The second magnetization peak(SMP)appears in most superconductors and is crucial for the understanding of vortex physics as well as the application.Although it is well known that the SMP is related to the type and qua...The second magnetization peak(SMP)appears in most superconductors and is crucial for the understanding of vortex physics as well as the application.Although it is well known that the SMP is related to the type and quantity of disorder/defects,the mechanism has not been universally understood.We selected three stoichiometric superconducting RbCa_(2)Fe_(4)As_(4)F_(2)single crystals with identical superconducting critical temperature T_(c)~31 K and similar self-field critical current density J_(c),but with different amounts of disorder/defects,to study the SMP effect.It is found that only the sample S2 with moderate disorder/defects shows significant SMP effect.The evolution of the normalized pinning force density f_(p)demonstrates that the dominant pinning mechanism changes from the weak pinning at low temperatures to strong pinning at high temperatures.The microstructure study for sample S2 reveals some expanded Ca_(2)F_(2)layers and dislocation defects in Rb Fe_(2)As_(2)layers.The normalized magnetic relaxation results indicate that the SMP is strongly associated with the elastic to plastic(E-P)vortex transition.As temperature increases,the SMP gradually evolves into a step-like shape and then becomes a sharp peak near the irreversibility field similar to what is usually observed in low-temperature superconductors.Our findings connect the low field SMP of high-temperature superconductors and the high field peak of lowtemperature superconductors,revealing the possible universal origin related to the E-P phase transition.展开更多
High-pressure structural search was performed on the hydrogen-rich compound LuBeH8at pressures up to 200 GPa.We found an Fm3m structure that exhibits stability and superconductivity above 100 GPa.Our phonon dispersion...High-pressure structural search was performed on the hydrogen-rich compound LuBeH8at pressures up to 200 GPa.We found an Fm3m structure that exhibits stability and superconductivity above 100 GPa.Our phonon dispersion,electronic band structure,and superconductivity analyses in the 100–200 GPa pressure range reveal a strong electron–phonon coupling in Lu Be H8,while the superconducting critical temperature Tcshows a decreasing trend as the pressure increases,with T_(c)=255 K at 200 GPa and maximal T_(c)=355 K at 100 GPa.This study demonstrated the room-temperature superconductivity in Fm3m thus enriching the family of ternary hydrides.These findings provide valuable guidance for identifying new high-temperature superconducting hydrides.展开更多
Research of vortex properties in type-Ⅱsuperconductors is of great importance for potential applications and fundamental physics.Here,we present a comprehensive study of the critical current density Jc,vortex pinning...Research of vortex properties in type-Ⅱsuperconductors is of great importance for potential applications and fundamental physics.Here,we present a comprehensive study of the critical current density Jc,vortex pinning,and phase diagram of Na Cl-type In Te_(1-x)Se_(x)(x=0,0.1,0.2)superconductors synthesized by high-pressure technique.Our studies reveal that the values of Jc calculated by the Bean model exceed 10^(4)A/cm^(2)in the In Te_(1-x)Se_(x)system,signifying good potential for applications.The magnetic hysteresis loops(MHLs)show an asymmetric characteristic at various degrees,which is associated with the surface barrier.Intriguingly,a rare phenomenon in which the second magnetization peak in the MHLs occurs only in the field-descending branch is detected in In Te_(0.9)Se_(0.1).Such an anomalous behavior has not been observed before and can be described by considering the respective roles of the surface barrier and bulk pinning in the field-ascending and field-descending branches.By analyzing the pinning force density versus reduced field,the pinning mechanisms are studied in detail in the framework of the Dew-Hughes model.Finally,combining the results of resistivity and magnetization measurements,the vortex phase diagrams are constructed and discussed.展开更多
Unconventional superconductivity,in particular,in noncentrosymmetric systems,has been a long-sought topic in condensed matter physics.Recently,Re-based superconductors have attracted great attention owing to the poten...Unconventional superconductivity,in particular,in noncentrosymmetric systems,has been a long-sought topic in condensed matter physics.Recently,Re-based superconductors have attracted great attention owing to the potential time-reversal symmetry breaking in their superconducting states.We report the superconducting properties of noncentrosymmetric compounds Ta_(x)Re_(1-x) with 0.1 ≤x≤0.25,and find that the superconducting transition temperature reaches a maximum of ~8 K at the optimal level x=0.15.Nevertheless,muon-spin rotation and relaxation measurements reveal no time-reversal symmetry breaking existing in its superconducting state,which is in sharp contrast to both centrosymmetric Re metal and many other noncentrosymmetric Re-based superconductors.展开更多
Due to non-saturating magnetoresistance(MR)and the special compensation mechanism,the Weyl semimetal Ta As single crystal has attracted considerable attention in condensed matter physics.Herein,we use maximum entropy ...Due to non-saturating magnetoresistance(MR)and the special compensation mechanism,the Weyl semimetal Ta As single crystal has attracted considerable attention in condensed matter physics.Herein,we use maximum entropy mobility spectrum analysis(MEMSA)to extract charge carrier information by fitting the experimentally measured longitudinal and transverse electric transport curves of Ta As.The carrier types and the number of bands are obtained without any hypothesis.Study of the temperature dependence shows details of carrier property evolution.Our quantitative results explain the nonsaturated magnetoresistance and Hall sign change phenomena of TaAs.展开更多
基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB25000000)the National Key R&D Program of China(Grant No.2018YFA0704300)+1 种基金the National Natural Science Foundation of China(Grant Nos.12204265 and 12204487)the Fundamental Research Funds for the Central Universities。
文摘The second magnetization peak(SMP)appears in most superconductors and is crucial for the understanding of vortex physics as well as the application.Although it is well known that the SMP is related to the type and quantity of disorder/defects,the mechanism has not been universally understood.We selected three stoichiometric superconducting RbCa_(2)Fe_(4)As_(4)F_(2)single crystals with identical superconducting critical temperature T_(c)~31 K and similar self-field critical current density J_(c),but with different amounts of disorder/defects,to study the SMP effect.It is found that only the sample S2 with moderate disorder/defects shows significant SMP effect.The evolution of the normalized pinning force density f_(p)demonstrates that the dominant pinning mechanism changes from the weak pinning at low temperatures to strong pinning at high temperatures.The microstructure study for sample S2 reveals some expanded Ca_(2)F_(2)layers and dislocation defects in Rb Fe_(2)As_(2)layers.The normalized magnetic relaxation results indicate that the SMP is strongly associated with the elastic to plastic(E-P)vortex transition.As temperature increases,the SMP gradually evolves into a step-like shape and then becomes a sharp peak near the irreversibility field similar to what is usually observed in low-temperature superconductors.Our findings connect the low field SMP of high-temperature superconductors and the high field peak of lowtemperature superconductors,revealing the possible universal origin related to the E-P phase transition.
基金supported by the National Key R&D Program of China(Grant No.2018YFA0704300)the National Natural Science Foundation of China(Grant No.U1932217)the StartUp Fund of Nanjing University of Posts and Telecommunications(Grant Nos.NY219087 and NY220038)。
文摘High-pressure structural search was performed on the hydrogen-rich compound LuBeH8at pressures up to 200 GPa.We found an Fm3m structure that exhibits stability and superconductivity above 100 GPa.Our phonon dispersion,electronic band structure,and superconductivity analyses in the 100–200 GPa pressure range reveal a strong electron–phonon coupling in Lu Be H8,while the superconducting critical temperature Tcshows a decreasing trend as the pressure increases,with T_(c)=255 K at 200 GPa and maximal T_(c)=355 K at 100 GPa.This study demonstrated the room-temperature superconductivity in Fm3m thus enriching the family of ternary hydrides.These findings provide valuable guidance for identifying new high-temperature superconducting hydrides.
基金the National Natural Science Foundation of China(Grant Nos.12204265 and 12204487)the Natural Science Foundation of Shandong Province(Grant Nos.ZR2022QA040,2022KJ183,and 2019KJJ020)+1 种基金the National Key R&D Program of China(Grant No.2018YFA0704300)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB25000000)。
文摘Research of vortex properties in type-Ⅱsuperconductors is of great importance for potential applications and fundamental physics.Here,we present a comprehensive study of the critical current density Jc,vortex pinning,and phase diagram of Na Cl-type In Te_(1-x)Se_(x)(x=0,0.1,0.2)superconductors synthesized by high-pressure technique.Our studies reveal that the values of Jc calculated by the Bean model exceed 10^(4)A/cm^(2)in the In Te_(1-x)Se_(x)system,signifying good potential for applications.The magnetic hysteresis loops(MHLs)show an asymmetric characteristic at various degrees,which is associated with the surface barrier.Intriguingly,a rare phenomenon in which the second magnetization peak in the MHLs occurs only in the field-descending branch is detected in In Te_(0.9)Se_(0.1).Such an anomalous behavior has not been observed before and can be described by considering the respective roles of the surface barrier and bulk pinning in the field-ascending and field-descending branches.By analyzing the pinning force density versus reduced field,the pinning mechanisms are studied in detail in the framework of the Dew-Hughes model.Finally,combining the results of resistivity and magnetization measurements,the vortex phase diagrams are constructed and discussed.
基金Supported by the National Key R&D Program of China(Grant No.2018YFA0704300)the National Natural Science Foundation of China(Grant Nos.U1732162,11974061,11704047,U1832147 and 11674054)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB25000000)。
文摘Unconventional superconductivity,in particular,in noncentrosymmetric systems,has been a long-sought topic in condensed matter physics.Recently,Re-based superconductors have attracted great attention owing to the potential time-reversal symmetry breaking in their superconducting states.We report the superconducting properties of noncentrosymmetric compounds Ta_(x)Re_(1-x) with 0.1 ≤x≤0.25,and find that the superconducting transition temperature reaches a maximum of ~8 K at the optimal level x=0.15.Nevertheless,muon-spin rotation and relaxation measurements reveal no time-reversal symmetry breaking existing in its superconducting state,which is in sharp contrast to both centrosymmetric Re metal and many other noncentrosymmetric Re-based superconductors.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674054,U1932217,and 11704067)。
文摘Due to non-saturating magnetoresistance(MR)and the special compensation mechanism,the Weyl semimetal Ta As single crystal has attracted considerable attention in condensed matter physics.Herein,we use maximum entropy mobility spectrum analysis(MEMSA)to extract charge carrier information by fitting the experimentally measured longitudinal and transverse electric transport curves of Ta As.The carrier types and the number of bands are obtained without any hypothesis.Study of the temperature dependence shows details of carrier property evolution.Our quantitative results explain the nonsaturated magnetoresistance and Hall sign change phenomena of TaAs.
