay between surface carriers and electronic correlations.Additionally,a V-shaped gap is observed at a unique location preserving the FeAs bilayer structure,where interlayer coupling effects are likely involved.The diversity of surface structures and electronic states in K12442 enhances our understanding of FeSCs and facilitates the modulation and application of FeAs superconducting layers.
基金supported by the National Natural Science Foundation of China(Nos.12374004 and 12174141)the National Key R&D Program of China(No.2023YFA1406200)。
文摘Exploring novel superconductors is a crucial topic in condensed matter physics.There are few reports on the superconductivity of fluorine due to the extremely high pressures required for its metallization.Here,metallization and superconductivity of fluorine were achieved in MgF_(5)at 120 GPa by exploiting the high-pressure s-d transition of doped Mg.The unexpected Mg-F covalent bonding induced by Mg-d and F-p orbital interactions led to fluorine metallization and the formation of an F skeleton similar to a H-cage.The high density of states(DOS)from the F skeleton and phonon softening from strong Fermi surface nesting contribute to a high superconducting transition temperature(Tc).The Tc of Pmmm-MgF_(5)at 120 GPa is 14.02 K,with strong electron-phonon coupling(λ=0.84),which is close to that of Li_(6)P at 270 GPa(λ=1.01).This is the first observation of superconductivity in main-group metal fluorides.Additionally,two near-monatomic F atoms exist in the interstitial region of MgF_(5),significantly enhancing electron-phonon coupling.This work challenges the traditional view of main-group metal fluorides and provides deeper insights into the superconductivity and physicochemical properties of fluorine.
基金supported by the National Natural Science Foundation of China(Grant Nos.12232005 and 12072101).
文摘Large-grain REBa_(2)Cu_(3)O_(7-δ)(REBCO,RE=rare earth)bulk superconductors offer promising magnetic field trapping capabilities due to their high critical current density,making them ideal for many important applications such as trapped field magnets.However,for such large-grain superconductor bulks,there are lots of voids and cracks forming during the process of melting preparation,and some of them can be up to hundreds of microns or even millimeters in size.Consequently,these larger size voids/cracks pose a great threat to the strength of the bulks due to the inherent brittleness of superconductor REBCO materials.In order to ensure the operational safety of related superconducting devices with bulk superconductors,it is firstly important to accurately detect these voids/cracks in them.In this paper,we proposed a method for quantitatively evaluating multiple voids/cracks in bulk superconductors through the magnetic field and displacement response signals at superconductor bulk surface.The proposed method utilizes a damage index constructed from the magnetic field signals and displacement responses to identify the number and preliminary location of multiple defects.By dividing the detection area into subdomains and combining the magnetic field signals with displacement responses within each subdomain,a particle swarm algorithm was employed to evaluate the location and size parameters of the defects.In contrast to other evaluation methods using only magnetic field or displacement response signals,the combined evaluation method using both signals can identify the number of cracks effectively.Numerical studies demonstrate that the morphology of voids and cracks reconstructed using the proposed algorithm ideally matches real defects and is applicable to cases where voids and cracks coexist.This study provides a theoretical basis for the quantitative detection of voids/cracks in bulk superconductors.
基金supported by the National Key Research and Development Program of China(Grant Nos.2024YFA1408400,2023YFA1406100,2023YFA1607400,2022YFA1403800,and 2022YFA1403203)the National Natural Science Foundation of China(Grant Nos.12474055,12404067,12025408,52025026,and U23A6003)+3 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB33000000)the Chinese Academy of Sciences President’s International Fellowship Initiative(Grant No.2024PG0003)the Outstanding Member of Youth Promotion Association of Chinese Academy of Sciences(Grant No.Y2022004)supported by the CAC station of Synergetic Extreme Condition User Facility(SECUF,https://cstr.cn/31123.02.SECUF)。
文摘Compared to traditional superhard materials with high electron density and short,strong covalent bonds,alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness.Breaking through the limits of alloy materials is a preface and long-term topic,which is of great significance and value for improving the comprehensive mechanical properties of alloy materials.Here,we report on the discovery of a cubic alloy semiconducting material Ti_(2)Co with a large Vickers of hardness K_(v)^(exp)∼6.7GPa and low fracture toughness of K_(IC)^(exp)∼1.51MPa·m^(1/2).Unexpectedly,the K_(v)^(exp)∼6.7GPa is nearly triple of the K_(v)^(cal)∼2.66GPa predicted by density functional theory(DFT)calculations and theK_(IC)^(exp)∼1.51MPa·m^(1/2)is about one or two orders of magnitude smaller than that of ordinary titanium alloy materials(K_(IC)^(exp)∼30-120MPa·m^(1/2)).These specifications place Ti_(2)Co far from the phase space of the known alloy materials.Upon incorporation of oxygen into structural void positions,both values were simultaneously improved for Ti_(4)Co_(2)O to∼9.7GPa and∼2.19MPa·m^(1/2),respectively.Further DFT calculations on the electron localization function of Ti_(4)Co_(2)X(X=B,C,N,O)vs.the interstitial elements indicate that these simultaneous improvements originate from the coexistence of Ti-Co metallic bonds,the emergence of newly oriented Ti-X covalent bonds,and the increase of electron concentration.Moreover,the large difference between K_(v)^(exp)and K_(v)^(cal)of Ti_(2)Co suggests underlying mechanism concerning the absence of the O(16d)or Ti_(2)-O bonds in the O-(Ti_(2))_(6) octahedron.This discovery proposes a new pathway to simultaneously improve the comprehensive mechanical performances and illuminates the path of exploring superconducting materials with excellent mechanical performances.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.62476278,12434009,and 12204533)the National Key R&D Program of China(Grant No.2024YFA1408601)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302402)。
文摘The discovery of new superconducting materials,particularly those exhibiting high critical temperature(Tc),has been a vibrant area of study within the field of condensed matter physics.Conventional approaches primarily rely on physical intuition to search for potential superconductors within the existing databases.However,the known materials only scratch the surface of the extensive array of possibilities within the realm of materials.
基金Project supported by the National Key Research and Development Project of China(Grant Nos.2024YFA1207700 and 2022YFA1204100)the National Natural Science Foundation of China(Grant No.62488201)+2 种基金the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-003)the Youth Innovation Promotion Association(Grant No.2023005)the Innovation Program of Quantum Science and Technology(Grant No.2021ZD0302700)。
文摘The interplay between 2a_(0)×2a_(0)charge density wave(CDW),nematicity and superconductivity in AV_(3)Sb_(5)(A=K,Rb,Cs)compounds gives rise to a rich landscape of intriguing physical phenomena.In addition to the 2a_(0)×2a_(0)CDW,a unidirectional 4a_(0)stripe CDW is also observed on the Sb surface of RbV3Sb5and CsV3Sb5.However,reports of stripe-like CDWs in KV3Sb5have been limited.Here,we report the first observation of a long-range unidirectional stripe order with a 6a_(0)modulation period on the Sb surface of KV_(3)Sb_(5),coexisting with the 2a_(0)×2a_(0)CDW.Notably,the intensity of the6a_(0)stripes in STM topographies exhibits pronounced contrast reversal between opposite bias voltages.Additionally,the wave vector of the 6a_(0)modulation shows no energy-dependent dispersion,confirming its CDW origin.Furthermore,the6a_(0)CDW is robust under a 7 T out-of-plane magnetic field and persists over a temperature range from 215 mK to 720 mK.These results provide compelling evidence for the emergence of a long-range unidirectional CDW in KV_(3)Sb_(5).
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1403903,2023YFA1406100,2018YFA0305800,and 2022YFA1204100)the National Natural Science Foundation of China(Grant Nos.12304075,11834014,61888102,and 12447101)+2 种基金Chinese Academy of Sciences(Grant Nos.XDB33010200 and 2022YSBR-048)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB28000000)the National Science and Technology Major Project(Grant No.2024ZD0300500)。
文摘The kagome lattice,naturally encompassing Dirac fermions,flat bands,and van Hove singularities,tends to intertwine exotic electronic states.Revealing the characteristics of its Fermi surface will help clarify the nature of the complex quantum phenomena in kagome material.Here we report the Fermi surface properties of the novel kagome metal CsTi_(3)Bi_(5)by the de Haas-van Alphen oscillations.The observed oscillations are clear and consist of six principal frequencies ranging from 214 T to 1013 T.The angular dependence of the frequency implies a quasi-two-dimensional electronic structure.In addition,the geometry phase corresponding to 281 T,determined by direct Lifshitz-Kosevich formula fitting,yields a value close toπ,which may indicate a band structure with nontrivial topological property.These results underscore the potential of CsTi_(3)Bi_(5)as a promising platform to explore the interplay between topological order,electronic nematicity,and superconductivity.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MIST)(Nos.2021R1A2C2010925,RS-2023-00240326,and RS-2023-00220471)Basic Science Research Program through the NRF of Korea funded by the Ministry of Education(Nos.NRF-2019R1F1A1055284 and NRF-2021R1I1A1A01043885).
文摘The high-entropy alloy(HEA)superconductor,Ta_(1/6)Nb_(2/6)Hf_(1/6)Zr_(1/6)Ti_(1/6)(Ta-Nb-Hf-Zr-Ti),is systematically studied to examine changes in superconducting critical properties,critical temperature(T_(c)),critical cur-rent density(J_(c)),and upper critical field(H_(c2)),concerning thermal treatment conditions.Annealing condi-tion affects Jc more significantly than T_(c)and H_(c2),with a large improvement of flux pinning force density(F_(p)).The Jc of bare sample is reduced to 10 A cm^(-2)at an applied magnetic field of approximately 1.5 T,whereas the sample annealed at 550℃for 12 h exhibits J_(c)>100 kA cm^(-2)up to around 4 T.Furthermore,the Vickers hardness(HVIT)of the Ta-Nb-Hf-Zr-Ti HEA superconductor notably increases from∼384 to 528 HVIT following a 24-h annealing at 500℃.These results demonstrate that thermal annealing is a powerful process to optimize both the superconducting and mechanical properties of high-entropy alloy superconductors.
基金supported by the National Key Research and Development Program of China(Grant Nos.2020YFA0309100 and 2019YFA0308500)the National Natural Science Foundation of China(Grant Nos.U22A20263,52250308,and 11974390)+3 种基金the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-084)(E.J.G.)Special Research Assistant(Q.J.),the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB33030200)(K.J.)the China Postdoctoral Science Foundation(Grant No.2022M723353)the Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scattering Science and Technology(Grant No.HTCSNS-DG-CD-0080/2021).
文摘Proximity effects between superconductors and ferromagnets(SC/FM)hold paramount importance in comprehending the spin competition transpiring at their interfaces.This competition arises from the interplay between Cooper pairs and ferromagnetic exchange interactions.The proximity effects between transition metal nitrides(TMNs)are scarcely investigated due to the formidable challenges of fabricating high-quality SC/FM interfaces.We fabricated heterostructures comprising SC titanium nitride(TiN)and FM iron nitride(Fe_(3)N)with precise chemical compositions and atomically well-defined interfaces.The magnetoresistance of Fe_(3)N/TiN heterostructures shows a distinct magnetic anisotropy and strongly depends on the external perturbations.Moreover,the superconducting transition temperatureT_(C) and critical field of TiN experience notable suppression when proximity to Fe_(3)N.We observe the intriguing competition of interfacial spin orientations near𝑇T_(C)(∼1.25 K).These findings not only add a new materials system for investigating the interplay between superconductor and ferromagnets,but also potentially provide a building block for future research endeavors and applications in the realms of superconducting spintronic devices.
基金Natural Science Foundation Project(Grant No.20230101280JC)of Jilin Provincial Department of Science and Technology.
文摘Hydrogen-based compounds have attracted significant attention in recent years due to the discovery of conventional superconductivity with high critical temperature under high pressure,rekindling hopes for finding roomtemperature superconductors.In this study,we investigated the vibrational and superconducting properties of H_(3)Sein the Im￣3m phase under pressures of 50-200GPa.Our approach combines the stochastic self-consistent harmonic approximation and first-principles calculations to account for the quantum and anharmonic effects of ions.According to the results,these effects significantly modify the crystal structure,increasing the inner pressure by approximately 8GPa compared to situations in which they are ignored.The phonon spectra suggest that when these effects are considered,the crystal stabilizes at pressures as low as approximately 61GPa,which is significantly lower than the previously predicted value of over 100GPa.Our calculations also highlight the critical role of quantum and anharmonic effects on the electron-phonon coupling properties.Neglecting these factors can result in a significant overestimation of the superconducting critical temperature(T_(c))by approximately 4K(200GPa)to 25K(125GPa).With anharmonic phonons,the T_(c) calculated from the Migdal-Eliashberg equations reaches 200K(μ⋆=0.1,λ=4.1)as the pressure decreases to 64GPa,indicating that the crystal is a rare high-Tc superconductor at moderate pressures.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.2243300003)the National Natural Science Foundation of China(Grant No.12074041)the Fundamental Research Program of Shanxi Province,China(Grant No.202203021222228).The calculations were carried out with high performance computing cluster of Beijing Normal University in Zhuhai.
文摘We design two new layered indium halide compounds LaOInF_(2)and LaOInCl_(2)by means of first-principles calculations and evolutionary crystal structure prediction.We find both compounds crystallize in a tetragonal structure with P4/nmm space group and have indirect band gaps of 2.58 eV and 3.21 eV,respectively.By substituting O with F,both of them become metallic and superconducting at low temperature.The F-doping leads to strong electron-phonon coupling in the low-energy acoustic phonon modes which is mainly responsible for the induced superconductivity.The total electron-phonon coupling strength are 1.86 and 1.48,while the superconducting transition temperature(T_(c))are about 7.2 K and 6.5 K with 10%and 5%F doping for LaOInF_(2)and LaOInCl_(2),respectively.
基金supported by the Natural Science Foundation of China(Grant Nos.52022089,52372261,52288102,and 11964026)the National Key R&D Program of China(Grant No.2022YFA1402300)+5 种基金the Natural Science Foundation of Hebei Province(Grant No.E2022203109)the Doctoral Fund of Henan University of Technology(Grant No.31401579)P.L.thanks the Science and Technology Leading Talents and Innovation Team Building Projects of the Inner Mongolia Autonomous Region(Grant No.GXKY22060)financial support from the Spanish Ministry of Science and Innovation(Grant No.FIS2019-105488GB-I00)the Department of Education,Universities and Research of the Basque Government and the University of the Basque Country(Grant No.IT1707-22)the National Science Foundation(Grant No.DMR-2136038)for financial support.
文摘Since the discovery of hydride superconductors,a significant challenge has been to reduce the pressure required for their stabilization.In this context,we propose that alloying could be an effective strategy to achieve this.We focus on a series of alloyed hydrides with the AMH_(6)composition,which can be made via alloying A15 AH_(3)(A=Al or Ga)with M(M=a group IIIB or IVB metal),and study their behavior under pressure.Seven of them are predicted to maintain the A15-type structure,similar to AH_(3)under pressure,providing a platform for studying the effects of alloying on the stability and superconductivity of AH_(3).Among these,the A15-type phases of AlZrH_(6)and AlHfH_(6)are found to be thermodynamically stable in the pressure ranges of 40–150 and 30–181 GPa,respectively.Furthermore,they remain dynamically stable at even lower pressures,as low as 13 GPa for AlZrH_(6)and 6 GPa for AlHfH_(6).These pressures are significantly lower than that required for stabilizing A15 AlH3.Additionally,the introduction of Zr or Hf increases the electronic density of states at the Fermi level compared with AlH3.This enhancement leads to higher critical temperatures(Tc)of 75 and 76 K for AlZrH_(6)and AlHfH_(6)at 20 and 10 GPa,respectively.In the case of GaMH_(6)alloys,where M represents Sc,Ti,Zr,or Hf,these metals reinforce the stability of the A15-type structure and reduce the lowest thermodynamically stable pressure for GaH_(3) from 160 GPa to 116,95,80,and 85 GPa,respectively.Particularly noteworthy are the A15-type GaMH_(6)alloys,which remain dynamically stable at low pressures of 97,28,5,and 6 GPa,simultaneously exhibiting high Tc of 88,39,70,and 49 K at 100,35,10,and 10 GPa,respectively.Overall,these findings enrich the family of A15-type superconductors and provide insights for the future exploration of high-temperature hydride superconductors that can be stabilized at lower pressures.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12174067 and 11804223)。
文摘We construct a three-dimensional topological superconductor Bogoliubov–de Gennes(BdG)Hamiltonian with the normal state being a three-dimensional topological insulator.By introducing inter-orbital spin-triplet pairings term△3,there are topological Majorana nodes in the bulk and they are connected by Majorana Fermi arcs on the surface,similar to the case of Weyl semimetal.Furthermore,by adding an inversion-breaking term to the normal state,momentum-independent pairing terms with different parities can coexist in the Bd G Hamiltonian,which creates more Majorana modes similar to Andreev bound states and a richer phase diagram.
基金supported by the National Natural Science Foundation of China(Grant Nos.12275166,11875184,12147158 and 11805117)the NFSC-NFR joint program 12311540141.
文摘We construct a doped holographic superconductor in the Gubser–Rocha model,and realize a superconducting dome in the middle of the temperature-doping phase diagram.It is worth noting that unlike in previous research,the profile of our dome shrinks inward near to zero temperature.From the numerical observation for the coupling dependence of the phase diagram,we find that the coupling between the two gauge fields plays a crucial role in the formation of the dome.We also analytically calculate the DC conductivity of the normal phase of the system in the momentum dissipation and obtain resistivity which is proportional to the temperature.The AC conductivity is calculated numerically.
文摘In the 8 March 2023 issue of the journal Nature,a paper attracted global attention with the report of a new superconductor material exhibiting ground-breaking properties[1,2].A group led by Ranga P.Dias,assistant professor of mechanical engineering at the University of Rochester(Rochester,NY,USA),described a hydride material that superconducted at around room temperature,albeit at pressures 10000 times greater than atmospheric pressure[3].
基金Project supported by the National Key R&D Program of China(Grant No.2022YFA1204100)the National Natural Science Foundation of China(Grant No.62488201)+1 种基金the Chinese Academy of Sciences(Grant Nos.XDB33030000,ZDBS-SSW-WHC001,YSBR-003,and YSBR-053)Innovation Program of Quantum Science and Technology(Grant No.2021ZD0302700)。
文摘The kagome superconductor CsV_(3)Sb_(5) has attracted widespread attention due to its rich correlated electron states including superconductivity, charge density wave(CDW), nematicity, and pair density wave. Notably, the modulation of the intertwined electronic orders by the chemical doping is significant to illuminate the cooperation/competition between multiple phases in kagome superconductors. In this study, we have synthesized a series of tantalum-substituted Cs(V_(1-x)Ta_(x))_(3)Sb_(5) by a modified self-flux method. Electrical transport measurements reveal that CDW is suppressed gradually and becomes undetectable as the doping content of x is over 0.07. Concurrently, the superconductivity is enhanced monotonically from T_(c) ~ 2.8 K at x = 0 to 5.2 K at x = 0.12. Intriguingly, in the absence of CDW, Cs(V_(1-x)Ta_(x))_(3)Sb_(5)(x = 0.12) crystals exhibit a pronounced two-fold symmetry of the in-plane angular-dependent magnetoresistance(AMR) in the superconducting state, indicating the anisotropic superconducting properties in the Cs(V_(1-x)Ta_(x))_(3)Sb_(5). Our findings demonstrate that Cs(V_(1-x)Ta_(x))_(3)Sb_(5) with the non-trivial band topology is an excellent platform to explore the superconductivity mechanism and intertwined electronic orders in quantum materials.
文摘We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion symmetry. We investigate how the shot noise properties vary as the relative amplitude between the two parity components in the pairing potential is changed. It is demonstrated that some characteristics of the electrical shot noise properties of such tunnel junctions may depend sensitively on the relative amplitude between the two parity components in the pairing potential, and some significant changes may occur in the electrical shot noise properties when the relative amplitude between the two parity components is varied from the singlet s-wave pairing dominated regime to the chiral triplet p-wave pairing dominated regime. In the chiral triplet p-wave pairing dominated regime, the ratio of noise power to electric current is close to 2e both in the in-gap and in the out-gap region. In the singlet s-wave pairing dominated regime, the value of this ratio is close to 4e in the inner gap region but may reduce to about 2e in the outer gap region as the relative amplitude of the chiral triplet pairing component is increased. The variations of the differential shot noise with the bias voltage also exhibit some significantly different features in different regimes. Such different features can serve as useful diagnostic tools for the determination of the relative magnitude of the two parity components in the pairing potential.
基金supported by the National Natural Science Foundation of China(Nos.52371203,51971221 and 52031014).
文摘Composition/structure-dependent superconductivity for FeSe-based superconductors attracted great attention not only due to their high superconducting transition temperatures(TC),but also for understanding the origin of iron-based superconductivity.Here,we report a new Fe-poor organic-inorganic hybrid material Fe_(14)Se_(16)(tepa)0.8 with a paramagnetic-diamagnetic transition at∼42 K grown by a high-temperature organic-solution-phase method with soluble iron/selenium sources in a tepa solution,alternative to previous intercalation strategies.The Fe_(14)Se_(16)(tepa)0.8 phase is in a tetragonal layered hybrid structure with a nanoplate shape.Composition analyses reveal a Fe-poor characteristic of the hybrid in contrast to previous FeSe-intercalated superconductor,and selected area electron diffraction pattern is featured by Fe_(3)Se_(4) superstructures with a√2×√2 of Fe vacancy order.Ab initio density functional calculations show that minus Fe_(3)Se_(4) ions are stable in the hybrid and∼0.25e-/Fe_(0.75)Se is obviously larger than the reported values of approximately 0.2e-/FeSe in other FeSe-intercalated superconductors.Typical hysteresis loops and temperature dependence of dc/ac susceptibilities of the Fe_(14)Se_(16)(tepa)0.8 measured below∼42 K suggest a presence of the Meissner effect in this material.Effects of synthesis conditions on structures and magnetic properties of the hybrids show a magnetic evolution from a long-range ferrimagnetic(FIM)order of Fe_(14)Se_(16)(tepa)to a coexistence of FIM and superconducting(SC)orders of Fe_(14)Se_(16)(tepa)0.9 and an SC order of Fe_(14)Se_(16)(tepa)0.8.X-ray absorption spectrum(XAS)confirms the presence of ferric/ferrous irons.Mössbauer studies reveal that the high-TC superconductivity originates from a suppression of the FIM order through tuning the spin states of irons from high-spin Fe^(3+)(S=5/2)and Fe^(2+)(S=2)in the Fe_(14)Se_(16)(tepa)to low-spin Fe^(3+)(S=1/2)and Fe^(2+)(S=0)in the Fe_(14)Se_(16)(tepa)0.8.Although no zero resistance is detected even at a temperature of 2 K,the resistivity at 2 K decreases by more than 1600 times compared to that in a normal state calculated by a variable range hopping(VRH)model,suggesting that the high-TC superconductivity of Fe_(14)Se_(16)(tepa)0.8 is possible.
