MnBi_(2)Te_(4),which is emerging as an intrinsic antiferromagnetic(AFM)topological insulator,provides a unique platform to investigate the interplay between magnetism and topology.Modulating its magnetic properties en...MnBi_(2)Te_(4),which is emerging as an intrinsic antiferromagnetic(AFM)topological insulator,provides a unique platform to investigate the interplay between magnetism and topology.Modulating its magnetic properties enables the observation of exotic quantum phenomena such as the quantum anomalous Hall effect,axion insulator states,and Majorana fermions.While the intercalation of Bi_(2)Te_(3)can tune its magnetism,synthesizing pure-phase MnBi_(2)Te_(4)with uniform Bi_(2)Te_(3)intercalation remains challenging,and the fixed interlayer spacing of Bi_(2)Te_(3)limits magnetic coupling tunability.Here,we utilize electrochemical organic molecule intercalation to expand the van der Waals gap of MnBi_(2)Te_(4)and modulate its magnetic properties.Through x-ray diffraction(XRD)characterizations,we confirm that the interlayer spacing of MnBi_(2)Te_(4)is expanded from 13.6°A to 30.5°A and 61.0°A by intercalating quaternary ammonium cations(THA^(+)and CTA^(+)),respectively.The THA-MnBi_(2)Te_(4)exhibits dual complex magnetic behavior,combining AFM ordering with a Neel temperature(T_(N))of 12 K and a small ferromagnetic hysteresis loop at 2 K.The CTA-MnBi_(2)Te_(4)shows robust ferromagnetism,with a Curie point(T_(C))of 15 K,similar to that of the MnBi_(2)Te_(4)monolayer.These results demonstrate that remarkable changes in the magnetic properties of MnBi_(2)Te_(4)can be achieved via electrochemical intercalation,providing new insights into manipulating magnetism in layered magnetic materials.展开更多
Naturally existing in-plane hyperbolic polaritons and the associated optical topological transitions,which avoid the nano-structuring to achieve hyperbolicity,can outperform their counterparts in artificial metasurfac...Naturally existing in-plane hyperbolic polaritons and the associated optical topological transitions,which avoid the nano-structuring to achieve hyperbolicity,can outperform their counterparts in artificial metasurfaces.Such plasmon polaritons are rare,but experimentally revealed recently in WTe_(2)van der Waals thin films.Different from phonon polaritons,hyperbolic plasmon polaritons originate from the interplay of free carrier Drude response and interband transitions,which promise good intrinsic tunability.However,tunable in-plane hyperbolic plasmon polariton and its optical topological transition of the isofrequency contours to the elliptic topology in a natural material have not been realized.Here we demonstrate the tuning of the optical topological transition through Mo doping and temperature.The optical topological transition energy is tuned over a wide range,with frequencies ranging from 429 cm^(−1)(23.3 microns)for pure WTe_(2)to 270 cm^(−1)(37.0 microns)at the 50%Mo-doping level at 10 K.Moreover,the temperature-induced blueshift of the optical topological transition energy is also revealed,enabling active and reversible tuning.Surprisingly,the localized surface plasmon resonance in skew ribbons shows unusual polarization dependence,accurately manifesting its topology,which renders a reliable means to track the topology with far-field techniques.Our results open an avenue for reconfigurable photonic devices capable of plasmon polariton steering,such as canaling,focusing,and routing,and pave the way for low-symmetry plasmonic nanophotonics based on anisotropic natural materials.展开更多
Kagome lattice,characterized by two-dimensional honeycomb network of corner-sharing triangles[1],presents flat bands,Dirac cones,and van Hove singularities(VHSs),which have been theoretically predicted and experimenta...Kagome lattice,characterized by two-dimensional honeycomb network of corner-sharing triangles[1],presents flat bands,Dirac cones,and van Hove singularities(VHSs),which have been theoretically predicted and experimentally observed[2-4].When combined with spin-orbit coupling(SOC)and magnetism,novel properties have emerged.Although kagome materials vary,most of their strong interlayer interactions make the synthesized crystals not layered,and the properties deviating from the raw two-dimensional kagome lattices.These crystals are difficult to fabricate into thin devices and to tune the physical properties of the materials using gate voltage.展开更多
基金supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1402404 and 2023YFA1406304)the National Natural Science Foundation of China(Grant Nos.92161201,T2221003,12104221,12104220,12274208,12025404,12004174,91961101,T2394473,62274085,12374043,and U2032208)+1 种基金the Natural Science Foundation of Jiangsu Province(Grant Nos.BK20230079,BK20243013,and BK20233001)the Fundamental Research Funds for the Central Universities(Grant Nos.020414380192 and 2024300432).
文摘MnBi_(2)Te_(4),which is emerging as an intrinsic antiferromagnetic(AFM)topological insulator,provides a unique platform to investigate the interplay between magnetism and topology.Modulating its magnetic properties enables the observation of exotic quantum phenomena such as the quantum anomalous Hall effect,axion insulator states,and Majorana fermions.While the intercalation of Bi_(2)Te_(3)can tune its magnetism,synthesizing pure-phase MnBi_(2)Te_(4)with uniform Bi_(2)Te_(3)intercalation remains challenging,and the fixed interlayer spacing of Bi_(2)Te_(3)limits magnetic coupling tunability.Here,we utilize electrochemical organic molecule intercalation to expand the van der Waals gap of MnBi_(2)Te_(4)and modulate its magnetic properties.Through x-ray diffraction(XRD)characterizations,we confirm that the interlayer spacing of MnBi_(2)Te_(4)is expanded from 13.6°A to 30.5°A and 61.0°A by intercalating quaternary ammonium cations(THA^(+)and CTA^(+)),respectively.The THA-MnBi_(2)Te_(4)exhibits dual complex magnetic behavior,combining AFM ordering with a Neel temperature(T_(N))of 12 K and a small ferromagnetic hysteresis loop at 2 K.The CTA-MnBi_(2)Te_(4)shows robust ferromagnetism,with a Curie point(T_(C))of 15 K,similar to that of the MnBi_(2)Te_(4)monolayer.These results demonstrate that remarkable changes in the magnetic properties of MnBi_(2)Te_(4)can be achieved via electrochemical intercalation,providing new insights into manipulating magnetism in layered magnetic materials.
基金H.Y.is grateful to the financial support from the National Key Research and Development Program of China(Grant Nos.2022YFA1404700 and 2021YFA1400100)the National Natural Science Foundation of China(Grant No.12074085)+7 种基金the Natural Science Foundation of Shanghai(Grant No.23XD1400200)C.W.is grateful to the financial support from the National Natural Science Foundation of China(Grant Nos.12274030,11704075)the National Key Research and Development Program of China(Grant No.2022YFA1403400)F.S.acknowledges the financial support from the National Key Research and Development Program of China(Grant No.2017YFA0303203)the National Natural Science Foundation of China(Grant Nos.92161201,12025404,11904165,and 12274208)the Natural Science Foundation of Jiangsu Province(Grant No.BK20190286)S.H.is grateful to the financial support from the China Postdoctoral Science Foundation(Grant No.2020TQ0078)Part of the experimental work was carried out in Fudan Nanofabrication Lab.
文摘Naturally existing in-plane hyperbolic polaritons and the associated optical topological transitions,which avoid the nano-structuring to achieve hyperbolicity,can outperform their counterparts in artificial metasurfaces.Such plasmon polaritons are rare,but experimentally revealed recently in WTe_(2)van der Waals thin films.Different from phonon polaritons,hyperbolic plasmon polaritons originate from the interplay of free carrier Drude response and interband transitions,which promise good intrinsic tunability.However,tunable in-plane hyperbolic plasmon polariton and its optical topological transition of the isofrequency contours to the elliptic topology in a natural material have not been realized.Here we demonstrate the tuning of the optical topological transition through Mo doping and temperature.The optical topological transition energy is tuned over a wide range,with frequencies ranging from 429 cm^(−1)(23.3 microns)for pure WTe_(2)to 270 cm^(−1)(37.0 microns)at the 50%Mo-doping level at 10 K.Moreover,the temperature-induced blueshift of the optical topological transition energy is also revealed,enabling active and reversible tuning.Surprisingly,the localized surface plasmon resonance in skew ribbons shows unusual polarization dependence,accurately manifesting its topology,which renders a reliable means to track the topology with far-field techniques.Our results open an avenue for reconfigurable photonic devices capable of plasmon polariton steering,such as canaling,focusing,and routing,and pave the way for low-symmetry plasmonic nanophotonics based on anisotropic natural materials.
基金National Key Research and Development Program of China(2022YFA1402404)National Natural Science Foundation of China(92161201,T2221003,12104221,12104220,12274208,12025404,12004174,91961101,61822403,11874203,and 12374043)+1 种基金Natural Science Foundation of Jiangsu Province(BK20230079)Fundamental Research Funds for the Central Universities(020414380192 and 2024300432)。
文摘Kagome lattice,characterized by two-dimensional honeycomb network of corner-sharing triangles[1],presents flat bands,Dirac cones,and van Hove singularities(VHSs),which have been theoretically predicted and experimentally observed[2-4].When combined with spin-orbit coupling(SOC)and magnetism,novel properties have emerged.Although kagome materials vary,most of their strong interlayer interactions make the synthesized crystals not layered,and the properties deviating from the raw two-dimensional kagome lattices.These crystals are difficult to fabricate into thin devices and to tune the physical properties of the materials using gate voltage.
