What factors fundamentally determine the value of superconducting transition temperature Tc in high temperature superconductors has been the subject of intense debate.Following the establishment of an empirical law kn...What factors fundamentally determine the value of superconducting transition temperature Tc in high temperature superconductors has been the subject of intense debate.Following the establishment of an empirical law known as Homes'law,there is a growing consensus in the community that the Tc value of the cuprate superconductors is closely linked to the superfluid density(ρ_(s))of its ground state and the conductivity(σ)of its normal state.However,all the data supporting this empirical law(ρ_(s)=AσT_(c))have been obtained from the ambientpressure superconductors.In this study,we present the first high-pressure results about the connection of the quantities of ρ_(s) and σ with T_(c),through the studies on the Bi_(1.74)Pb_(0.38)Sr_(1.88)CuO_(6+δ)and Bi_(2)Sr_(2)CaCu_(2)O_(8+δ),in which the value of their high-pressure resistivity(ρ=1/σ)is achieved by adopting our newly established method,while the quantity ofρs is extracted using Homes'law.We highlight that the Tc values are strongly linked to the joint response factors of magnetic field and electric field,i.e.,ρ_(s) and σ,respectively,implying that the physics determining T_(c) is governed by the intrinsic electromagnetic fields of the system.展开更多
Mn_(3)Sn_(2)has been proposed as an ideal material for magnetic refrigeration.It undergoes two successive ferromagnetic transitions(T_(C1)=262 K and T_(C2)=227 K)and one antiferromagnetic transition(TN=192 K).Herein w...Mn_(3)Sn_(2)has been proposed as an ideal material for magnetic refrigeration.It undergoes two successive ferromagnetic transitions(T_(C1)=262 K and T_(C2)=227 K)and one antiferromagnetic transition(TN=192 K).Herein we report,for the first time,the preparation of single crystals of Mn_(3)Sn_(2)from Bi flux.The resultant anisotropic magnetic properties and magnetocaloric effect are investigated along the three principal crystallographic directions of the crystal.Significant anisotropy of magnetic susceptibility and multiple field-induced metamagnetic transitions were found at low fields,whereas the magnetocaloric effect was found to be almost isotropic and larger than that of the polycrystalline one.The maximum magnetic entropy change amounts to-ΔSM=4.01 J·kg^(-1)·K^(-1)near T_(C1)under a magnetic field change of μ_(0)ΔH=5 T along the c-axis,with the corresponding refrigerant capacity of 1750 mJ·cm^(-3).Combined with a much wider cooling temperature span(~80 K),our results demonstrate Mn_(3)Sn_(2)single crystal to be an attractive candidate working material for active magnetic refrigeration at low temperatures.展开更多
We report 75As-nuclear magnetic resonance(NMR)and nuclear quadrupole resonance(NQR)measurements on transition-metal arsenides LaRu2As2,KCa2Fe4As4F2,and A2Cr3As3.In the superconducting state of LaRu2As2,a Hebel–Slicht...We report 75As-nuclear magnetic resonance(NMR)and nuclear quadrupole resonance(NQR)measurements on transition-metal arsenides LaRu2As2,KCa2Fe4As4F2,and A2Cr3As3.In the superconducting state of LaRu2As2,a Hebel–Slichter coherence peak is found in the temperature dependence of the spin-lattice relaxation rate 1/T1 just below Tc,which indicates that LaRu2As2 is a full-gap superperconducor.For KCa2Fe4As4F2,antiferromagnetic spin fluctuations are observed in the normal state.We further find that the anisotropy rate RAF=Tc 1/Tab 1 is small and temperature independent,implying that the low energy spin fluctuations are isotropic in spin space.Our results indicate that KCa2Fe4As4F2 is a moderately overdoped iron-arsenide high-temperature superconductor with a stoichiometric composition.For A2Cr3As3(A=Na,K,Rb,Cs),we calculate the electric field gradient by first-principle method and assign the 75As-NQR peaks to two crystallographically different As sites,paving the way for further NMR investigation.展开更多
We develop an experimental tool to investigate the order parameter of superconductors by combining pointcontact spectroscopy measurement with high-pressure technique.It is demonstrated for the first time that planar p...We develop an experimental tool to investigate the order parameter of superconductors by combining pointcontact spectroscopy measurement with high-pressure technique.It is demonstrated for the first time that planar point-contact spectroscopy measurement on noncentrosymmetric superconducting PbTaSe2 single crystals is systematically subjected to hydrostatic pressures up to 12.1 kbar.Under such a high pressure,the normal-state contact resistance is sensitive to the applied pressure,reflecting the underlying variation of contact transparency upon pressures.In a superconducting state,the pressure dependence of the energy gap△0 and the critical temperature Tc for gap opening/closing are extracted based on a generalized Blond-Tinkham-Klapwijk model.The gap ratio 2△0/kB Tc indicates a crossover from weak coupling to strong coupling in electron pairing strength upon pressure for PbTaSe2.Our experimental results show the accessibility and validity of high-pressure pointcontact spectroscopy,offering rich information about high-pressure superconductivity.展开更多
We report the magnetoresistance(MR), de Haas-van Alphen(dHvA) effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field,...We report the magnetoresistance(MR), de Haas-van Alphen(dHvA) effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field, a metal-to-insulator-like transition in ρ(T) and a nonsaturating MR are observed at low temperatures. The dHvA oscillations reveal a small Fermi-surface pocket with a nontrivial Berry phase. The analysis of the nonlinear Hall resistivity shows that TiSi is a multiband system with low carrier densities and high mobilities. All these results unambiguously prove the existence of Dirac fermions in TiSi.展开更多
We investigate the interface between a three-dimensional Dirac semimetal Cd3As2 and a normal metal via softpoint contact spectroscopy measurement.The superconducting gap features were detected below 3.8 K and 7.1 K in...We investigate the interface between a three-dimensional Dirac semimetal Cd3As2 and a normal metal via softpoint contact spectroscopy measurement.The superconducting gap features were detected below 3.8 K and 7.1 K in the case of Cd3As2 single crystals sputter-coated with the Pt and Au films,respectively,in the differential conductance dI/dV-V plots of the point contacts.As the applied magnetic field increased,the drop in the zerobias contact resistance shifted toward lower temperatures.The topologically non-trivial band structure of Cd3As2 is considered to play a crucial role in inducing the superconductivity.Apart from realizing superconductivity in topological materials,our creative approach can be used to investigate possible topological superconductivity and exhibits a high application potential in electronic devices.展开更多
The discovery of EuFeAs_(2),currently the only charge-neutral parent phase of the 112-type iron-pnictide system,provides a new platform for the study of elemental doping effects on magnetism and superconductivity(SC)....The discovery of EuFeAs_(2),currently the only charge-neutral parent phase of the 112-type iron-pnictide system,provides a new platform for the study of elemental doping effects on magnetism and superconductivity(SC).In this study,a series of polycrystalline EuFe_(1-y)Co_(y)As_(2)and Eu_(0.9)Pr_(0.1)Fe_(1-y)Co_(y)As_(2)samples are synthesized through solid-state reaction,and the evolutions of SC and magnetism with Co doping in EuFeAs_(2)and Eu_(0.9)Pr_(0.1)FeAs_(2)are investigated by electrical transport and magnetic susceptibility measurements.For EuFe_(1-y)Co_(y)As_(2),the Eu-related antiferromagnetic(AFM)transition around 40 K is barely affected by Co doping,while the Fe-related spin density wave(SDW)transition temperature drops rapidly.Meanwhile,SC is induced by a trace amount of Co doping,with a highest transition temperature T_(c)~28 K found in EuFe0.9Co0.1As_(2).For the Eu_(0.9)Pr_(0.1)Fe1-yCo_(y)As_(2)series,the magnetism and superconductivity show similar evolutions upon Co doping,and the highest T_(c)is enhanced to 30.6 K with an optimum doping level y~0.07.Our results shed light on the competition between SC and SDW with Co doping in the 112-type EuFeAs_(2)system.展开更多
Since the discovery of superconductivity in LaFeAsO1-xFx, the high-Tc iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8].However,the mechanism of the uncon...Since the discovery of superconductivity in LaFeAsO1-xFx, the high-Tc iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8].However,the mechanism of the unconventional superconductivity is still to be resolved.To address such issues,numerous 3d,4d,5d transition metal pnietide,silicide,germanide,chalcogenide materials crystalizing in the similar crystal structure with iron pnictide/ selenide suoerconductors were studied [9-24].展开更多
基金supported by the National Key Research and Development Program of China(Grant Nos.2021YFA1401800 and 2022YFA1403900)the National Natural Science Foundation of China(Grant Nos.U2032214,12122414,12104487,and 12004419)+1 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB25000000)supported by the US Department of Energy,Office of Basic Energy Sciences(Grant No.DOE-sc0012704)。
文摘What factors fundamentally determine the value of superconducting transition temperature Tc in high temperature superconductors has been the subject of intense debate.Following the establishment of an empirical law known as Homes'law,there is a growing consensus in the community that the Tc value of the cuprate superconductors is closely linked to the superfluid density(ρ_(s))of its ground state and the conductivity(σ)of its normal state.However,all the data supporting this empirical law(ρ_(s)=AσT_(c))have been obtained from the ambientpressure superconductors.In this study,we present the first high-pressure results about the connection of the quantities of ρ_(s) and σ with T_(c),through the studies on the Bi_(1.74)Pb_(0.38)Sr_(1.88)CuO_(6+δ)and Bi_(2)Sr_(2)CaCu_(2)O_(8+δ),in which the value of their high-pressure resistivity(ρ=1/σ)is achieved by adopting our newly established method,while the quantity ofρs is extracted using Homes'law.We highlight that the Tc values are strongly linked to the joint response factors of magnetic field and electric field,i.e.,ρ_(s) and σ,respectively,implying that the physics determining T_(c) is governed by the intrinsic electromagnetic fields of the system.
基金supported by the National Natural Science Foundation of China(Grant No.12274440)the Strategic Priority Research Program(B)of Chinese Academy of Sciences(Grant No.XDB33010100)National Key R&D Program of China(Grant No.2022YFA1403903)。
文摘Mn_(3)Sn_(2)has been proposed as an ideal material for magnetic refrigeration.It undergoes two successive ferromagnetic transitions(T_(C1)=262 K and T_(C2)=227 K)and one antiferromagnetic transition(TN=192 K).Herein we report,for the first time,the preparation of single crystals of Mn_(3)Sn_(2)from Bi flux.The resultant anisotropic magnetic properties and magnetocaloric effect are investigated along the three principal crystallographic directions of the crystal.Significant anisotropy of magnetic susceptibility and multiple field-induced metamagnetic transitions were found at low fields,whereas the magnetocaloric effect was found to be almost isotropic and larger than that of the polycrystalline one.The maximum magnetic entropy change amounts to-ΔSM=4.01 J·kg^(-1)·K^(-1)near T_(C1)under a magnetic field change of μ_(0)ΔH=5 T along the c-axis,with the corresponding refrigerant capacity of 1750 mJ·cm^(-3).Combined with a much wider cooling temperature span(~80 K),our results demonstrate Mn_(3)Sn_(2)single crystal to be an attractive candidate working material for active magnetic refrigeration at low temperatures.
基金National Natural Science Foundation of China(Grant Nos.11674377,11634015,and 11974405)the National Key R&D Program of China(Grant Nos.2017YFA0302904 and 2016YFA0300502)J.Y.also acknowledges support by the Youth Innovation Promotion Association of Chinese Academy of Sciences.
文摘We report 75As-nuclear magnetic resonance(NMR)and nuclear quadrupole resonance(NQR)measurements on transition-metal arsenides LaRu2As2,KCa2Fe4As4F2,and A2Cr3As3.In the superconducting state of LaRu2As2,a Hebel–Slichter coherence peak is found in the temperature dependence of the spin-lattice relaxation rate 1/T1 just below Tc,which indicates that LaRu2As2 is a full-gap superperconducor.For KCa2Fe4As4F2,antiferromagnetic spin fluctuations are observed in the normal state.We further find that the anisotropy rate RAF=Tc 1/Tab 1 is small and temperature independent,implying that the low energy spin fluctuations are isotropic in spin space.Our results indicate that KCa2Fe4As4F2 is a moderately overdoped iron-arsenide high-temperature superconductor with a stoichiometric composition.For A2Cr3As3(A=Na,K,Rb,Cs),we calculate the electric field gradient by first-principle method and assign the 75As-NQR peaks to two crystallographically different As sites,paving the way for further NMR investigation.
基金Supported by the National Science Foundation of China(Grant Nos.11574373 and 11774303)the Joint Fund of Yunnan Provincial Science and Technology Department(Grant No.2019FY003008)。
文摘We develop an experimental tool to investigate the order parameter of superconductors by combining pointcontact spectroscopy measurement with high-pressure technique.It is demonstrated for the first time that planar point-contact spectroscopy measurement on noncentrosymmetric superconducting PbTaSe2 single crystals is systematically subjected to hydrostatic pressures up to 12.1 kbar.Under such a high pressure,the normal-state contact resistance is sensitive to the applied pressure,reflecting the underlying variation of contact transparency upon pressures.In a superconducting state,the pressure dependence of the energy gap△0 and the critical temperature Tc for gap opening/closing are extracted based on a generalized Blond-Tinkham-Klapwijk model.The gap ratio 2△0/kB Tc indicates a crossover from weak coupling to strong coupling in electron pairing strength upon pressure for PbTaSe2.Our experimental results show the accessibility and validity of high-pressure pointcontact spectroscopy,offering rich information about high-pressure superconductivity.
基金Supported by the National Key Research Program of China under Grant Nos 2016YFA0401000 and 2016YFA0300604the National Basic Research Program of China under Grant No 2015CB921303+1 种基金the Strategic Priority Research Program(B)of Chinese Academy of Sciences under Grant No XDB07020100the National Natural Science Foundation of China under Grant No11874417
文摘We report the magnetoresistance(MR), de Haas-van Alphen(dHvA) effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field, a metal-to-insulator-like transition in ρ(T) and a nonsaturating MR are observed at low temperatures. The dHvA oscillations reveal a small Fermi-surface pocket with a nontrivial Berry phase. The analysis of the nonlinear Hall resistivity shows that TiSi is a multiband system with low carrier densities and high mobilities. All these results unambiguously prove the existence of Dirac fermions in TiSi.
基金Supported by the National Natural Science Foundation of China(Grant Nos.11704403 and 11874417)the National Key Research Program of China(Grant Nos.2016YFA0401000,2016YFA0300604,and 2018YFA070112)the Strategic Priority Research Program(B)of Chinese Academy of Sciences(Grant No.XDB33010100)。
文摘We investigate the interface between a three-dimensional Dirac semimetal Cd3As2 and a normal metal via softpoint contact spectroscopy measurement.The superconducting gap features were detected below 3.8 K and 7.1 K in the case of Cd3As2 single crystals sputter-coated with the Pt and Au films,respectively,in the differential conductance dI/dV-V plots of the point contacts.As the applied magnetic field increased,the drop in the zerobias contact resistance shifted toward lower temperatures.The topologically non-trivial band structure of Cd3As2 is considered to play a crucial role in inducing the superconductivity.Apart from realizing superconductivity in topological materials,our creative approach can be used to investigate possible topological superconductivity and exhibits a high application potential in electronic devices.
基金supported by the National Natural Science Foundation of China (12141002,52088101,11874417,11974389,and 52172216)the Ministry of Science and Technology of China (2021YFA0718702)+5 种基金the Chinese Academy of Sciences through the Strategic Priority Research Programthe Scientific Instrument Developing Programthe Project for Young Scientists in Basic Research (XDB33000000,YJKYYQ20200017,and YSBR-057)the Chinese Postdoctoral Science Foundation (E0BK181)the funding support of the National Key Research and Development Program of China (2018YFA0702100)the support from the Key Research Project of Zhejiang Laboratory (2021PE0AC02)。
基金supported by the National Natural Science Foundation of China(Grant No.11774402)the National Key Research Program of China(Grant Nos.2018YFA0704200,and 2016YFA0300301)。
文摘The discovery of EuFeAs_(2),currently the only charge-neutral parent phase of the 112-type iron-pnictide system,provides a new platform for the study of elemental doping effects on magnetism and superconductivity(SC).In this study,a series of polycrystalline EuFe_(1-y)Co_(y)As_(2)and Eu_(0.9)Pr_(0.1)Fe_(1-y)Co_(y)As_(2)samples are synthesized through solid-state reaction,and the evolutions of SC and magnetism with Co doping in EuFeAs_(2)and Eu_(0.9)Pr_(0.1)FeAs_(2)are investigated by electrical transport and magnetic susceptibility measurements.For EuFe_(1-y)Co_(y)As_(2),the Eu-related antiferromagnetic(AFM)transition around 40 K is barely affected by Co doping,while the Fe-related spin density wave(SDW)transition temperature drops rapidly.Meanwhile,SC is induced by a trace amount of Co doping,with a highest transition temperature T_(c)~28 K found in EuFe0.9Co0.1As_(2).For the Eu_(0.9)Pr_(0.1)Fe1-yCo_(y)As_(2)series,the magnetism and superconductivity show similar evolutions upon Co doping,and the highest T_(c)is enhanced to 30.6 K with an optimum doping level y~0.07.Our results shed light on the competition between SC and SDW with Co doping in the 112-type EuFeAs_(2)system.
基金supported by the National Natural Science Foundation of China(Grant Nos.11474339,and 11774402)the National Basic Research Program of China(Grant No.2016YFA0300301)and the Youth Innovation Promotion Association of the Chinese Academy of Sciences
文摘Since the discovery of superconductivity in LaFeAsO1-xFx, the high-Tc iron-based superconductors have been extensively studied from both experimental and theoretical viewpoints [1-8].However,the mechanism of the unconventional superconductivity is still to be resolved.To address such issues,numerous 3d,4d,5d transition metal pnietide,silicide,germanide,chalcogenide materials crystalizing in the similar crystal structure with iron pnictide/ selenide suoerconductors were studied [9-24].