We report a hydrothermal route to remove interstitial excess Fe in non-superconducting iron chalcogenide Fe_(1+δ)Se_(1-x)Te_(x) single crystals.The extra-Fe-free(δ~0)FeSe_(0.2)Te_(0.8) single crystal thus obtained s...We report a hydrothermal route to remove interstitial excess Fe in non-superconducting iron chalcogenide Fe_(1+δ)Se_(1-x)Te_(x) single crystals.The extra-Fe-free(δ~0)FeSe_(0.2)Te_(0.8) single crystal thus obtained shows bulk superconductivity at T_c~13.8 K,which is about 2 K higher than the FeSe_(0.2)Te_(0.8) sample obtained by usual postannealing process.The upper critical fieldμ_0H_(c2) is estimated to be~42.5 T,similar to the annealed FeSe_(0.2)Te_(0.8).It is surprising to find that the hydrothermal FeSe_(0.2)Te_(0.8)exhibits a remarkably small isothermal magnetization hysteresis loop at T=3 K.This yields an extremely low critical current density J_(c)~1.1×10^(2)A·cm^(-2)(over 100times smaller than the annealed FeSe_(0.2)Te_(0.8)) and indicates more free vortices in the hydrothermal FeSe_(0.2)Te_(0.8).展开更多
We report the observation for the pz electron band and the band inversion in Fe1+yTexSe1-xwith angleresolved photoemission spectroscopy. Furthermore, we found that excess Fe(y>0) inhibits the topological band inver...We report the observation for the pz electron band and the band inversion in Fe1+yTexSe1-xwith angleresolved photoemission spectroscopy. Furthermore, we found that excess Fe(y>0) inhibits the topological band inversion in Fe1+yTexSe1-x,which explains the absence of Majorana zero modes in previous reports for Fe1+yTexSe1-xwith excess Fe. Based on our analysis of different amounts of Te doping and excess Fe, we propose a delicate topological phase in this material. Thanks to this delicate phase, one may be able to tune the topological transition via applying lattice strain or carrier doping.展开更多
The intercalated iron selenide(Li,Fe)OHFeSe has a strongly layered structure analogous to the quasi-twodimensional(2D)bismuth cuprate superconductors,and exhibits both high-temperature(Tc)and topological superconducti...The intercalated iron selenide(Li,Fe)OHFeSe has a strongly layered structure analogous to the quasi-twodimensional(2D)bismuth cuprate superconductors,and exhibits both high-temperature(Tc)and topological superconductivity.However,the issue of its superconductivity dimensionality has not yet been fully investigated so far.Here we report that the quasi-2D superconductivity features,including the high anisotropyγ=151 and the associated quasi-2D vortices,are also revealed for(Li,Fe)OHFeSe,based on systematic experiments of the electrical transport and magnetization and model fittings.Thus,we establish a new vortex phase diagram for(Li,Fe)OHFeSe,which delineates an emergent quasi-2D vortex-liquid state,and a subsequent vortex-solid dimensional crossover from a pancake-like to a three-dimensional state with decreasing temperature and magnetic field.Furthermore,we find that all the quasi-2D characteristics revealed here for the high-Tciron selenide superconductor are very similar to those reported for high-Tcbismuth cuprate superconductors.展开更多
The electronic and superconducting properties of Fe_(1-δ)Se single-crystal flakes grown hydrothermally are studied by the transport measurements under zero and high magnetic fields up to 38.5 T.The results contrast s...The electronic and superconducting properties of Fe_(1-δ)Se single-crystal flakes grown hydrothermally are studied by the transport measurements under zero and high magnetic fields up to 38.5 T.The results contrast sharply with those previously reported for nematically ordered Fe Se by chemical-vapor-transport(CVT)growth.No signature of the electronic nematicity,but an evident metal-to-nonmetal crossover with increasing temperature,is detected in the normal state of the present hydrothermal samples.Interestingly,a higher superconducting critical temperature T_c of 13.2 K is observed compared to a suppressed T_c of 9 K in the presence of the nematicity in the CVT Fe Se.Moreover,the upper critical field in the zero-temperature limit is found to be isotropic with respect to the field direction and to reach a higher value of-42 T,which breaks the Pauli limit by a factor of 1.8.展开更多
We systematically measure the superconducting(SC)and mixed state properties of high-quality CsV_3 Sb_5 single crystals with T_c-3.5 K.We find that the upper critical field H_(c2)(T)exhibits a large anisotropic ratio o...We systematically measure the superconducting(SC)and mixed state properties of high-quality CsV_3 Sb_5 single crystals with T_c-3.5 K.We find that the upper critical field H_(c2)(T)exhibits a large anisotropic ratio of H_(c2)^(ab)/H_(c2)^c^9 at zero temperature and fitting its temperature dependence requires a minimum two-band effective model.Moreover,the ratio of the lower critical field,H_(c1)^(ab)/H_(c1)^c,is also found to be larger than 1,which indicates that the in-plane energy dispersion is strongly renormalized near Fermi energy.Both H_(c1)(T)and SC diamagnetic signal are found to change little initially below T_c-3.5 K and then to increase abruptly upon cooling to a characteristic temperature of-2.8 K.Furthermore,we identify a two-fold anisotropy of in-plane angular-dependent magnetoresistance in the mixed state.Interestingly,we find that,below the same characteristic T-2.8 K,the orientation of this two-fold anisotropy displays a peculiar twist by an angle of 60°characteristic of the Kagome geometry.Our results suggest an intriguing superconducting state emerging in the complex environment of Kagome lattice,which,at least,is partially driven by electron-electron correlation.展开更多
The angular-dependent magnetoresistance(AMR)of the ab plane is measured on the single crystals of ironchalcogenide FeSe_(1-x)S_(x)(x=0,0.07,0.13 and 1)and FeSe_(1-y)Te_(y)(y=0.06,0.61 and 1)at various temperatures und...The angular-dependent magnetoresistance(AMR)of the ab plane is measured on the single crystals of ironchalcogenide FeSe_(1-x)S_(x)(x=0,0.07,0.13 and 1)and FeSe_(1-y)Te_(y)(y=0.06,0.61 and 1)at various temperatures under fields up to 9 T.A pronounced twofold-anisotropic carrier-scattering effect is identified by AMR,and attributed to a magnetic-field-induced spin nematicity that emerges from the tetragonal normal-state regime below a characteristic temperature Tsn.This magnetically polarized spin nematicity is found to be ubiquitous in the isoelectronic FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)systems,no matter whether the sample shows an electronic nematic order at T_(s)≤T_(sn),or an antiferromagnetic order at TN<T_(sn),or neither order.Importantly,we find that the induced spin nematicity shows a very different response to sulfur substitution from the spontaneous electronic nematicity:The spin-nematic T_(sn)is not suppressed but even enhanced by the substitution,whereas the electronicnematic T_(s)is rapidly suppressed,in the FeSe_(1-x)S_(x)system.Furthermore,we find that the superconductivity is significantly suppressed with the enhancement of the induced spin nematicity in both FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)samples.展开更多
The vanadium-based kagome superconductor CsV_(3)Sb_(5) has attracted tremendous attention due to its unexcepted anomalous Hall effect(AHE),charge density waves(CDWs),nematicity,and a pseudogap pair density wave(PDW)co...The vanadium-based kagome superconductor CsV_(3)Sb_(5) has attracted tremendous attention due to its unexcepted anomalous Hall effect(AHE),charge density waves(CDWs),nematicity,and a pseudogap pair density wave(PDW)coexisting with unconventional strong-coupling superconductivity.The origins of CDWs,unconventional superconductivity,and their correlation with different electronic states in this kagome system are of great significance,but so far,are still under debate.Chemical doping in the kagome layer provides one of the most direct ways to reveal the intrinsic physics,but remains unexplored.Here,we report,for the first time,the synthesis of Ti-substituted CsV_(3)Sb_(5) single crystals and its rich phase diagram mapping the evolution of intertwining electronic states.The Ti atoms directly substitute for V in the kagome layers.CsV_(3-x)Ti_(x)Sb_(5) shows two distinct superconductivity phases upon substitution.The Ti slightly-substituted phase displays an unconventional V-shaped superconductivity gap,coexisting with weakening CDW,PDW,AHE,and nematicity.The Ti highly-substituted phase has a U-shaped superconductivity gap concomitant with a short-range rotation symmetry breaking CDW,while long-range CDW,twofold symmetry of in-plane resistivity,AHE,and PDW are absent.Furthermore,we also demonstrate the chemical substitution of V atoms with other elements such as Cr and Nb,showing a different modulation on the superconductivity phases and CDWs.These findings open up a way to synthesise a new family of doped CsV_(3)Sb_(5) materials,and further represent a new platform for tuning the different correlated electronic states and superconducting pairing in kagome superconductors.展开更多
基金the National Natural Science Foundation of China(Grant Nos.12061131005,11974019,11834016,and 11888101)the National Key Research and Development Program of China(Grant Nos.2022YFA1403900)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB33010200 and XDB25000000)the Chinese Academy of Sciences through the Youth Innovation Promotion Association(Grant No.2022YSBR-048)。
文摘We report a hydrothermal route to remove interstitial excess Fe in non-superconducting iron chalcogenide Fe_(1+δ)Se_(1-x)Te_(x) single crystals.The extra-Fe-free(δ~0)FeSe_(0.2)Te_(0.8) single crystal thus obtained shows bulk superconductivity at T_c~13.8 K,which is about 2 K higher than the FeSe_(0.2)Te_(0.8) sample obtained by usual postannealing process.The upper critical fieldμ_0H_(c2) is estimated to be~42.5 T,similar to the annealed FeSe_(0.2)Te_(0.8).It is surprising to find that the hydrothermal FeSe_(0.2)Te_(0.8)exhibits a remarkably small isothermal magnetization hysteresis loop at T=3 K.This yields an extremely low critical current density J_(c)~1.1×10^(2)A·cm^(-2)(over 100times smaller than the annealed FeSe_(0.2)Te_(0.8)) and indicates more free vortices in the hydrothermal FeSe_(0.2)Te_(0.8).
基金supported by the National Natural Science Foundation of China(Grant Nos.11888101 and U1832202)the Chinese Academy of Sciences(Grant Nos.QYZDB-SSW-SLH043,XDB28000000,and XDB33000000)+3 种基金the K.C.Wong Education Foundation(Grant No.GJTD-2018-01)the Informatization Plan of Chinese Academy of Sciences(Grant No.CAS-WX2021SF-0102)supported by the Synergetic Extreme Condition User Facility(SECUF)supported by US DOE(Grant Nos.DESC0010526 and DE-SC0012704)。
文摘We report the observation for the pz electron band and the band inversion in Fe1+yTexSe1-xwith angleresolved photoemission spectroscopy. Furthermore, we found that excess Fe(y>0) inhibits the topological band inversion in Fe1+yTexSe1-x,which explains the absence of Majorana zero modes in previous reports for Fe1+yTexSe1-xwith excess Fe. Based on our analysis of different amounts of Te doping and excess Fe, we propose a delicate topological phase in this material. Thanks to this delicate phase, one may be able to tune the topological transition via applying lattice strain or carrier doping.
基金supported by the National Natural Science Foundation of China(Grant Nos.12061131005,11834016,and 11888101)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB33010200 and XDB25000000)。
文摘The intercalated iron selenide(Li,Fe)OHFeSe has a strongly layered structure analogous to the quasi-twodimensional(2D)bismuth cuprate superconductors,and exhibits both high-temperature(Tc)and topological superconductivity.However,the issue of its superconductivity dimensionality has not yet been fully investigated so far.Here we report that the quasi-2D superconductivity features,including the high anisotropyγ=151 and the associated quasi-2D vortices,are also revealed for(Li,Fe)OHFeSe,based on systematic experiments of the electrical transport and magnetization and model fittings.Thus,we establish a new vortex phase diagram for(Li,Fe)OHFeSe,which delineates an emergent quasi-2D vortex-liquid state,and a subsequent vortex-solid dimensional crossover from a pancake-like to a three-dimensional state with decreasing temperature and magnetic field.Furthermore,we find that all the quasi-2D characteristics revealed here for the high-Tciron selenide superconductor are very similar to those reported for high-Tcbismuth cuprate superconductors.
基金Supported by the National Key Research and Development Program of China (Grant Nos.2016YFA0300300 and 2017YFA0303003)the National Natural Science Foundation of China (Grant Nos.12061131005,11834016 and 11888101)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No.XDB25000000)the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant Nos.QYZDY-SSW-SLH001)。
文摘The electronic and superconducting properties of Fe_(1-δ)Se single-crystal flakes grown hydrothermally are studied by the transport measurements under zero and high magnetic fields up to 38.5 T.The results contrast sharply with those previously reported for nematically ordered Fe Se by chemical-vapor-transport(CVT)growth.No signature of the electronic nematicity,but an evident metal-to-nonmetal crossover with increasing temperature,is detected in the normal state of the present hydrothermal samples.Interestingly,a higher superconducting critical temperature T_c of 13.2 K is observed compared to a suppressed T_c of 9 K in the presence of the nematicity in the CVT Fe Se.Moreover,the upper critical field in the zero-temperature limit is found to be isotropic with respect to the field direction and to reach a higher value of-42 T,which breaks the Pauli limit by a factor of 1.8.
基金Supported by the National Natural Science Foundation of China (Grant Nos.11834016,11888101,12061131005,51771224 and61888102)the National Key Research and Development Projects of China (Grant Nos.2017YFA0303003 and 2018YFA0305800)the Key Research Program and Strategic Priority Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant Nos.QYZDY-SSW-SLH001,XDB33010200 and XDB25000000)。
文摘We systematically measure the superconducting(SC)and mixed state properties of high-quality CsV_3 Sb_5 single crystals with T_c-3.5 K.We find that the upper critical field H_(c2)(T)exhibits a large anisotropic ratio of H_(c2)^(ab)/H_(c2)^c^9 at zero temperature and fitting its temperature dependence requires a minimum two-band effective model.Moreover,the ratio of the lower critical field,H_(c1)^(ab)/H_(c1)^c,is also found to be larger than 1,which indicates that the in-plane energy dispersion is strongly renormalized near Fermi energy.Both H_(c1)(T)and SC diamagnetic signal are found to change little initially below T_c-3.5 K and then to increase abruptly upon cooling to a characteristic temperature of-2.8 K.Furthermore,we identify a two-fold anisotropy of in-plane angular-dependent magnetoresistance in the mixed state.Interestingly,we find that,below the same characteristic T-2.8 K,the orientation of this two-fold anisotropy displays a peculiar twist by an angle of 60°characteristic of the Kagome geometry.Our results suggest an intriguing superconducting state emerging in the complex environment of Kagome lattice,which,at least,is partially driven by electron-electron correlation.
基金the National Key Research and Development Program of China(Grant Nos.2016YFA0300300 and 2017YFA0303003)the National Natural Science Foundation of China(Grant Nos.12061131005,11834016,and 11888101)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB25000000)the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant Nos.QYZDY-SSW-SLH001)。
文摘The angular-dependent magnetoresistance(AMR)of the ab plane is measured on the single crystals of ironchalcogenide FeSe_(1-x)S_(x)(x=0,0.07,0.13 and 1)and FeSe_(1-y)Te_(y)(y=0.06,0.61 and 1)at various temperatures under fields up to 9 T.A pronounced twofold-anisotropic carrier-scattering effect is identified by AMR,and attributed to a magnetic-field-induced spin nematicity that emerges from the tetragonal normal-state regime below a characteristic temperature Tsn.This magnetically polarized spin nematicity is found to be ubiquitous in the isoelectronic FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)systems,no matter whether the sample shows an electronic nematic order at T_(s)≤T_(sn),or an antiferromagnetic order at TN<T_(sn),or neither order.Importantly,we find that the induced spin nematicity shows a very different response to sulfur substitution from the spontaneous electronic nematicity:The spin-nematic T_(sn)is not suppressed but even enhanced by the substitution,whereas the electronicnematic T_(s)is rapidly suppressed,in the FeSe_(1-x)S_(x)system.Furthermore,we find that the superconductivity is significantly suppressed with the enhancement of the induced spin nematicity in both FeSe_(1-x)S_(x)and FeSe_(1-y)Te_(y)samples.
基金supported by grants from the National Natural Science Foundation of China(61888102,52022105,51771224,11888101,12061131005,and 11834016)the National Key Research and Development Projects of China(2018YFA0305800 and 2019YFA0308500)+6 种基金the Chinese Academy of Sciences(XDB33030100,XDB28010200,and XDB30010000)the Key Research Program of Chinese Academy of Sciences(ZDBS-SSWWHC001)the CAS Project for Young Scientists in Basic Research(YSBR-003)the Beijing Outstanding Young Scientist Program(BJJWZYJH01201914430039)supported by the US DOE,Basic Energy Sciences Grant(DE-FG02-99ER45747)the financial support by the European Research Council(ERC Consolidator Grant,No.815869)the Israel Science Foundation(ISF No.1251/19)。
文摘The vanadium-based kagome superconductor CsV_(3)Sb_(5) has attracted tremendous attention due to its unexcepted anomalous Hall effect(AHE),charge density waves(CDWs),nematicity,and a pseudogap pair density wave(PDW)coexisting with unconventional strong-coupling superconductivity.The origins of CDWs,unconventional superconductivity,and their correlation with different electronic states in this kagome system are of great significance,but so far,are still under debate.Chemical doping in the kagome layer provides one of the most direct ways to reveal the intrinsic physics,but remains unexplored.Here,we report,for the first time,the synthesis of Ti-substituted CsV_(3)Sb_(5) single crystals and its rich phase diagram mapping the evolution of intertwining electronic states.The Ti atoms directly substitute for V in the kagome layers.CsV_(3-x)Ti_(x)Sb_(5) shows two distinct superconductivity phases upon substitution.The Ti slightly-substituted phase displays an unconventional V-shaped superconductivity gap,coexisting with weakening CDW,PDW,AHE,and nematicity.The Ti highly-substituted phase has a U-shaped superconductivity gap concomitant with a short-range rotation symmetry breaking CDW,while long-range CDW,twofold symmetry of in-plane resistivity,AHE,and PDW are absent.Furthermore,we also demonstrate the chemical substitution of V atoms with other elements such as Cr and Nb,showing a different modulation on the superconductivity phases and CDWs.These findings open up a way to synthesise a new family of doped CsV_(3)Sb_(5) materials,and further represent a new platform for tuning the different correlated electronic states and superconducting pairing in kagome superconductors.
