We perform ^(23)Na nuclear magnetic resonance(NMR) and magnetization measurements on an S=1,quasi-2D honeycomb lattice antiferromagnet Na_(3)Ni_(2)BiO_(6).A large positive Curie-Weiss constant of 22.9 K is observed.Th...We perform ^(23)Na nuclear magnetic resonance(NMR) and magnetization measurements on an S=1,quasi-2D honeycomb lattice antiferromagnet Na_(3)Ni_(2)BiO_(6).A large positive Curie-Weiss constant of 22.9 K is observed.The NMR spectra at low fields are consistent with a zigzag magnetic order,indicating a large easy-axis anisotropy.With the field applied along the c*axis,the NMR spectra confirm the existence of a 1/3-magnetization plateau phase between 5.1 T and 7.1 T.The transition from the zigzag order to the 1/3-magnetization plateau phase is also found to be a first-order type.A monotonic decrease of the spin gap is revealed in the 1/3-magnetization plateau phase,which reaches zero at a quantum critical field H_(C)≈8.35 T before entering the fully polarized phase.These data suggest the existence of exchange frustration in the system along with strong ferromagnetic interactions,hosting the possibility for Kitaev physics.Besides,well below the ordered phase,the 1/T_(1) at high fields shows either a level off or an enhancement upon cooling below 3 K,which suggests the existence of low-energy fluctuations.展开更多
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
Dirac nodal-line semimetals with the linear bands crossing along a line or loop, represent a new topological state of matter. Here, by carrying out magnetotransport measurements and performing first-principle calculat...Dirac nodal-line semimetals with the linear bands crossing along a line or loop, represent a new topological state of matter. Here, by carrying out magnetotransport measurements and performing first-principle calculations, we demonstrate that such a state has been realized in high-quality single crystals of SrAs_3.We obtain the nontrivial ∏ Berry phase by analysing the Shubnikov-de Haas quantum oscillations. We also observe a robust negative longitudinal magnetoresistance induced by the chiral anomaly.Accompanying first-principles calculations identifies that a single hole pocket enclosing the loop nodes is responsible for these observations.展开更多
In this study we successfully intercalated potassium(K) atoms into single ZrTe_5 crystals by liquid ammonia method, and found a semimetal-to-semiconductor transition at low temperatures in K-intercalated ZrTe_5. As th...In this study we successfully intercalated potassium(K) atoms into single ZrTe_5 crystals by liquid ammonia method, and found a semimetal-to-semiconductor transition at low temperatures in K-intercalated ZrTe_5. As the K concentration increased, the resistance anomalous peak was gradually suppressed until finally disappearing. Whilst, the corresponding Hall resistance measurements consistently showed a sign reversal. The semimetal-to-semiconductor transition can be attributed to a lattice expansion induced by atom intercalation, leading to a larger energy band gap.展开更多
The Kitaev model in a honeycomb lattice,which has an exactly solvable spin liquid as the ground state[1],has attracted a lot of research interests.Recently,Kitaev-type interactions were discovered in several quasi-2D,...The Kitaev model in a honeycomb lattice,which has an exactly solvable spin liquid as the ground state[1],has attracted a lot of research interests.Recently,Kitaev-type interactions were discovered in several quasi-2D,honeycomb lattice compounds,such as A_2IrO_3(A=Li,Na)[2-7]and α-RuCl_3[8-15].In these compounds,both the spin-orbit coupling and electron correlations play an essential role in the emergent Mott insulator behaviors[2,16-19].Although展开更多
Recently,the layered transition metal dichalcogenide 1T′-MoTe2 has generated considerable interest due to their superconducting and non-trivial topological properties.Here,we present a systematic study on 1T′-MoTe2 ...Recently,the layered transition metal dichalcogenide 1T′-MoTe2 has generated considerable interest due to their superconducting and non-trivial topological properties.Here,we present a systematic study on 1T′-MoTe2 single-crystal and exfoliated thin-flakes by means of electrical transport,scanning tunnelling microscope(STM)measurements and band structure calculations.For a bulk sample,it exhibits large magneto-resistance(MR)and Shubnikov–de Hass oscillations inρxx and a series of Hall plateaus inρxy at low temperatures.Meanwhile,the MoTe2 thin films were intensively investigated with thickness dependence.For samples,without encapsulation,an apparent transition from the intrinsic metallic to insulating state is observed by reducing thickness.In such thin films,we also observed a suppression of the MR and weak anti-localization(WAL)effects.We attributed these effects to disorders originated from the extrinsic surface chemical reaction,which is consistent with the density functional theory(DFT)calculations and in-situ STM results.In contrast to samples without encapsulated protection,we discovered an interesting superconducting transition for those samples with hexagonal Boron Nitride(h-BN)film protection.Our results indicate that the metallic or superconducting behavior is its intrinsic state,and the insulating behavior is likely caused by surface oxidation in few layer 1T’-MoTe2 flakes.展开更多
基金Project supported by the National Key R&D Program of China (Grant Nos. 2023YFA1406500, 2022YFA1402700, and 2021YFA1400400)the National Natural Science Foundation of China (Grant Nos. 12134020, 12374156, 12104503,12061131004, 12225407, and 12074174)。
文摘We perform ^(23)Na nuclear magnetic resonance(NMR) and magnetization measurements on an S=1,quasi-2D honeycomb lattice antiferromagnet Na_(3)Ni_(2)BiO_(6).A large positive Curie-Weiss constant of 22.9 K is observed.The NMR spectra at low fields are consistent with a zigzag magnetic order,indicating a large easy-axis anisotropy.With the field applied along the c*axis,the NMR spectra confirm the existence of a 1/3-magnetization plateau phase between 5.1 T and 7.1 T.The transition from the zigzag order to the 1/3-magnetization plateau phase is also found to be a first-order type.A monotonic decrease of the spin gap is revealed in the 1/3-magnetization plateau phase,which reaches zero at a quantum critical field H_(C)≈8.35 T before entering the fully polarized phase.These data suggest the existence of exchange frustration in the system along with strong ferromagnetic interactions,hosting the possibility for Kitaev physics.Besides,well below the ordered phase,the 1/T_(1) at high fields shows either a level off or an enhancement upon cooling below 3 K,which suggests the existence of low-energy fluctuations.
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 Natural Science Foundation of China(11674157,51372112 and 11574133)the National Key Research and Development Plan(2016YFA0300404)the National Basic Research Program of China(2015CB921202)
文摘Dirac nodal-line semimetals with the linear bands crossing along a line or loop, represent a new topological state of matter. Here, by carrying out magnetotransport measurements and performing first-principle calculations, we demonstrate that such a state has been realized in high-quality single crystals of SrAs_3.We obtain the nontrivial ∏ Berry phase by analysing the Shubnikov-de Haas quantum oscillations. We also observe a robust negative longitudinal magnetoresistance induced by the chiral anomaly.Accompanying first-principles calculations identifies that a single hole pocket enclosing the loop nodes is responsible for these observations.
基金supported by the Ministry of Science and Technology of China(Grant Nos.2014CB921103,and 2015CB921203)the National Natural Science Foundation of China(Grant Nos.11774149,11790311,11674157,11674154,51032003,1171101156,11374149,and 11374140)
文摘In this study we successfully intercalated potassium(K) atoms into single ZrTe_5 crystals by liquid ammonia method, and found a semimetal-to-semiconductor transition at low temperatures in K-intercalated ZrTe_5. As the K concentration increased, the resistance anomalous peak was gradually suppressed until finally disappearing. Whilst, the corresponding Hall resistance measurements consistently showed a sign reversal. The semimetal-to-semiconductor transition can be attributed to a lattice expansion induced by atom intercalation, leading to a larger energy band gap.
基金supported by the Ministry of Science and Technology of China(Grant No.2016YFA0300504)the National Natural Science Foundation of China(Grant No.11374364)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(Grant No.14XNLF08)
文摘The Kitaev model in a honeycomb lattice,which has an exactly solvable spin liquid as the ground state[1],has attracted a lot of research interests.Recently,Kitaev-type interactions were discovered in several quasi-2D,honeycomb lattice compounds,such as A_2IrO_3(A=Li,Na)[2-7]and α-RuCl_3[8-15].In these compounds,both the spin-orbit coupling and electron correlations play an essential role in the emergent Mott insulator behaviors[2,16-19].Although
基金The work was supported by the Guangdong Innovative and Entrepreneurial Research Team Program,China(Grant No.2016ZT06D348)the National Natural Science Foundation of China(Grant No.11874193)the Shenzhen Fundamental Subject Research Program,China(Grant No.JCYJ20170817110751776).K.D.W.acknowledges support from the National Natural Science Foundation of China(Grant No.11574128).X.D.acknowledges support from NSF under award DMR-1808491.
文摘Recently,the layered transition metal dichalcogenide 1T′-MoTe2 has generated considerable interest due to their superconducting and non-trivial topological properties.Here,we present a systematic study on 1T′-MoTe2 single-crystal and exfoliated thin-flakes by means of electrical transport,scanning tunnelling microscope(STM)measurements and band structure calculations.For a bulk sample,it exhibits large magneto-resistance(MR)and Shubnikov–de Hass oscillations inρxx and a series of Hall plateaus inρxy at low temperatures.Meanwhile,the MoTe2 thin films were intensively investigated with thickness dependence.For samples,without encapsulation,an apparent transition from the intrinsic metallic to insulating state is observed by reducing thickness.In such thin films,we also observed a suppression of the MR and weak anti-localization(WAL)effects.We attributed these effects to disorders originated from the extrinsic surface chemical reaction,which is consistent with the density functional theory(DFT)calculations and in-situ STM results.In contrast to samples without encapsulated protection,we discovered an interesting superconducting transition for those samples with hexagonal Boron Nitride(h-BN)film protection.Our results indicate that the metallic or superconducting behavior is its intrinsic state,and the insulating behavior is likely caused by surface oxidation in few layer 1T’-MoTe2 flakes.