In iron-based superconductors,the(0,π) or(π,0) nematicity,which describes an electronic anisotropy with a fourfold symmetry breaking,is well established and believed to be important for understanding the superconduc...In iron-based superconductors,the(0,π) or(π,0) nematicity,which describes an electronic anisotropy with a fourfold symmetry breaking,is well established and believed to be important for understanding the superconducting mechanism.However,how exactly such a nematic order observed in the normal state can be related to the superconducting pairing is still elusive.Here,by performing angular-dependent in-plane magnetoresistivity using ultra-thin flakes in the steep superconducting transition region,we unveil a nematic superconducting order along the(π,π) direction in electron-doped BaFe_(2-x)Ni_(x)As_(2) from under-doped to heavily overdoped regimes with x=0.065- 0.18.It shows superconducting gap maxima along the(π,π) direction rotated by 45° from the nematicity along(0, π) or(π,0) direction observed in the normal state.A similar(π,π)-type nematicity is also observed in the under-doped and optimally doped hole-type Ba1-yKyFe2 As_(2),with y=0.2-0.5.These results suggest that the(π,π) nematic superconducting order is a universal feature that needs to be taken into account in the superconducting pairing mechanism in iron-based superconductors.展开更多
We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which suppor...We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which supports the quantum Griffiths singularity in the Eu O/KTa O3 interface.The quantum Griffiths singularity could be attributed to large rare superconducting regions and quenched disorders at the interface.Our results could pave the way for studying the exotic superconducting properties at the Eu O/KTa O3 interface.展开更多
Grouping different oxide materials with coupled charge, spin, and orbital degrees of freedom together to form heterostructures provides a rich playground to explore the emergent interfacial phenomena. The perovskite/b...Grouping different oxide materials with coupled charge, spin, and orbital degrees of freedom together to form heterostructures provides a rich playground to explore the emergent interfacial phenomena. The perovskite/brownmillerite heterostructure is particularly interesting since symmetry mismatch may produce considerable interface reconstruction and unexpected physical effects. Here, we systemically study the magnetic anisotropy of tensely strained La2/3Sr1/3Co1-xMnxO2.5+δ/La2/3Sr1/3MnO3/La2/3Sr1/3Co1-xMnxO2.5+δ trilayers with interface structures changing from perovskite/brownmillerite type to perovskite/perovskite type. Without Mn doping, the initial La2/3Sr1/3CoO2.5+δ/La2/3Sr1/3MnO3/La2/3Sr1/3CoO2.5+δ trilayer with perovskite/brownmillerite interface type exhibits perpendicular magnetic anisotropy and the maximal anisotropy constant is 3.385×106 erg/cm3, which is more than one orders of magnitude larger than that of same strained LSMO film. By increasing the Mn doping concentration, the anisotropy constant displays monotonic reduction and even changes from perpendicular magnetic anisotropy to in-plane magnetic anisotropy, which is possible because of the reduced CoO4 tetrahedra concentration in the La2/3Sr1/3Co1-xMnxO2.5+δ layers near the interface. Based on the analysis of the x-ray linear dichroism, the orbital reconstruction of Mn ions occurs at the interface of the trilayers and thus results in the controllable magnetic anisotropy.展开更多
We construct a class of exactly solvable generalized Kitaev spin-1/2 models in arbitrary dimensions, which is beyond the category of quantum compass models. The Jordan-Wigner transformation is employed to prove the ex...We construct a class of exactly solvable generalized Kitaev spin-1/2 models in arbitrary dimensions, which is beyond the category of quantum compass models. The Jordan-Wigner transformation is employed to prove the exact solvability. An exactly solvable quantum spin-1/2 model can be mapped to a gas of free Majorana fermions coupled to static Z2 gauge fields. We classify these exactly solvable models according to their parent models. Any model belonging to this class can be generated by one of the parent models. For illustration, a two dimensional(2D) tetragon-octagon model and a three dimensional(3D) xy bond model are studied.展开更多
2D MoTe_(2),WTe_(2) and their alloys have received intensive research interest because of their unique properties arising from the polymorph structures,chiral anomaly,strong spin-orbit coupling,and so on.In this revie...2D MoTe_(2),WTe_(2) and their alloys have received intensive research interest because of their unique properties arising from the polymorph structures,chiral anomaly,strong spin-orbit coupling,and so on.In this review,we have summarized recent advances of 2D MoTe_(2),WTe_(2) and their alloys from the materials perspective with special focus on the synthesis,electrical and magnetic properties.The polymorph structures of MoTe_(2),WTe_(2) and their alloys are presented first and then the preparation methods have been discussed,including mechanical exfoliation,metal-organic chemical vapor deposition(MOCVD),molecular beam epitaxy(MBE),chemical vapor deposition(CVD)and solution-phase method.After that,fascinating physical properties arising from the large spin-orbit coupling and non-trivial band structures have been summarized,including phase transition,optoelectri-cal properties,Weyl semimetal state,superconducting and ferromagnetism.At last,potential device applications of MoTe_(2),WTe_(2) and their alloys are reviewed,including field-effect transistors(FETs),memory devices,spin-to-charge conversion,solar cells,and so on.展开更多
基金Supported by the National Natural Science Foundation of China(Grant Nos.61771234,61727805,11674157,11674158,11774152,11822405,61521001,6157121961501222)+6 种基金the National Key Projects for Research and Development of China(Grant Nos.2016YFA0300401,2017YFB0503302,2017YFA03040022017YFB0503300)the start-up funding from ShanghaiTech University,Innovative Research Team in University(PCSIRT)the Natural Science Foundation of Shanghai Municipality(Grant No.20ZR1436100)the Science and Technology Commission of Shanghai Municipality(Grant No.YDZX20203100001438)Jiangsu Key Laboratory of Advanced Techniques for Manipulating Electromagnetic Waves,Natural Science Foundation of Jiangsu Province(Grant No.BK20180006)the Fundamental Research Funds for the Central Universities(Grant No.020414380117)。
文摘In iron-based superconductors,the(0,π) or(π,0) nematicity,which describes an electronic anisotropy with a fourfold symmetry breaking,is well established and believed to be important for understanding the superconducting mechanism.However,how exactly such a nematic order observed in the normal state can be related to the superconducting pairing is still elusive.Here,by performing angular-dependent in-plane magnetoresistivity using ultra-thin flakes in the steep superconducting transition region,we unveil a nematic superconducting order along the(π,π) direction in electron-doped BaFe_(2-x)Ni_(x)As_(2) from under-doped to heavily overdoped regimes with x=0.065- 0.18.It shows superconducting gap maxima along the(π,π) direction rotated by 45° from the nematicity along(0, π) or(π,0) direction observed in the normal state.A similar(π,π)-type nematicity is also observed in the under-doped and optimally doped hole-type Ba1-yKyFe2 As_(2),with y=0.2-0.5.These results suggest that the(π,π) nematic superconducting order is a universal feature that needs to be taken into account in the superconducting pairing mechanism in iron-based superconductors.
基金Supported by the National Key R&D Program of China(Grant Nos.2019YFA0308401 and 2017YFA0303301)the National Natural Science Foundation of China(Grant Nos.11974025,11674009,and 11934016)+1 种基金the Beijing Natural Science Foundation(Grant No.1192009)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB28000000)。
文摘We report the experimental investigation of the superconductor-metal quantum phase transition of the Eu O/KTa O3 interface.Around the transition,a divergence of the dynamical critical exponent is observed,which supports the quantum Griffiths singularity in the Eu O/KTa O3 interface.The quantum Griffiths singularity could be attributed to large rare superconducting regions and quenched disorders at the interface.Our results could pave the way for studying the exotic superconducting properties at the Eu O/KTa O3 interface.
基金Project supported by the National Basic Research Program of China(Grant Nos.2016YFA0300701,2017YFA0206300,2017YFA0303601,and 2018YFA0305704)the National Natural Science Foundation of China(Grant Nos.11520101002,51590880,11674378,11934016,and 51972335)the Key Program of the Chinese Academy of Sciences.
文摘Grouping different oxide materials with coupled charge, spin, and orbital degrees of freedom together to form heterostructures provides a rich playground to explore the emergent interfacial phenomena. The perovskite/brownmillerite heterostructure is particularly interesting since symmetry mismatch may produce considerable interface reconstruction and unexpected physical effects. Here, we systemically study the magnetic anisotropy of tensely strained La2/3Sr1/3Co1-xMnxO2.5+δ/La2/3Sr1/3MnO3/La2/3Sr1/3Co1-xMnxO2.5+δ trilayers with interface structures changing from perovskite/brownmillerite type to perovskite/perovskite type. Without Mn doping, the initial La2/3Sr1/3CoO2.5+δ/La2/3Sr1/3MnO3/La2/3Sr1/3CoO2.5+δ trilayer with perovskite/brownmillerite interface type exhibits perpendicular magnetic anisotropy and the maximal anisotropy constant is 3.385×106 erg/cm3, which is more than one orders of magnitude larger than that of same strained LSMO film. By increasing the Mn doping concentration, the anisotropy constant displays monotonic reduction and even changes from perpendicular magnetic anisotropy to in-plane magnetic anisotropy, which is possible because of the reduced CoO4 tetrahedra concentration in the La2/3Sr1/3Co1-xMnxO2.5+δ layers near the interface. Based on the analysis of the x-ray linear dichroism, the orbital reconstruction of Mn ions occurs at the interface of the trilayers and thus results in the controllable magnetic anisotropy.
基金the China Postdoctoral Science Foundation of China(Grant No.2017M620880)the National Natural Science Foundation of China(Grant No.1184700424)+7 种基金the National Key Research and Development Program of China(Grant No.2016YFA0300202)the National Basic Research Program of China(Grant No.2014CB921201)the National Natural Science Foundation of Chino(Grant No.11774306)the Key Research Program of the Chinese Academy of Sciences(Grant No.XDPB08-4)the Fundamental Research Funds for the Central Universities in Chinathe National Natural Science Foundation of China(Grant No.11674278)the National Basic Research Program of China(Grant No.2014CB921203)the CAS Center for Excellence in Topological Quantum Computation.
文摘We construct a class of exactly solvable generalized Kitaev spin-1/2 models in arbitrary dimensions, which is beyond the category of quantum compass models. The Jordan-Wigner transformation is employed to prove the exact solvability. An exactly solvable quantum spin-1/2 model can be mapped to a gas of free Majorana fermions coupled to static Z2 gauge fields. We classify these exactly solvable models according to their parent models. Any model belonging to this class can be generated by one of the parent models. For illustration, a two dimensional(2D) tetragon-octagon model and a three dimensional(3D) xy bond model are studied.
基金support from NSFC(21822502)the Key Research Program of Frontier Sciences of CAS(QYZDB-SSWSYS031)+1 种基金the Strategic Priority Research Program of CAS(XDB30000000)Y.C.acknowledges support from the National Basic Research of China(2017YFA0206300)and NSFC(51972335).
文摘2D MoTe_(2),WTe_(2) and their alloys have received intensive research interest because of their unique properties arising from the polymorph structures,chiral anomaly,strong spin-orbit coupling,and so on.In this review,we have summarized recent advances of 2D MoTe_(2),WTe_(2) and their alloys from the materials perspective with special focus on the synthesis,electrical and magnetic properties.The polymorph structures of MoTe_(2),WTe_(2) and their alloys are presented first and then the preparation methods have been discussed,including mechanical exfoliation,metal-organic chemical vapor deposition(MOCVD),molecular beam epitaxy(MBE),chemical vapor deposition(CVD)and solution-phase method.After that,fascinating physical properties arising from the large spin-orbit coupling and non-trivial band structures have been summarized,including phase transition,optoelectri-cal properties,Weyl semimetal state,superconducting and ferromagnetism.At last,potential device applications of MoTe_(2),WTe_(2) and their alloys are reviewed,including field-effect transistors(FETs),memory devices,spin-to-charge conversion,solar cells,and so on.
基金supported by the National Key Research and Development Program of Ministry of Science and Technology of China (2017YFA0303002, 2016YFA0300204, and 2016YFA0300701)the Fundamental Research Funds for the Central Universities
基金the National Key R&D Program of China(2016FYA0300402 and 2017YFA0303101)the National Natural Science Foundation of China(NSFC)(11674279 and 11374257)+8 种基金supported in part by the NSFC(U1732162 and 11974061)support from the Zhejiang Provincial Natural Science Foundation(LR18A04001)supported in part by the National Key Research and Development Program of China(2016YFA0300202)the National Natural Science Foundation of China(11774306)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB28000000)partly supported by KAKENHI(JP20H05164,19K14661,15H05883,18H01161,and JP17K05553)from JSPS‘‘JPhysics”(18H04306)financial support provided by the Project Number MOST-108-2112-M-001-049-MY2the Academia Sinica for the budget of AS-iMATE-109-13。