Using angle-resolved photoemission spectroscopy and density functional theory calculations methods,we investigate the electronic structures and topological properties of ternary tellurides NbIrTe_(4),a candidate for t...Using angle-resolved photoemission spectroscopy and density functional theory calculations methods,we investigate the electronic structures and topological properties of ternary tellurides NbIrTe_(4),a candidate for type-II Weyl semimetal.We demonstrate the presence of several Fermi arcs connecting their corresponding Weyl points on both termination surfaces of the topological material.Our analysis reveals the existence of Dirac points,in addition to Weyl points,giving both theoretical and experimental evidences of the coexistence of Dirac and Weyl points in a single material.These findings not only confirm NbIrTe_(4) as a unique topological semimetal but also open avenues for exploring novel electronic devices based on its coexisting Dirac and Weyl fermions.展开更多
Pressure induced insulator to metal transition followed by the appearance of superconductivity has been observed recently in inorganic quantum spin liquid candidate NaYbSe_(2).In this paper,we study the properties of ...Pressure induced insulator to metal transition followed by the appearance of superconductivity has been observed recently in inorganic quantum spin liquid candidate NaYbSe_(2).In this paper,we study the properties of isostructural compound NaYbS_(2)under pressure.It is found that the resistance of Na YbS_(2)single crystal exhibits an insulating state below 82.9 GPa,but with a drop of more than six orders of magnitude at room temperature.Then a minimum of resistance is observed at about 100.1 GPa and it moves to lower temperature with further compression.Finally,a metallic state in the whole temperature range is observed at about 130.3 GPa accompanied by a non-Fermi liquid behavior below 100 K.The insulator to metal transition,non-monotonic resistance feature and non-Fermi liquid behavior of NaYbS_(2)under pressure are similar to those of NaYbSe_(2),suggesting that these phenomena might be the universal properties in NaLnCh_(2)(Ln=rare earth,Ch=O,S,Se)system.展开更多
We report ^(121/123)Sb nuclear quadrupole resonance(NQR)and ^(51)V nuclear magnetic resonance(NMR)measurements on kagome metal CsV_(3)Sb_(5) with T_(c)=2.5 K.Both ^(51)V NMR spectra and ^(121/123)Sb NQR spectra split ...We report ^(121/123)Sb nuclear quadrupole resonance(NQR)and ^(51)V nuclear magnetic resonance(NMR)measurements on kagome metal CsV_(3)Sb_(5) with T_(c)=2.5 K.Both ^(51)V NMR spectra and ^(121/123)Sb NQR spectra split after a charge density wave(CDW)transition,which demonstrates a commensurate CDW state.The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first-order phase transition.At low temperature,electric-field-gradient fluctuations diminish and magnetic fluctuations become dominant.Superconductivity emerges in the charge order state.Knight shift decreases and 1/T_(1)T shows a Hebel–Slichter coherence peak just below T_(c),indicating that CsV_(3)Sb_(5) is an s-wave superconductor.展开更多
Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid(QSL), and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular...Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid(QSL), and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular lattice spin liquid candidate YbMgGaO_4 stimulated an increasing attention on the rare-earth-based frustrated magnets with strong spin-orbit coupling. Here we report the synthesis and characterization of a large family of rare-earth chalcogenides AReCh_2(A = alkali or monovalent ions, Re = rare earth, Ch = O,S,Se). The family compounds share the same structure(R3 m) as YbMgGaO_4,and antiferromagnetically coupled rare-earth ions form perfect triangular layers that are well separated along the c-axis. Specific heat and magnetic susceptibility measurements on NaYbO_2,NaYbS_2 and NaYbSe_2 single crystals and polycrystals, reveal no structural or magnetic transition down to 50 mK. The family, having the simplest structure and chemical formula among the known QSL candidates, removes the issue on possible exchange disorders in YbMgGaO_4. More excitingly, the rich diversity of the family members allows tunable charge gaps, variable exchange coupling, and many other advantages.This makes the family an ideal platform for fundamental research of QSLs and its promising applications.展开更多
We report the detailed physical properties of quaternary compound Ba2BiFeS5 with the key structural ingredient of isolated FeS4 tetrahedra.Magnetization and heat capacity measurements clearly indicate that Ba2BiFeS5 h...We report the detailed physical properties of quaternary compound Ba2BiFeS5 with the key structural ingredient of isolated FeS4 tetrahedra.Magnetization and heat capacity measurements clearly indicate that Ba2BiFeS5 has a paramagnetic to antiferromagnetic transition at about 30 K.The calculated magnetic entropy above ordering temperature is much smaller than theoretical value for high-spin Fe^3+ion with S=5/2,implying the possible short-range antiferromagnetic fluctuation in Ba2BiFeS5.展开更多
By using angle-resolvea photoemission spectroscopy(ARPES) combined with the first-principies electronic structure calculations,we report the quantized states at the surface of a single crystal 2 H-TaSe_(2).We have obs...By using angle-resolvea photoemission spectroscopy(ARPES) combined with the first-principies electronic structure calculations,we report the quantized states at the surface of a single crystal 2 H-TaSe_(2).We have observed sub-bands of quantized states at the three-dimensional Brillouin zone center due to a highly dispersive band with light effective mass along k_(z) direction.The quantized sub-bands shift upward towards E_(F) while the bulk band at Γ shifts downward with the decrease of temperature across charge density wave(CDW) formation.The band shifts could be intimately related to the CDW.While neither the two-dimensional Fermi-surface nesting nor purely strong electron-phonon coupling can explain the mechanism of CDW in 2 H-TaSe_(2),our experiment may ignite the interest in understanding the CDW mechanism in this family.展开更多
We performed high-pressure transport studies on the flat-band Kagome compounds,Pd_(3)P_(2)(S_(1−x)Se_(x))_(8)(x=0,0.25),with a diamond anvil cell.For both compounds,the resistivity exhibits an insulating behavior with...We performed high-pressure transport studies on the flat-band Kagome compounds,Pd_(3)P_(2)(S_(1−x)Se_(x))_(8)(x=0,0.25),with a diamond anvil cell.For both compounds,the resistivity exhibits an insulating behavior with pressure up to 17GPa.With pressure above 20GPa,a metallic behavior is observed at high temperatures in Pd_(3)P_(2)S_(8),and superconductivity emerges at low temperatures.The onset temperature of superconducting transition T_(C) rises monotonically from 2K to 4.8K and does not saturate with pressure up to 43GPa.For the Se-doped compound Pd_(3)P_(2)(S_(0.75)Se_(0.25))_(8),the T_(C) is about 1.5K higher than that of the undoped one over the whole pressure range,and reaches 6.4K at 43GPa.The upper critical field with field applied along the c axis at typical pressures is about 50%of the Pauli limit,suggesting a 3D superconductivity.The Hall coefficient in the metallic phase is low and exhibits a peaked behavior at about 30 K,which suggests either a multi-band electronic structure or an electron correlation effect in the system.展开更多
We report ^(121)Sb nuclear quadrupole resonance(NQR)measurements on kagome superconductor CsV_(3)Sb_(5) with Tc=2.5 K.^(121)Sb NQR spectra split after a charge density wave(CDW)transition at 94 K,which demonstrates a ...We report ^(121)Sb nuclear quadrupole resonance(NQR)measurements on kagome superconductor CsV_(3)Sb_(5) with Tc=2.5 K.^(121)Sb NQR spectra split after a charge density wave(CDW)transition at 94 K,which demonstrates a commensurate CDW state.The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first order phase transition.The CDW order exhibits tri-hexagonal deformation with a lateral shift between the adjacent kagome layers,which is consistent with 2×2×2 superlattice modulation.The superconducting state coexists with CDW order and shows a conventional s-wave behavior in the bulk state.展开更多
Two-dimensional van der Waals(2D vdW)magnets have attracted great attention recently and possess the unprecedented advantages of incorporating high-quality vdW heterostructures and homostructures into spintronic devic...Two-dimensional van der Waals(2D vdW)magnets have attracted great attention recently and possess the unprecedented advantages of incorporating high-quality vdW heterostructures and homostructures into spintronic devices,and exploring various physical phenomena or technologies.Among them,Fe_(5)GeTe_(2)(F5GT)has ferromagnetic order close to room temperature,however the magnetic properties near its intrinsic transitions and F5GT-based 2D devices remain mostly unexplored.Here,we systematically demonstrate the peculiar magnetic properties of Fe_(5)GeTe_(2)nanoflakes near its intrinsic transition temperature(Tp)which is far lower than its Curie temperature(TC)of~265 K,and firstly discover anomalous magnetoresistance effect in F5GT homo-junctions by magneto-transport measurements.The strongest anomalous Hall effect occurs around Tp which is located in a temperature range from 130 to 160 K for the F5GT nanoflakes with different thicknesses.Furthermore,negative magnetoresistance(N-MR)and butterfly-shaped magnetoresistance(B-MR)are observed in F5GT homo-junction devices,and they appeared only in an intermediate temperature range from 110 to 160 K,noticeably showing the maxima near the T_(p)rather than the lowest temperature.Our experimental results clearly reveal the significant influence of intrinsic transitions on magnetic properties of F5GT and magnetoresistance effect in F5GT homo-junction devices,which imply a new strategy to achieve highperformance 2D spintronic devices by tuning intrinsic magnetic or structural transitions in 2D vdW magnets.展开更多
We study the magnetocaloric effect (MCE) in van der Waals (vdW) crystal CrBr3.Bulk CrBr3 exhibits a second-order paramagnetic-ferromagnetic phase transition with TC =33 K.The maximum magnetic entropy change-△SM near ...We study the magnetocaloric effect (MCE) in van der Waals (vdW) crystal CrBr3.Bulk CrBr3 exhibits a second-order paramagnetic-ferromagnetic phase transition with TC =33 K.The maximum magnetic entropy change-△SM near TC is about 7.2 J.kg-1.K-1 with the maximum adiabatic temperature change △Tadmax =2.37 K and the relative cooling power RCP =191.5 J.kg-1 at μoH =5 T,all of which are remarkably larger than those in CrI3.These results suggest that the vdW crystal CrBr3 is a promising candidate for the low-dimensional magnetic refrigeration in low temperature region.展开更多
We have synthesized and investigated physical properties of two new quaternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals, which are isostructural to Tb2NiAl4Ge2 and Er2CoAl4Ge2. The most important structural f...We have synthesized and investigated physical properties of two new quaternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals, which are isostructural to Tb2NiAl4Ge2 and Er2CoAl4Ge2. The most important structural feature of these materials is the anti-CaF2-type CoAl4T2 slabs. These materials show metallic behavior below 300 K and there is a long-range antiferromagnetic (AFM) transition appearing at 20 and 27 K for GdCoAl4Ge2 and Gd2CoAl4Si2, respectively. Resistivity and heat capacity measurements also confirm these bulk AFM transitions. Further analysis indicates that this long-range antiferromagnetism should result from the magnetic interaction between local moments of Gd^3+ ions.展开更多
The CoSi family hosts unconventional topological nodes with nonzero Chern numbers.The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes.Here,using angle-re...The CoSi family hosts unconventional topological nodes with nonzero Chern numbers.The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes.Here,using angle-resolved photoemission spectroscopy,we have systematically investigated the(001)surface states of pristine and Ni-doped Co Si.The surface states form saddle-like band structures at/near the time-reversal invariant point near the Fermi level.The Fermi arcs undergo consecutive Lifshitz transitions at the saddle points X,leading to changes of the Fermi arc configuration.As the density of states has a van Hove singularity at the saddle points,exotic many-body physical phenomena may emerge accompanied by the topological transitions of surface Fermi arcs.展开更多
The recent discovery of superconductivity up to 32 K in the pressurized MoBreignites the interest in exploring high-Tc superconductors in transition-metal diborides. Inspired by that work, we turn our attention to the...The recent discovery of superconductivity up to 32 K in the pressurized MoBreignites the interest in exploring high-Tc superconductors in transition-metal diborides. Inspired by that work, we turn our attention to the 5 d transition-metal diborides.Here we systematically investigate the responses of both structural and physical properties of WBand ReBto external pressure,which possess different types of boron layers. Similar to MoB, the pressure-induced superconductivity was also observed in WBabove 60 GPa with a maximum Tcof 15 K at 100 GPa, while no superconductivity was detected in ReBin this pressure range. Interestingly, the structures at ambient pressure for both WBand ReBpersist to high pressure without structural phase transitions. Theoretical calculations suggest that the ratio of flat boron layers in this class of transition-metal diborides may be crucial for the appearance of high Tc. The combined theoretical and experimental results highlight the effect of the geometry of boron layers on superconductivity and shed light on the exploration of novel high-Tcsuperconductors in borides.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos.12274455,12274459,and 12204533)the National Key R&D Program of China (Grant No.2022YFA1403800)the Beijing Natural Science Foundation (Grant No.Z200005)。
文摘Using angle-resolved photoemission spectroscopy and density functional theory calculations methods,we investigate the electronic structures and topological properties of ternary tellurides NbIrTe_(4),a candidate for type-II Weyl semimetal.We demonstrate the presence of several Fermi arcs connecting their corresponding Weyl points on both termination surfaces of the topological material.Our analysis reveals the existence of Dirac points,in addition to Weyl points,giving both theoretical and experimental evidences of the coexistence of Dirac and Weyl points in a single material.These findings not only confirm NbIrTe_(4) as a unique topological semimetal but also open avenues for exploring novel electronic devices based on its coexisting Dirac and Weyl fermions.
基金the National Key Research and Development Program of China(Grant Nos.2018YFA0305700,2018YFE0202600,and 2022YFA1403800)the Beijing Natural Science Foundation(Grant Nos.2202059 and Z200005)+2 种基金the National Natural Science Foundation of China(Grant Nos.22171283 and 12274459)the Hebei Natural Science Foundation(Grant No.B2020205040)the Beijing National Laboratory for Condensed Matter Physics。
文摘Pressure induced insulator to metal transition followed by the appearance of superconductivity has been observed recently in inorganic quantum spin liquid candidate NaYbSe_(2).In this paper,we study the properties of isostructural compound NaYbS_(2)under pressure.It is found that the resistance of Na YbS_(2)single crystal exhibits an insulating state below 82.9 GPa,but with a drop of more than six orders of magnitude at room temperature.Then a minimum of resistance is observed at about 100.1 GPa and it moves to lower temperature with further compression.Finally,a metallic state in the whole temperature range is observed at about 130.3 GPa accompanied by a non-Fermi liquid behavior below 100 K.The insulator to metal transition,non-monotonic resistance feature and non-Fermi liquid behavior of NaYbS_(2)under pressure are similar to those of NaYbSe_(2),suggesting that these phenomena might be the universal properties in NaLnCh_(2)(Ln=rare earth,Ch=O,S,Se)system.
基金Supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0302901,2018YFE0202600,and 2016YFA0300504)the National Natural Science Foundation of China(Grant Nos.11921004,11634015,11822412,and 11774423)+1 种基金the Beijing Natural Science Foundation(Grant No.Z200005)the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.XDB33010100).
文摘We report ^(121/123)Sb nuclear quadrupole resonance(NQR)and ^(51)V nuclear magnetic resonance(NMR)measurements on kagome metal CsV_(3)Sb_(5) with T_(c)=2.5 K.Both ^(51)V NMR spectra and ^(121/123)Sb NQR spectra split after a charge density wave(CDW)transition,which demonstrates a commensurate CDW state.The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first-order phase transition.At low temperature,electric-field-gradient fluctuations diminish and magnetic fluctuations become dominant.Superconductivity emerges in the charge order state.Knight shift decreases and 1/T_(1)T shows a Hebel–Slichter coherence peak just below T_(c),indicating that CsV_(3)Sb_(5) is an s-wave superconductor.
基金Supported by the Ministry of Science and Technology of China under Grant Nos 2016YFA0300504,2017YFA0302904 and 2016YFA0301001the Natural Science Foundation of China under Grant Nos 11774419,11474357,11822412,11774423 and 11574394
文摘Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid(QSL), and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular lattice spin liquid candidate YbMgGaO_4 stimulated an increasing attention on the rare-earth-based frustrated magnets with strong spin-orbit coupling. Here we report the synthesis and characterization of a large family of rare-earth chalcogenides AReCh_2(A = alkali or monovalent ions, Re = rare earth, Ch = O,S,Se). The family compounds share the same structure(R3 m) as YbMgGaO_4,and antiferromagnetically coupled rare-earth ions form perfect triangular layers that are well separated along the c-axis. Specific heat and magnetic susceptibility measurements on NaYbO_2,NaYbS_2 and NaYbSe_2 single crystals and polycrystals, reveal no structural or magnetic transition down to 50 mK. The family, having the simplest structure and chemical formula among the known QSL candidates, removes the issue on possible exchange disorders in YbMgGaO_4. More excitingly, the rich diversity of the family members allows tunable charge gaps, variable exchange coupling, and many other advantages.This makes the family an ideal platform for fundamental research of QSLs and its promising applications.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0300504)the National Natural Science Foundation of China(Grant Nos.11574394,11774423,and 11822412)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(RUC)(Grant Nos.15XNLQ07,18XNLG14,and 19XNLG17)
文摘We report the detailed physical properties of quaternary compound Ba2BiFeS5 with the key structural ingredient of isolated FeS4 tetrahedra.Magnetization and heat capacity measurements clearly indicate that Ba2BiFeS5 has a paramagnetic to antiferromagnetic transition at about 30 K.The calculated magnetic entropy above ordering temperature is much smaller than theoretical value for high-spin Fe^3+ion with S=5/2,implying the possible short-range antiferromagnetic fluctuation in Ba2BiFeS5.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774421,11774424,11574394,11774423,11822412,and 11874047)the National Key R&D Program of China(Grant Nos.2016YFA0401002,2018YFA0307000,2016YFA0300504,and 2018FYA0305800)the Fundamental Research Funds for the Central Universities,China(Grant No.2042018kf-0030)。
文摘By using angle-resolvea photoemission spectroscopy(ARPES) combined with the first-principies electronic structure calculations,we report the quantized states at the surface of a single crystal 2 H-TaSe_(2).We have observed sub-bands of quantized states at the three-dimensional Brillouin zone center due to a highly dispersive band with light effective mass along k_(z) direction.The quantized sub-bands shift upward towards E_(F) while the bulk band at Γ shifts downward with the decrease of temperature across charge density wave(CDW) formation.The band shifts could be intimately related to the CDW.While neither the two-dimensional Fermi-surface nesting nor purely strong electron-phonon coupling can explain the mechanism of CDW in 2 H-TaSe_(2),our experiment may ignite the interest in understanding the CDW mechanism in this family.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51872328, 12134020, and 12104503)the National Key R&D Program of China (Grant No. 2016YFA0300504)+4 种基金the Fundamental Research Funds for the Central Universities and the Research Funds of Renmin University of China (Grant Nos. 21XNLG18 and 18XNLG24)supported by the China Postdoctoral Science Foundation (Grant No. 2020M680797)supported by the National Key R&D Program of China (Grant No. 2018YFE0202600)the Beijing Natural Science Foundation (Grant No. Z200005)the Fundamental Research Funds for the Central Universities and the Research Funds of Renmin University of China (Grant Nos. 18XNLG14, 19XNLG13, and 19XNLG17)
文摘We performed high-pressure transport studies on the flat-band Kagome compounds,Pd_(3)P_(2)(S_(1−x)Se_(x))_(8)(x=0,0.25),with a diamond anvil cell.For both compounds,the resistivity exhibits an insulating behavior with pressure up to 17GPa.With pressure above 20GPa,a metallic behavior is observed at high temperatures in Pd_(3)P_(2)S_(8),and superconductivity emerges at low temperatures.The onset temperature of superconducting transition T_(C) rises monotonically from 2K to 4.8K and does not saturate with pressure up to 43GPa.For the Se-doped compound Pd_(3)P_(2)(S_(0.75)Se_(0.25))_(8),the T_(C) is about 1.5K higher than that of the undoped one over the whole pressure range,and reaches 6.4K at 43GPa.The upper critical field with field applied along the c axis at typical pressures is about 50%of the Pauli limit,suggesting a 3D superconductivity.The Hall coefficient in the metallic phase is low and exhibits a peaked behavior at about 30 K,which suggests either a multi-band electronic structure or an electron correlation effect in the system.
基金the National Key Research and Development Program of China(Grant Nos.2017YFA0302901,2018YFA0305702,2018YFE0202600,and 2016YFA0300504)the National Natural Science Foundation of China(Grant Nos.12134018,11921004,11822412,and 11774423)+1 种基金the Beijing Natural Science Foundation,China(Grant No.Z200005)the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.XDB33010100)。
文摘We report ^(121)Sb nuclear quadrupole resonance(NQR)measurements on kagome superconductor CsV_(3)Sb_(5) with Tc=2.5 K.^(121)Sb NQR spectra split after a charge density wave(CDW)transition at 94 K,which demonstrates a commensurate CDW state.The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first order phase transition.The CDW order exhibits tri-hexagonal deformation with a lateral shift between the adjacent kagome layers,which is consistent with 2×2×2 superlattice modulation.The superconducting state coexists with CDW order and shows a conventional s-wave behavior in the bulk state.
基金supported by the National Natural Science Foundation of China(U1832202,11888101,11920101005,12141402,and 12274459)the Chinese Academy of Sciences(QYZDB-SSW-SLH043,XDB33020100,and XDB28000000)+4 种基金the Beijing Municipal Science and Technology Commission(Z171100002017018,and Z200005)the National Key R&D Program of China(2018YFE0202600,2022YFA1403100,and 2022YFA1403800)the Fundamental Research Funds for the Central Universities and Research Funds of Renmin University of China(RUC)(18XNLG14,19XNLG13,19XNLG17,and 20XNH062)the Synergic Extreme Condition User Facility,Beijing,ChinaBeijing National Laboratory for Condensed Matter Physics。
基金This work was financially supported by the National Key Research and Development Program of China(No.2022YFA1204004)the National Natural Science Foundation of China(Nos.52071026,52130103,51971026,and 52201288)+3 种基金the ISF-NSFC Joint Research Program(No.51961145305)the Beijing Natural Science Foundation Key Program(No.Z190007)the open research fund of Songshan Lake Materials Laboratory(No.2022SLABFN18)the Fundamental Research Funds for the Central Universities(No.06500140).
文摘Two-dimensional van der Waals(2D vdW)magnets have attracted great attention recently and possess the unprecedented advantages of incorporating high-quality vdW heterostructures and homostructures into spintronic devices,and exploring various physical phenomena or technologies.Among them,Fe_(5)GeTe_(2)(F5GT)has ferromagnetic order close to room temperature,however the magnetic properties near its intrinsic transitions and F5GT-based 2D devices remain mostly unexplored.Here,we systematically demonstrate the peculiar magnetic properties of Fe_(5)GeTe_(2)nanoflakes near its intrinsic transition temperature(Tp)which is far lower than its Curie temperature(TC)of~265 K,and firstly discover anomalous magnetoresistance effect in F5GT homo-junctions by magneto-transport measurements.The strongest anomalous Hall effect occurs around Tp which is located in a temperature range from 130 to 160 K for the F5GT nanoflakes with different thicknesses.Furthermore,negative magnetoresistance(N-MR)and butterfly-shaped magnetoresistance(B-MR)are observed in F5GT homo-junction devices,and they appeared only in an intermediate temperature range from 110 to 160 K,noticeably showing the maxima near the T_(p)rather than the lowest temperature.Our experimental results clearly reveal the significant influence of intrinsic transitions on magnetic properties of F5GT and magnetoresistance effect in F5GT homo-junction devices,which imply a new strategy to achieve highperformance 2D spintronic devices by tuning intrinsic magnetic or structural transitions in 2D vdW magnets.
基金supported by the Minis try of Science and Technology of China (No. 2016YFA0300504)the National Natural Science Foundation of China (Nos. 11574394, 11774423, and 11822412)+3 种基金the Research Funds of Renmin University of China (RUC)(Nos.15XNLF06, 15XNLQ07, and 18XNLG14)the Fundamental Research Funds for the Central Universities (No. 2017RC20)the Research Innovation Fund for College Students of Beijing University of Posts and Telecommunicationsand the Collaborative Research Project of Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology. H. H. was supported by the MEXT Elements Strategy Initiative to Form Core Research Center.
文摘We study the magnetocaloric effect (MCE) in van der Waals (vdW) crystal CrBr3.Bulk CrBr3 exhibits a second-order paramagnetic-ferromagnetic phase transition with TC =33 K.The maximum magnetic entropy change-△SM near TC is about 7.2 J.kg-1.K-1 with the maximum adiabatic temperature change △Tadmax =2.37 K and the relative cooling power RCP =191.5 J.kg-1 at μoH =5 T,all of which are remarkably larger than those in CrI3.These results suggest that the vdW crystal CrBr3 is a promising candidate for the low-dimensional magnetic refrigeration in low temperature region.
基金support by the National Key R&D Program of China (2021YFA1400100)the National Natural Science Foundation of China (11827805 and 12150003)+12 种基金Shanghai Municipal Science and Technology Major Project (2019SHZDZX01)support by the National Key R&D Program of China (2018YFE0202600)Beijing Natural Science Foundation (Z200005)support from JSPS KAKENHI (19H05790, 20H00354, and 21H05233)A3 Foresight by JSPSfinancial support from the National Natural Science Foundation of China (11874115)financial support from the Ministry of Science and Technology (MOST) of China (2018YFE0202700)the National Natural Science Foundation of China (11974422)the Strategic Priority Research Program of Chinese Academy of Sciences (XDB30000000)the Fundamental Research Funds for the Central Universities, Chinathe Research Funds of Renmin University of China (22XNKJ30)supported by the National Natural Science Foundation of China (12104504)the China Postdoctoral Science Foundation (2021 M693479)。
基金the National Natural Science Foundation of China (Grant Nos. 11574394, 11774423, 11822412, and 51608273)the Fundamental Research Funds for the Central Universities (Grant No. 2017RC20)+3 种基金the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (No. 16KJB560008)the Young Researcher Program Nanjing Forestry University of China (No. CX2016023)Key Laboratory of Advanced Building Materials of Anhui Province of China (No. JZCL201603KF)State Key Laboratory of High Performance Civil Engineering Materials of China (No. 2016CEM004).
文摘We have synthesized and investigated physical properties of two new quaternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals, which are isostructural to Tb2NiAl4Ge2 and Er2CoAl4Ge2. The most important structural feature of these materials is the anti-CaF2-type CoAl4T2 slabs. These materials show metallic behavior below 300 K and there is a long-range antiferromagnetic (AFM) transition appearing at 20 and 27 K for GdCoAl4Ge2 and Gd2CoAl4Si2, respectively. Resistivity and heat capacity measurements also confirm these bulk AFM transitions. Further analysis indicates that this long-range antiferromagnetism should result from the magnetic interaction between local moments of Gd^3+ ions.
基金supported by the Ministry of Science and Technology of China(Grant Nos.2016YFA0401000,2016YFA0300600,2018YFE0202600,and 2016YFA0300504)the National Natural Science Foundation of China(Grant Nos.U1832202,11774423,118224121,and 1888101)+4 种基金the Chinese Academy of Sciences(Grant Nos.QYZDB-SSW-SLH043,XDB33020100,and XDB28000000)the Beijing Natural Science Foundation(Grant No.Z200005)the Fundamental Research Funds for the Central Universities and Research Funds of Renmin University of China(Grant Nos.18XNLG14,and 19XNLG17)the Beijing Municipal Science and Technology Commission(Grant No.Z171100002017018)support by the CAS Pioneer“Hundred Talents Program”(type C)。
文摘The CoSi family hosts unconventional topological nodes with nonzero Chern numbers.The nontrivial topology is manifested by conspicuous surface Fermi arcs connecting surface projections of the nodes.Here,using angle-resolved photoemission spectroscopy,we have systematically investigated the(001)surface states of pristine and Ni-doped Co Si.The surface states form saddle-like band structures at/near the time-reversal invariant point near the Fermi level.The Fermi arcs undergo consecutive Lifshitz transitions at the saddle points X,leading to changes of the Fermi arc configuration.As the density of states has a van Hove singularity at the saddle points,exotic many-body physical phenomena may emerge accompanied by the topological transitions of surface Fermi arcs.
基金supported by the National Key R&D Program of China(Grant Nos.2018YFA0704300,2018YFE0202600,and 2017YFA0302903)the National Natural Science Foundation of China(Grant Nos.U1932217,11974246,12004252,12174443,and 11774424)+5 种基金the Natural Science Foundation of Shanghai(Grant No.19ZR1477300)the Science and Technology Commission of Shanghai Municipality(Grant No.19JC1413900)the Shanghai Science and Technology Plan(Grant No.21DZ2260400)the Beijing Natural Science Foundation(Grant No.Z200005)the Fundamental Research Funds for the Central Universities and Research Funds of Renmin University of China(RUC)(Grant Nos.18XNLG14,19XNLG13,19XNLG17,and 22XNKJ40)support from Analytical Instrumentation Center(Grant No.SPSTAIC10112914),SPST,Shanghai Tech University。
文摘The recent discovery of superconductivity up to 32 K in the pressurized MoBreignites the interest in exploring high-Tc superconductors in transition-metal diborides. Inspired by that work, we turn our attention to the 5 d transition-metal diborides.Here we systematically investigate the responses of both structural and physical properties of WBand ReBto external pressure,which possess different types of boron layers. Similar to MoB, the pressure-induced superconductivity was also observed in WBabove 60 GPa with a maximum Tcof 15 K at 100 GPa, while no superconductivity was detected in ReBin this pressure range. Interestingly, the structures at ambient pressure for both WBand ReBpersist to high pressure without structural phase transitions. Theoretical calculations suggest that the ratio of flat boron layers in this class of transition-metal diborides may be crucial for the appearance of high Tc. The combined theoretical and experimental results highlight the effect of the geometry of boron layers on superconductivity and shed light on the exploration of novel high-Tcsuperconductors in borides.