The stability of superconductivity in superconductors is widely recognized to be determined by various factors,including charge,spin,orbit,lattice,and other related degrees of freedom.Here,we report our findings on th...The stability of superconductivity in superconductors is widely recognized to be determined by various factors,including charge,spin,orbit,lattice,and other related degrees of freedom.Here,we report our findings on the pressure-induced coevolution of superconductivity and Hall coefficient in KCa_(2)Fe_(4)As_(24F_(2),an iron-based superconductor possessing a hybrid crystal structure combining KFe_(2)As_(2) and CaFeAsF.Our investigation,involving high-pressure resistance,Hall effect and x-ray diffraction(XRD) measurements,allows us to observe the connection of the superconductivity and Hall coefficient with the anisotropic lattice shrinkage.We find that its ambient-pressure tetragonal(T) phase presents a collapse starting at around 18 GPa,where the sign of the Hall coefficient(R_(H)) changes from positive to negative.Upon further compression,both superconducting transition temperature(T_(c)) and R_(H) exhibit a monotonous decrease.At around 41 GPa,the superconductivity is completely suppressed(T_(c)=0),where the parameter a begins to decline again and the Hall coefficient remains nearly unchanged.Our experiment results clearly demonstrate that the pressure-induced anisotropic lattice collapse plays a crucial role in tuning the interplay among multiple degrees of freedom in the superconducting system and,correspondingly,the stability of the superconductivity.展开更多
We report on soft c-axis point-contact Andreev reflection(PCAR)spectroscopy combining with resistivity measurements on BaFe_(2)(As_(0.7)P_(0.3))_(2),to elucidate the superconducting gap structure in the vicinity of th...We report on soft c-axis point-contact Andreev reflection(PCAR)spectroscopy combining with resistivity measurements on BaFe_(2)(As_(0.7)P_(0.3))_(2),to elucidate the superconducting gap structure in the vicinity of the quantum critical point.A double peak at the gap edge plus a dip feature at zero-bias has been observed on the PCAR spectra,indicative of the presence of a nodeless gap in BaFe_(2)(As_(0.7)P_(0.3))_(2).Detailed analysis within a sophisticated theoretical model reveals an anisotropic gap with deep gap minima.The PCARs also feature additional structures related to the electron-bosonic coupling mode.Using the extracted superconducting energy gap value,a characteristic bosonic energy Ω_(b) and its temperature dependence are obtained,comparable with the spin-resonance energy observed in neutron scattering experiment.These results indicate a magnetism-driven quantum critical point in the BaFe_(2)(As_(1-x)P_(x))_(2) system.展开更多
We report a systematic investigation on c-axis point-contact Andreev reflection （PCAR） in BaFe2-xNixAs2 superconducting single crystals from underdoped to overdoped regions （0.075≤ x ≤0.15）. At low temperatures,...We report a systematic investigation on c-axis point-contact Andreev reflection （PCAR） in BaFe2-xNixAs2 superconducting single crystals from underdoped to overdoped regions （0.075≤ x ≤0.15）. At low temperatures, an in-gap sharp peak at low-bias voltage is observed in PCAR for overdoped samples, in contrast to the case of underdoped junctions, in which an in-gap plateau is observed. The variety of the conductance spectra with doping can be well described by using a generalized Blonder-Tinkham-Klapwijk formalism with an angle-dependent gap. This gap shows a clear crossover from a nodeless in the underdoped side to a nodal feature in the overdoped region. This result provides evidence of the doping-induced evolution of the superconducting order parameter when the inter-pocket and intra-pocket scattering are tuned through doping, as expected in the s± scenario.展开更多
We use femtosecond time-resolved optical reflectivity to study the photoexcited quasiparticle(QP)dynamics in the iron-based 112 type superconducting(SC)samples Ca0.82La0.18Fe1-xNixAs2,with x=0 and 0.024.In the parent ...We use femtosecond time-resolved optical reflectivity to study the photoexcited quasiparticle(QP)dynamics in the iron-based 112 type superconducting(SC)samples Ca0.82La0.18Fe1-xNixAs2,with x=0 and 0.024.In the parent sample,a fast and a slow relaxation emerge at temperatures below the magnetic-structure(MS)transition Tms≈50 K and the SC transition Tc≈33 K,respectively.The latter obviously corresponds to an SC QP dynamics,which is further confirmed in the x=0.024 sample with Tc≈25 K.The former suggests that a partial of photoexcited QP relaxation through a pesudogap(PG)channel,which is absent in the doped x=0.024 sample without the MS transition.展开更多
Complex permittivity and electrical impedance have been measured along the c-axis in single crystals BaFe_2 As_2,which are the conductors known as the parent compound of 122-type iron superconductor. The resultant rel...Complex permittivity and electrical impedance have been measured along the c-axis in single crystals BaFe_2 As_2,which are the conductors known as the parent compound of 122-type iron superconductor. The resultant relative errors defined in the study indicate the existence of the transformation between complex permittivity and electrical impedance in the conductors, and these two physics quantities possibly reveal different aspects of the consistent superconductivityrelevant physics picture.展开更多
High resolution angle-resolved photoemission spectroscopy(ARPES)measurements are carried out on CaKFe_4 As_4,KCa_2 Fe_4 As_4 F_2 and(Ba_(0.6)K_(0.4))Fe_2 As_2 superconductors.Clear evidence of band folding between the...High resolution angle-resolved photoemission spectroscopy(ARPES)measurements are carried out on CaKFe_4 As_4,KCa_2 Fe_4 As_4 F_2 and(Ba_(0.6)K_(0.4))Fe_2 As_2 superconductors.Clear evidence of band folding between the Brillouin zone center and corners with a(π,π)wave vector has been found from the measured Fermi surface and band structures in all the three kinds of superconductors.A dominant √2×√2 surface reconstruction is observed on the cleaved surface of CaKFe_4As_4 by scanning tunneling microscopy(STM)measurements.We propose that the commonly observed √2×√2 reconstruction in the FeAs-based superconductors provides a general scenario to understand the origin of the(π,π)band folding.Our observations provide new insights in understanding the electronic structure and superconductivity mechanism in iron-based superconductors.展开更多
Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain...Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr1 _xBaxFel.97Nio.03As2, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Srl xBaxFe2As2 is determined by the strength of the magnetic-elastic coupling.展开更多
We present magnetotransport studies on a series of BaFe2_xNixAs2 （0.03 〈 x 〈 0.10） single crystals. In the un- derdoped （x = 0.03） non-superconducting sample, the temperature-dependent resistivity exhibits a pea...We present magnetotransport studies on a series of BaFe2_xNixAs2 （0.03 〈 x 〈 0.10） single crystals. In the un- derdoped （x = 0.03） non-superconducting sample, the temperature-dependent resistivity exhibits a peak at 22 K, which is associated with the onset of filamentary superconductivity （FLSC）. FLSC is suppressed by an external magnetic field in a manner similar to the suppression of bulk superconductivity in an optimally-doped （x = 0.10） compound, suggesting the same possible origin as the bulk superconductivity. Our magnetoresistivity measurements reveal that FLSC persists up to the optimal doping and disappears in the overdoped regime where the long-range antiferromagnetic order is completely suppressed, pointing to a close relation between FLSC and the magnetic order.展开更多
We have studied the angular magnetoresistance of iron pnictides BaFe_（2-x）Ni_xAs_2, which shows clear 180 degree periodicity as fitted by a cosine function. In the x = 0.065 sample, the phase of the two-fold symmetr...We have studied the angular magnetoresistance of iron pnictides BaFe_（2-x）Ni_xAs_2, which shows clear 180 degree periodicity as fitted by a cosine function. In the x = 0.065 sample, the phase of the two-fold symmetry changes 90 degrees above the tetragonal-to-orthorhombic structural transition temperature Ts. Since the phase at low temperature is associated with the rotation of orthorhombic domains by magnetic field, we show that even vacuum grease can push the presence of orthorhombic domains at temperatures much higher than Ts. Our results suggest that residual stress may have significant effects in studying the nematic orders and its fluctuations in iron pnictides.展开更多
The iron-chalcogenide superconductor FeTe_(1-x)Se_(x) displays a variety of exotic features distinct from iron pnictides.Although much effort has been devoted to understanding the interplay between magnetism and super...The iron-chalcogenide superconductor FeTe_(1-x)Se_(x) displays a variety of exotic features distinct from iron pnictides.Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x=0.5,the existence of a spin glass phase with short-range magnetic order in the doping range(x~0.1-0.3)has rarely been studied.Here,we use DC/AC magnetization and(quasi)elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe_(1.07)Te_(0.8)Se_(0.2) sample.The AC-frequency dependent spin-freezing temperature T_(f) generates a frequency sensitivityΔT_(f)(ω)/[T_(f)(ω)Δlog_(10)ω]≈0.028 and the description of the critical slowing down withτ=τ0(T_(f)/T_(SG-1))^(-zv) gives T_(SG)≈22 K and zv≈10,comparable to that of a classical spin-glass system.We have also extended the frequency-dependent T_(f) to the smaller time scale using energy-resolution-dependent neutron diffraction measurements,in which the T_(N) of the short-range magnetic order increases systematically with increasing energy resolution.By removing the excess iron through annealing in oxygen,the spin-freezing behavior disappears,and bulk superconductivity is realized.Thus,the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity.展开更多
The vortex pinning determining the current carrying capacity of a superconductor is an important property to the applications of superconducting materials.For layered superconductors,the vortex pinning can be enhanced...The vortex pinning determining the current carrying capacity of a superconductor is an important property to the applications of superconducting materials.For layered superconductors,the vortex pinning can be enhanced by a strong interlayer interaction in accompany with a suppression of superconducting anisotropy,which remains to be investigated in iron based superconductors(FeSCs)with the layered structure.Here,based on the transport and magnetic torque measurements,we experimentally investigate the vortex pinning in two bilayer FeSCs,CaKFe_(4)As_(4)(Fe1144)and KCa_(2)Fe_(4)As4F_(2)(Fe12442),and compare their superconducting anisotropyγ.While the anisotropyγ≈3 for Fe1144 is much smaller thanγ≈15 in Fe12442 around Tc,a higher flux pinning energy as evidenced by a higher critical current density is found in Fe1144,as compared with the case of Fe12442.In combination with the literature data of Ba_(0.72)K_(0.28)Fe2As_(2) and Nd Fe As_(O0.82)F_(0.18),we reveal an anti-correlation between the pinning energy and the superconducting anisotropy in these Fe SCs.Our results thus suggest that the interlayer interaction can not be neglected when considering the vortex pinning in Fe SCs.展开更多
We systematically investigate the magnetic properties of Cu4-xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation(μSR) techniques.Neutron-diffraction measurements suggest that the longrang...We systematically investigate the magnetic properties of Cu4-xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation(μSR) techniques.Neutron-diffraction measurements suggest that the longrange magnetic order and the orthorhombic nuclear structure in the x=0 sample can persist up to x=0.23 and 0.43,respectively.The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures,TA0 and Tλ,which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation,respectively.Comparison between TA0 and TM from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to x=0.82.On the other hand,the doping level where Tλ becomes zero is about 0.66,which is much higher than threshold of the long-range order,i.e.,~0.4.Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above x=0.66 with the perfect kagome planes.展开更多
The van der Waals cluster magnet Nb_(3)Cl_(8)has recently been shown to possibly host a quantum-spin-liquid ground state.The Nb ions in this compound form a breathing kagome structure,where the magnetic moment comes f...The van der Waals cluster magnet Nb_(3)Cl_(8)has recently been shown to possibly host a quantum-spin-liquid ground state.The Nb ions in this compound form a breathing kagome structure,where the magnetic moment comes from three nearest Nb ions forming a molecular cluster with spin 1/2.Previous bulk measurements including magnetic susceptibility and specific heat suggested the existence of spinon Fermi surfaces.Here we further probe the spin system by nuclear magnetic resonance(NMR)and muon spin rotation and relaxation(μSR)techniques.We confirm that there is no magnetic long-range order and the dynamical spin fluctuations persist down to 0.075 K.These results provide further evidence that Nb_(3)Cl_(8)may host a quantum spin liquid.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1403900,2021YFA1401800,2018YFA0704201,and 2023YFA1406103)the National Natural Science Foundation of China(Grant Nos.U2032214,12122414,12104487,and 12004419)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB25000000)。
文摘The stability of superconductivity in superconductors is widely recognized to be determined by various factors,including charge,spin,orbit,lattice,and other related degrees of freedom.Here,we report our findings on the pressure-induced coevolution of superconductivity and Hall coefficient in KCa_(2)Fe_(4)As_(24F_(2),an iron-based superconductor possessing a hybrid crystal structure combining KFe_(2)As_(2) and CaFeAsF.Our investigation,involving high-pressure resistance,Hall effect and x-ray diffraction(XRD) measurements,allows us to observe the connection of the superconductivity and Hall coefficient with the anisotropic lattice shrinkage.We find that its ambient-pressure tetragonal(T) phase presents a collapse starting at around 18 GPa,where the sign of the Hall coefficient(R_(H)) changes from positive to negative.Upon further compression,both superconducting transition temperature(T_(c)) and R_(H) exhibit a monotonous decrease.At around 41 GPa,the superconductivity is completely suppressed(T_(c)=0),where the parameter a begins to decline again and the Hall coefficient remains nearly unchanged.Our experiment results clearly demonstrate that the pressure-induced anisotropic lattice collapse plays a crucial role in tuning the interplay among multiple degrees of freedom in the superconducting system and,correspondingly,the stability of the superconductivity.
基金supported by the National Natural Science Foundation of China(Grant Nos.11774303 and 11574373)the National Key Research and Development Program of China(Grant Nos.2022YFA1403402,2021YFA1400401,and 2020YFA0406003)+1 种基金the Chinese Academy of Sciences(Grant Nos.XDB33000000 and GJTD-2020-01)financial support from the Joint Fund of Yunnan Provincial Science and Technology Department(Grant No.2019FY003008)。
文摘We report on soft c-axis point-contact Andreev reflection(PCAR)spectroscopy combining with resistivity measurements on BaFe_(2)(As_(0.7)P_(0.3))_(2),to elucidate the superconducting gap structure in the vicinity of the quantum critical point.A double peak at the gap edge plus a dip feature at zero-bias has been observed on the PCAR spectra,indicative of the presence of a nodeless gap in BaFe_(2)(As_(0.7)P_(0.3))_(2).Detailed analysis within a sophisticated theoretical model reveals an anisotropic gap with deep gap minima.The PCARs also feature additional structures related to the electron-bosonic coupling mode.Using the extracted superconducting energy gap value,a characteristic bosonic energy Ω_(b) and its temperature dependence are obtained,comparable with the spin-resonance energy observed in neutron scattering experiment.These results indicate a magnetism-driven quantum critical point in the BaFe_(2)(As_(1-x)P_(x))_(2) system.
基金Supported by the National Basic Research Program of China under Grant Nos 2011CBA00100 and 2012CB821404the Project of International Team on Superconductivity and Novel Electronic Materials of Chinese Academy of Sciences
文摘We report a systematic investigation on c-axis point-contact Andreev reflection （PCAR） in BaFe2-xNixAs2 superconducting single crystals from underdoped to overdoped regions （0.075≤ x ≤0.15）. At low temperatures, an in-gap sharp peak at low-bias voltage is observed in PCAR for overdoped samples, in contrast to the case of underdoped junctions, in which an in-gap plateau is observed. The variety of the conductance spectra with doping can be well described by using a generalized Blonder-Tinkham-Klapwijk formalism with an angle-dependent gap. This gap shows a clear crossover from a nodeless in the underdoped side to a nodal feature in the overdoped region. This result provides evidence of the doping-induced evolution of the superconducting order parameter when the inter-pocket and intra-pocket scattering are tuned through doping, as expected in the s± scenario.
基金Supported by the National Natural Science Foundation of China(Grant Nos.51875009 and 51705006)the Key Project of Beijing Municipal Natural Science Foundation and Beijing Education Committee’s Science and Technology Plan(Grant Nos.KZ201710005004 and KZ201810005001)。
文摘We use femtosecond time-resolved optical reflectivity to study the photoexcited quasiparticle(QP)dynamics in the iron-based 112 type superconducting(SC)samples Ca0.82La0.18Fe1-xNixAs2,with x=0 and 0.024.In the parent sample,a fast and a slow relaxation emerge at temperatures below the magnetic-structure(MS)transition Tms≈50 K and the SC transition Tc≈33 K,respectively.The latter obviously corresponds to an SC QP dynamics,which is further confirmed in the x=0.024 sample with Tc≈25 K.The former suggests that a partial of photoexcited QP relaxation through a pesudogap(PG)channel,which is absent in the doped x=0.024 sample without the MS transition.
基金Project supported by the National Natural Science Foundation of China(Grant No.11004106)the National Basic Research Program of China(Grant No.2015CB946502)+1 种基金the Chinese Academy of Sciences(Grant No.SPRP-B:XDB25000000)the Youth Innovation Promotion Association of Chinese Academy of Sciences
文摘Complex permittivity and electrical impedance have been measured along the c-axis in single crystals BaFe_2 As_2,which are the conductors known as the parent compound of 122-type iron superconductor. The resultant relative errors defined in the study indicate the existence of the transformation between complex permittivity and electrical impedance in the conductors, and these two physics quantities possibly reveal different aspects of the consistent superconductivityrelevant physics picture.
基金Supported by the National Key Research and Development Program of China (Grant Nos.2016YFA0300300,2017YFA0302900,2018YFA0704200 and 2019YFA0308000)the National Natural Science Foundation of China (Grant Nos.11888101,11922414 and11874405)+2 种基金the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No.XDB25000000)the Youth Innovation Promotion Association of CAS (Grant No.2017013)the Research Program of Beijing Academy of Quantum Information Sciences (Grant No.Y18G06)。
文摘High resolution angle-resolved photoemission spectroscopy(ARPES)measurements are carried out on CaKFe_4 As_4,KCa_2 Fe_4 As_4 F_2 and(Ba_(0.6)K_(0.4))Fe_2 As_2 superconductors.Clear evidence of band folding between the Brillouin zone center and corners with a(π,π)wave vector has been found from the measured Fermi surface and band structures in all the three kinds of superconductors.A dominant √2×√2 surface reconstruction is observed on the cleaved surface of CaKFe_4As_4 by scanning tunneling microscopy(STM)measurements.We propose that the commonly observed √2×√2 reconstruction in the FeAs-based superconductors provides a general scenario to understand the origin of the(π,π)band folding.Our observations provide new insights in understanding the electronic structure and superconductivity mechanism in iron-based superconductors.
基金Project supported by the Science Fonds from the Ministry of Science and Technology of China(Grant Nos.2017YFA0302903,017YFA0303103,2016YFA0300502,and 2015CB921302)the National Natural Science Foundation of China(Grant Nos.11674406 and 11674372)+1 种基金the“Strategic Priority Research Program(B)”of the Chinese Academy of Sciences(Grant Nos.XDB07020300 and XDB07020200)the Youth Innovation Promotion Association of the Chinese Academy of Sciences
文摘Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr1 _xBaxFel.97Nio.03As2, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Srl xBaxFe2As2 is determined by the strength of the magnetic-elastic coupling.
基金supported by the National Basic Research Program of China(Grant Nos.2012CB821400,2012CB921302,and 2015CB921303)the National Natural Science Foundation of China(Grant Nos.11274237,91121004,51228201,11004238,and 11374011)
文摘We present magnetotransport studies on a series of BaFe2_xNixAs2 （0.03 〈 x 〈 0.10） single crystals. In the un- derdoped （x = 0.03） non-superconducting sample, the temperature-dependent resistivity exhibits a peak at 22 K, which is associated with the onset of filamentary superconductivity （FLSC）. FLSC is suppressed by an external magnetic field in a manner similar to the suppression of bulk superconductivity in an optimally-doped （x = 0.10） compound, suggesting the same possible origin as the bulk superconductivity. Our magnetoresistivity measurements reveal that FLSC persists up to the optimal doping and disappears in the overdoped regime where the long-range antiferromagnetic order is completely suppressed, pointing to a close relation between FLSC and the magnetic order.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB07020300)the National Basic Research Program of China(Grant Nos.2012CB821400 and 2011CBA00110)the National Natural Science Foundation of China(Grant Nos.11374011,11374346,and 11305257)
文摘We have studied the angular magnetoresistance of iron pnictides BaFe_（2-x）Ni_xAs_2, which shows clear 180 degree periodicity as fitted by a cosine function. In the x = 0.065 sample, the phase of the two-fold symmetry changes 90 degrees above the tetragonal-to-orthorhombic structural transition temperature Ts. Since the phase at low temperature is associated with the rotation of orthorhombic domains by magnetic field, we show that even vacuum grease can push the presence of orthorhombic domains at temperatures much higher than Ts. Our results suggest that residual stress may have significant effects in studying the nematic orders and its fluctuations in iron pnictides.
基金Beijing Normal University is supported by the National Natural Science Foundation of China (Grant Nos. 11734002 and 11922402, X.L.)supported by the US Department of Energy (DOE),Basic Energy Sciences (BES),under Contract No. DE-SC0012311 (P.D.)
文摘The iron-chalcogenide superconductor FeTe_(1-x)Se_(x) displays a variety of exotic features distinct from iron pnictides.Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x=0.5,the existence of a spin glass phase with short-range magnetic order in the doping range(x~0.1-0.3)has rarely been studied.Here,we use DC/AC magnetization and(quasi)elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe_(1.07)Te_(0.8)Se_(0.2) sample.The AC-frequency dependent spin-freezing temperature T_(f) generates a frequency sensitivityΔT_(f)(ω)/[T_(f)(ω)Δlog_(10)ω]≈0.028 and the description of the critical slowing down withτ=τ0(T_(f)/T_(SG-1))^(-zv) gives T_(SG)≈22 K and zv≈10,comparable to that of a classical spin-glass system.We have also extended the frequency-dependent T_(f) to the smaller time scale using energy-resolution-dependent neutron diffraction measurements,in which the T_(N) of the short-range magnetic order increases systematically with increasing energy resolution.By removing the excess iron through annealing in oxygen,the spin-freezing behavior disappears,and bulk superconductivity is realized.Thus,the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity.
基金Project supported by the National Natural Science Foundation of China(Grant No.11574338)the National Natural Science Foundation of China–China Academy of Engineering Physics NSAF Joint Fund(Grant No.U1530402)+4 种基金supported by the Superconducting Electronics Facility(SELF)of Shanghai Institute of Microsystem and Information Technology.The work at IOPCAS was supported by the National Key Research and Development Program of China(Grant No.2018YFA0704200)the National Natural Science Foundation of China(Grant Nos.11822411 and 11961160699)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(CAS)(Grant No.XDB25000000)the Youth Innovation Promotion Association of CAS(Grant No.2016004)。
文摘The vortex pinning determining the current carrying capacity of a superconductor is an important property to the applications of superconducting materials.For layered superconductors,the vortex pinning can be enhanced by a strong interlayer interaction in accompany with a suppression of superconducting anisotropy,which remains to be investigated in iron based superconductors(FeSCs)with the layered structure.Here,based on the transport and magnetic torque measurements,we experimentally investigate the vortex pinning in two bilayer FeSCs,CaKFe_(4)As_(4)(Fe1144)and KCa_(2)Fe_(4)As4F_(2)(Fe12442),and compare their superconducting anisotropyγ.While the anisotropyγ≈3 for Fe1144 is much smaller thanγ≈15 in Fe12442 around Tc,a higher flux pinning energy as evidenced by a higher critical current density is found in Fe1144,as compared with the case of Fe12442.In combination with the literature data of Ba_(0.72)K_(0.28)Fe2As_(2) and Nd Fe As_(O0.82)F_(0.18),we reveal an anti-correlation between the pinning energy and the superconducting anisotropy in these Fe SCs.Our results thus suggest that the interlayer interaction can not be neglected when considering the vortex pinning in Fe SCs.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0302900,2016YFA0300500,2018YFA0704200,2017YFA0303100,and 2016YFA0300600)the National Natural Science Foundation of China(Grant Nos.11874401,11674406,11674372,11961160699,11774399,12061130200,11974392,and 11822411)+4 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant Nos.XDB25000000,XDB07020000,XDB33000000,and XDB28000000)the Beijing Natural Science Foundation(Grant Nos.Z180008 and JQ19002)Guangdong Introducing Innovative and Entrepreneurial Teams(Grant No.2017ZT07C062)the Youth Innovation Promotion Association of CAS(Grant No.2016004)the Royal Society-Newton Advanced Fellowship(Grant No.NAF∖R1∖201248).
文摘We systematically investigate the magnetic properties of Cu4-xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation(μSR) techniques.Neutron-diffraction measurements suggest that the longrange magnetic order and the orthorhombic nuclear structure in the x=0 sample can persist up to x=0.23 and 0.43,respectively.The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures,TA0 and Tλ,which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation,respectively.Comparison between TA0 and TM from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to x=0.82.On the other hand,the doping level where Tλ becomes zero is about 0.66,which is much higher than threshold of the long-range order,i.e.,~0.4.Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above x=0.66 with the perfect kagome planes.
基金supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1403800,2022YFA1403400,2021YFA1400400,2023YFA1406100,and 2024YFA1409200)the National Natural Science Foundation of China(Grant Nos.12274444,12374142,and 12304170)+1 种基金the Chinese Academy of Sciences President’s International Fellowship Initiative(Grant No.2025PG0007)We thank ISIS Facility for beam time(Grant No.RB2310088).
文摘The van der Waals cluster magnet Nb_(3)Cl_(8)has recently been shown to possibly host a quantum-spin-liquid ground state.The Nb ions in this compound form a breathing kagome structure,where the magnetic moment comes from three nearest Nb ions forming a molecular cluster with spin 1/2.Previous bulk measurements including magnetic susceptibility and specific heat suggested the existence of spinon Fermi surfaces.Here we further probe the spin system by nuclear magnetic resonance(NMR)and muon spin rotation and relaxation(μSR)techniques.We confirm that there is no magnetic long-range order and the dynamical spin fluctuations persist down to 0.075 K.These results provide further evidence that Nb_(3)Cl_(8)may host a quantum spin liquid.
