Chiral magnets have attracted considerable attention due to their intricate magnetic properties,among which B20compounds constitute a quintessential class that has gained significant focus,particularly in the study of...Chiral magnets have attracted considerable attention due to their intricate magnetic properties,among which B20compounds constitute a quintessential class that has gained significant focus,particularly in the study of skyrmions.MnGe,as a member of the B20 family,exhibits a more complex magnetic structure compared with other materials with similar crystal structures.In this work,we successfully synthesized high-quality MnGe thin films and characterized their magnetoresistance,M-H curves,magneto-Seebeck effect,and magnetic force microscopy(MFM)images,all of which demonstrate pronounced magnetic anisotropy.Notably,the Seebeck coefficient exhibits a plateau at low magnetic fields when the magnetic field is applied in the film plane,indicating a field region in which the magnetic structure remains stable.MFM imaging further reveals magnetic transitions within the MnGe films when the magnetic field is oriented along the film plane.These findings are crucial for advancing our understanding of the magnetic ground state of MnGe and the evolution of its magnetic structure under an applied external magnetic field.展开更多
The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped i...The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe_(1-x)Co_(x))_(2)As_(2),suggesting a strong interplay between nematicity and superconductivity.Since the long-range spin order is absent in FeSe superconductor,whether a similar strain effect could be also observed or not is an interesting question.Here,by utilizing a flexible film as substrate,we successfully achieve a wide-range-strain tuning of FeSe thin flake,in which both the tensile and compressive strain could reach up to~0.7%,and systematically study the strain effect on both superconducting and nematic transition(T_(c)and Ts)in the FeSe thin flake.Our results reveal a predominant A1g-type strain effect on T_(c).Meanwhile,Ts exhibits a monotonic anti-correlation with T_(c)and the maximum T_(c)reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain.Finally,in comparison with the results in the underdoped Ba(Fe_(1-x)Co_(x))_(2)As_(2),the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity.In addition,our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.展开更多
Recently,competing electronic instabilities,including superconductivity and density-wave-like order,have been discovered in vanadium-based kagome metals AV_(3)Sb_(5)(A=K,Rb,Cs)with a nontrivial band topology.This find...Recently,competing electronic instabilities,including superconductivity and density-wave-like order,have been discovered in vanadium-based kagome metals AV_(3)Sb_(5)(A=K,Rb,Cs)with a nontrivial band topology.This finding stimulates considerable interest to study the interplay of these competing electronic orders and possible exotic excitations in the superconducting state.Here,we performed51V and133Cs nuclear magnetic resonance(NMR)measurements on a CsV_(3)Sb_(5)single crystal to clarify the nature of density-wave-like transition in these kagome superconductors.A first-order structural transition is unambiguously revealed below T_(s)~94 K by observing the sudden splitting of Knight shift in^(51)V NMR spectrum.Moreover,combined with^(133)Cs NMR spectrum,the present result confirms a three-dimensional structural modulation.By further analyzing the anisotropy of Knight shift and 1/T_(1)T at^(51)V nuclei,we proposed that the orbital order is the primary electronic order induced by the firstorder structural transition,which is supported by further analysis on electric field gradient at^(51)V nuclei.In addition,the evidence for possible orbital fluctuations is also revealed above T_(s).The present work sheds light on a rich orbital physics in kagome superconductors AV_(3)Sb_(5).展开更多
Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit （ZT） in three-dimensional Dirac semimetal Cd3A 5 2 crystal. It is fo...Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit （ZT） in three-dimensional Dirac semimetal Cd3A 5 2 crystal. It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 T. The huge enhancement of ZT by magnetic field arises from the linear Dirac band with large Fermi velocity and the large electric thermal conductivity in CdsA 5 2. Our work paves a new way to greatly enhance the thermoelectric performance in the quantum topological materials.展开更多
The origin of the ～40 and ～30 K superconducting phases in the metal-intercalated FeSe superconductors is still unclear. We report the synthesis of K_(0.3)(NH_3)_y(FeSe_(1-x)Te_x)_2 and K_(0.6)(NH_3)_y(FeSe_(1-x)Te_x...The origin of the ～40 and ～30 K superconducting phases in the metal-intercalated FeSe superconductors is still unclear. We report the synthesis of K_(0.3)(NH_3)_y(FeSe_(1-x)Te_x)_2 and K_(0.6)(NH_3)_y(FeSe_(1-x)Te_x)_2 with x=0-0.6 by using the liquid ammonia method at room temperature. The superconducting transition temperature Tcof the former remains about 43 K for all the nominal Te content less than 0.3, while that of the latter is about 30 K and obviously decreases with Te doping. Superconductivity disappears for x ≥0.4 in both systems. Except for the different chemical pressure induced by substitution of Te for Se in both systems, we also observed distinct external pressure effect on superconductivity for both systems, with much more efficiency of suppressing Tcby external pressure in the former system. These dramatic differences of both chemical and external pressure effects on Tc between the ～30 and ～40 K superconducting phases revealed that the existence of the two superconducting phases can be ascribed to the moderate and negligible coupling between FeSe layers, respectively.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12488201,12274390,12304035,and 51627901)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000)+3 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302802)the National Key R&D Program of the MOST of China(Grant No.2022YFA1602600)the Basic Research Program of the Chinese Academy of Sciences Based on Major Scientific Infrastructures(Grant No.JZHKYPT-2021-08)the National Key R&D Program of China(Grant No.2023YFA1607701)。
文摘Chiral magnets have attracted considerable attention due to their intricate magnetic properties,among which B20compounds constitute a quintessential class that has gained significant focus,particularly in the study of skyrmions.MnGe,as a member of the B20 family,exhibits a more complex magnetic structure compared with other materials with similar crystal structures.In this work,we successfully synthesized high-quality MnGe thin films and characterized their magnetoresistance,M-H curves,magneto-Seebeck effect,and magnetic force microscopy(MFM)images,all of which demonstrate pronounced magnetic anisotropy.Notably,the Seebeck coefficient exhibits a plateau at low magnetic fields when the magnetic field is applied in the film plane,indicating a field region in which the magnetic structure remains stable.MFM imaging further reveals magnetic transitions within the MnGe films when the magnetic field is oriented along the film plane.These findings are crucial for advancing our understanding of the magnetic ground state of MnGe and the evolution of its magnetic structure under an applied external magnetic field.
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFA0303000 and 2016YFA0300201)the National Natural Science Foundation of China(Grant No.11888101)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000).
文摘The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe_(1-x)Co_(x))_(2)As_(2),suggesting a strong interplay between nematicity and superconductivity.Since the long-range spin order is absent in FeSe superconductor,whether a similar strain effect could be also observed or not is an interesting question.Here,by utilizing a flexible film as substrate,we successfully achieve a wide-range-strain tuning of FeSe thin flake,in which both the tensile and compressive strain could reach up to~0.7%,and systematically study the strain effect on both superconducting and nematic transition(T_(c)and Ts)in the FeSe thin flake.Our results reveal a predominant A1g-type strain effect on T_(c).Meanwhile,Ts exhibits a monotonic anti-correlation with T_(c)and the maximum T_(c)reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain.Finally,in comparison with the results in the underdoped Ba(Fe_(1-x)Co_(x))_(2)As_(2),the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity.In addition,our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.
基金supported by the National Key R&D Program of China(Grant Nos.2017YFA0303000,and 2016YFA0300201)the National Natural Science Foundation of China(Grant Nos.11888101,and 12034004)+2 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB25000000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000)the Collaborative Innovation Program of Hefei Science Center,CAS(Grant No.2019HSCCIP007)。
文摘Recently,competing electronic instabilities,including superconductivity and density-wave-like order,have been discovered in vanadium-based kagome metals AV_(3)Sb_(5)(A=K,Rb,Cs)with a nontrivial band topology.This finding stimulates considerable interest to study the interplay of these competing electronic orders and possible exotic excitations in the superconducting state.Here,we performed51V and133Cs nuclear magnetic resonance(NMR)measurements on a CsV_(3)Sb_(5)single crystal to clarify the nature of density-wave-like transition in these kagome superconductors.A first-order structural transition is unambiguously revealed below T_(s)~94 K by observing the sudden splitting of Knight shift in^(51)V NMR spectrum.Moreover,combined with^(133)Cs NMR spectrum,the present result confirms a three-dimensional structural modulation.By further analyzing the anisotropy of Knight shift and 1/T_(1)T at^(51)V nuclei,we proposed that the orbital order is the primary electronic order induced by the firstorder structural transition,which is supported by further analysis on electric field gradient at^(51)V nuclei.In addition,the evidence for possible orbital fluctuations is also revealed above T_(s).The present work sheds light on a rich orbital physics in kagome superconductors AV_(3)Sb_(5).
基金supported by the National Key R&D Program of the Ministry of Science and Technology China(2017YFA0303001,2016YFA0300201 and 2017YFA0204904)the National Natural Science Foundation of China(11534010,11774325 and21603210)+4 种基金the Key Research Program of Frontier Sciences CAS(QYZDY-SSW-SLH021)Hefei Science Center CAS(2016HSCIU001)the Fundamental Research Funds for the Central UniversitiesSupercomputing Center at USTC for providing the computing resourcespartially performed on the Superconducting Magnet and PPMS-16T Facilities,High Magnetic Field Laboratory of CAS
文摘Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit （ZT） in three-dimensional Dirac semimetal Cd3A 5 2 crystal. It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 T. The huge enhancement of ZT by magnetic field arises from the linear Dirac band with large Fermi velocity and the large electric thermal conductivity in CdsA 5 2. Our work paves a new way to greatly enhance the thermoelectric performance in the quantum topological materials.
基金supported by the National Natural Science Foundation of China(Grants Nos.11374252,11604278,11534010,and 91422303)the National Key R&D Program of the MOST of China(Grant No.2017YFA0303001)+1 种基金the Hefei Science Center Chinese Academy Sciences(Grant No.2016HSC-IU001)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB04040100)
文摘The origin of the ～40 and ～30 K superconducting phases in the metal-intercalated FeSe superconductors is still unclear. We report the synthesis of K_(0.3)(NH_3)_y(FeSe_(1-x)Te_x)_2 and K_(0.6)(NH_3)_y(FeSe_(1-x)Te_x)_2 with x=0-0.6 by using the liquid ammonia method at room temperature. The superconducting transition temperature Tcof the former remains about 43 K for all the nominal Te content less than 0.3, while that of the latter is about 30 K and obviously decreases with Te doping. Superconductivity disappears for x ≥0.4 in both systems. Except for the different chemical pressure induced by substitution of Te for Se in both systems, we also observed distinct external pressure effect on superconductivity for both systems, with much more efficiency of suppressing Tcby external pressure in the former system. These dramatic differences of both chemical and external pressure effects on Tc between the ～30 and ～40 K superconducting phases revealed that the existence of the two superconducting phases can be ascribed to the moderate and negligible coupling between FeSe layers, respectively.
