Recent advancements in two-dimensional van der Waals moir´e materials have unveiled the captivating landscape of moir´e physics.In twisted bilayer graphene(TBG)at‘magic angles’,strong electronic correlatio...Recent advancements in two-dimensional van der Waals moir´e materials have unveiled the captivating landscape of moir´e physics.In twisted bilayer graphene(TBG)at‘magic angles’,strong electronic correlations give rise to a diverse array of exotic physical phenomena,including correlated insulating states,superconductivity,magnetism,topological phases,and the quantum anomalous Hall(QAH)effect.Notably,the QAH effect demonstrates substantial promise for applications in electronic and quantum computing devices with low power consumption.This article focuses on the latest developments surrounding the QAH effect in magic-angle TBG.It provides a comprehensive analysis of magnetism and topology—two crucial factors in engineering the QAH effect within magic-angle TBG.Additionally,it offers a detailed overview of the experimental realization of the QAH effect in moir´e superlattices.Furthermore,this review highlights the underlying mechanisms driving these exotic phases in moir´e materials,contributing to a deeper understanding of strongly interacting quantum systems and facilitating the manipulation of new material properties to achieve novel quantum states.展开更多
Optical singularities are topological defects of electromagnetic fields;they include phase singularity in scalar fields,polarization singularity in vector fields,and three-dimensional(3D)singularities such as optical ...Optical singularities are topological defects of electromagnetic fields;they include phase singularity in scalar fields,polarization singularity in vector fields,and three-dimensional(3D)singularities such as optical skyrmions.The exploitation of photonic microstructures to generate and manipulate optical singularities has attracted wide research interest in recent years,with many photonic microstructures having been devised to this end.Accompanying these designs,scattered phenomenological theories have been proposed to expound the working mechanisms behind individual designs.In this work,instead of focusing on a specific type of microstructure,we concentrate on the most common geometric features of these microstructures—namely,symmetries—and revisit the process of generating optical singularities in microstructures from a symmetry viewpoint.By systematically employing the projection operator technique in group theory,we develop a widely applicable theoretical scheme to explore optical singularities in microstructures with rosette(i.e.,rotational and reflection)symmetries.Our scheme agrees well with previously reported works and further reveals that the eigenmodes of a symmetric microstructure can support multiplexed phase singularities in different components,such as out-of-plane,radial,azimuthal,and left-and right-handed circular components.Based on these phase singularities,more complicated optical singularities may be synthesized,including C points,V points,L lines,Néel-and bubble-type optical skyrmions,and optical lattices,to name a few.We demonstrate that the topological invariants associated with optical singularities are protected by the symmetries of the microstructure.Lastly,based on symmetry arguments,we formulate a so-called symmetry matching condition to clarify the excitation of a specific type of optical singularity.Our work establishes a unified theoretical framework to explore optical singularities in photonic microstructures with symmetries,shedding light on the symmetry origin of multidimensional and multiplexed optical singularities and providing a symmetry perspective for exploring many singularity-related effects in optics and photonics.展开更多
Two-dimensional Fourier transform(2D FT) spectroscopy is an important technology that developed in recent decades and has many advantages over other ultrafast spectroscopy methods. Although 2D FT spectroscopy provides...Two-dimensional Fourier transform(2D FT) spectroscopy is an important technology that developed in recent decades and has many advantages over other ultrafast spectroscopy methods. Although 2D FT spectroscopy provides great opportunities for studying various complex systems, the experimental implementation and theoretical description of 2D FT spectroscopy measurement still face many challenges, which limits their wide application.Recently, the 2D FT spectroscopy reaches maturity due to many new developments which greatly reduces the technical barrier in the experimental implementation of the 2D FT spectrometer. There have been several different approaches developed for the optical design of the 2D FT spectrometer, each with its own advantages and limitations. Thus, a procedure to help an experimentalist to build a 2D FT spectroscopy experimental apparatus is needed.This tutorial review is intending to provide an accessible introduction for a beginner to build a 2D FT spectrometer.展开更多
Using the linear local induction approximation, we investigate the self-induced motion of a vortex-line that corresponds to the motion of a particle in quantum mechanics. Provided Kelvin waves, the effective Schr?ding...Using the linear local induction approximation, we investigate the self-induced motion of a vortex-line that corresponds to the motion of a particle in quantum mechanics. Provided Kelvin waves, the effective Schr?dinger equation, physical quantity operators, and the corresponding path-integral formula can be obtained. In particular,the effective Planck constant defined by parameters of vortex-line motion shows the mathematical relation between the two fields. The vortexline–particle mapping may help in understanding particle motion in quantum mechanics.展开更多
Tryptophan derivatives have long been used as site-specific biological probes. 4-Cyanotrypto- phan emits in the visible region and is the smallest blue fluorescent amino acid probe for bio- logical applications. Other...Tryptophan derivatives have long been used as site-specific biological probes. 4-Cyanotrypto- phan emits in the visible region and is the smallest blue fluorescent amino acid probe for bio- logical applications. Other indole or tryptophan analogs may emit at even longer wavelengths than 4-cyanotryptophan. We performed FTIR, UV-Vis, and steady-state and time-resolved fluorescence spectroscopy on six ester-derivatized indoles in different solvents. Methyl indole- 4-carboxylate emits at 450 nrn with a long fluorescence lifetirne, and is a promising candidate for a fluorescent probe. The ester-derivatized indoles could be used as spectroscopic probes to study local protein environments. Our measurements provide a guide for choosing esterderivatized indoles to use in practice and data for computational modeling of the effect of substitution on the electronic transitions of indole.展开更多
We design two new layered indium halide compounds LaOInF_(2)and LaOInCl_(2)by means of first-principles calculations and evolutionary crystal structure prediction.We find both compounds crystallize in a tetragonal str...We design two new layered indium halide compounds LaOInF_(2)and LaOInCl_(2)by means of first-principles calculations and evolutionary crystal structure prediction.We find both compounds crystallize in a tetragonal structure with P4/nmm space group and have indirect band gaps of 2.58 eV and 3.21 eV,respectively.By substituting O with F,both of them become metallic and superconducting at low temperature.The F-doping leads to strong electron-phonon coupling in the low-energy acoustic phonon modes which is mainly responsible for the induced superconductivity.The total electron-phonon coupling strength are 1.86 and 1.48,while the superconducting transition temperature(T_(c))are about 7.2 K and 6.5 K with 10%and 5%F doping for LaOInF_(2)and LaOInCl_(2),respectively.展开更多
Uniaxial strain is a powerful tuning parameter that can control symmetry and anisotropic electronic properties in iron-based superconductors.However,accurately characterizing anisotropic strain can be challenging and ...Uniaxial strain is a powerful tuning parameter that can control symmetry and anisotropic electronic properties in iron-based superconductors.However,accurately characterizing anisotropic strain can be challenging and complex.Here,we utilize a cryogenic optical system equipped with a high-spatial-resolution microscope to characterize surface strains in iron-based superconductors using the digital image correlation method.Compared with other methods such as high-resolution x-ray diffraction,strain gauge,and capacitive sensor,digital image correlation offers a non-contact full-field measurement approach,acting as an optical virtual strain gauge that provides high spatial resolution.The results measured on detwinned BaFe_(2)As_(2)are quantitatively consistent with the distortion measured by x-ray diffraction and neutron Larmor diffraction.These findings highlight the potential of cryogenic digital image correlation as an effective and accessible tool for probing the isotropic and anisotropic strains,facilitating applications of uniaxial strain tuning in research of quantum materials.展开更多
Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high-Tc superconductors.In iron-based superconductors,spin excitations at low energy range,especially the spin-resona...Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high-Tc superconductors.In iron-based superconductors,spin excitations at low energy range,especially the spin-resonance mode at ER~5kBTc,are important for understanding the superconductivity.Here,we use inelastic neutron scattering(INS)to investigate the symmetry and in-plane wave-vector dependence of low-energy spin excitations in uniaxial-strain detwinned Fe Se.The low-energy spin excitations(E<10 meV)appear mainly at Q=(±1,0)in the superconducting state(T9K)and the nematic state(T90 K),confirming the constant C_(2) rotational symmetry and ruling out the C_(4) mode at E≈3 meV reported in a prior INS study.Moreover,our results reveal an isotropic spin resonance in the superconducting state,which is consistent with the s±wave pairing symmetry.At slightly higher energy,low-energy spin excitations become highly anisotropic.The full width at half maximum of spin excitations is elongated along the transverse direction.The Q-space isotropic spin resonance and highly anisotropic low-energy spin excitations could arise from dyz intra-orbital selective Fermi surface nesting between the hole pocket aroundΓpoint and the electron pockets centered at MX point.展开更多
Determination of the magnetic structure and confirmation of the presence or absence of inversion(P)and time reversal(Τ)symmetry is imperative for correctly understanding the topological magnetic materials.Here highqu...Determination of the magnetic structure and confirmation of the presence or absence of inversion(P)and time reversal(Τ)symmetry is imperative for correctly understanding the topological magnetic materials.Here highquality single crystals of the layered manganese pnictide CaMnSb_(2)are synthesized using the self-flux method.展开更多
Understanding the effect of intermolecular interaction on the growth dynamic of active layers is critical for advancing organic solar cells(OSCs).However,the diverse structure of donors and acceptors makes the researc...Understanding the effect of intermolecular interaction on the growth dynamic of active layers is critical for advancing organic solar cells(OSCs).However,the diverse structure of donors and acceptors makes the research challenging.Additives with customizable structures and properties could simplify this complexity.Herein,we meticulously tailor two additives of 3,4-ethylenedioxythiophene(EDOT)and 2,5-dibromo-3,4-ethylenedioxythiophene(DBEDOT),possessing distinct intermolecular interaction features to elaborate the inherent relationship.It is found that varied interaction strengths can alter film formation processes.The enhanced intermolecular interaction between the DBEDOT and non-fullerene acceptor BTP-e C9-4F results in pre-aggregation and longer crystallization duration of BTP-e C9-4F,facilitating the formation of films with compact molecular packing and decent phase separation.Thus,exciton dissociation and charge transport become more efficient.Finally,devices processed with DBEDOT exhibit a remarkable power conversion efficiency of 19.35%in small-area OSCs and 14.11%in bladecoated 5 cm×5 cm organic solar mini-modules.Especially,OSCs can maintain 80%of their initial efficiency after continuous annealing at 85℃for over 2,100 h.展开更多
Breakdown of bulk-boundary correspondence in non-Hermitian(NH)topological systems with generalized inversion symmetries is a controversial issue.The non-Bloch topological invariants determine the existence of edge sta...Breakdown of bulk-boundary correspondence in non-Hermitian(NH)topological systems with generalized inversion symmetries is a controversial issue.The non-Bloch topological invariants determine the existence of edge states,but fail to describe the number and distribution of defective edge states in non-Hermitian topological systems.The state-dependent topological invariants,instead of a global topological invariant,are developed to accurately characterize the bulk-boundary correspondence of the NH systems,which is very different from their Hermitian counterparts.At the same time,we obtain the accurate phase diagram of the one-dimensional non-Hermitian Su–Schrieffer–Heeger model with a generalized inversion symmetry from the state-dependent topological invariants.Therefore,these results will be helpful for understanding the exotic topological properties of various non-Hermitian systems.展开更多
The side-chain has a significant influence on the optical properties and aggregation behaviors of the organic small molecule acceptors,which becomes an important strategy to optimize the photovoltaic performance of or...The side-chain has a significant influence on the optical properties and aggregation behaviors of the organic small molecule acceptors,which becomes an important strategy to optimize the photovoltaic performance of organic solar cells.In this work,we designed and synthesized three brand-new nonfused ring electron acceptors(NFREAs)OC4-4Cl-Ph,OC4-4Cl-Th,and OC4-4Cl-C8 with hexylbenzene,hexylthiophene,and octyl side chains on theπ-bridge units.Compared with OC4-4Cl-Ph and OC4-4Cl-Th,OC4-4Cl-C8 with linear alkyl side chain has more red-shift absorption,which is conducive to obtaining higher short-circuit current density.Additionally,the OC4-4Cl-C8 film exhibits a longer exciton diffusion distance,and the D18:OC4-4Cl-C8 blend film displays faster hole transfer,weaker bimolecular recombination,and more efficient exciton transport.Furthermore,The D18:OC4-4Cl-C8 blend films may effectively form interpenetrating networks that resemble nanofibrils,which can facilitate exciton dissociation and charge transport.Finally,OC4-4Cl-C8-based devices can be created a marvellously power conversion efficiency(PCE)of 16.56%,which is much higher than OC4-4Cl-Ph(12.29%)-and OC4-4Cl-Th-based(11.00%)ones,being the highest PCE among the NFREA based binary devices.All in all,we have validated that side-chain engineering is an efficient way to achieve high-performance NFREAs.展开更多
The in-plane magnetotransport of detwinned EuFe2As2 single crystal has been investigated.In the antiferromagnetic phase of Eu^2+spins,very different magnetoresistance results are observed upon the change of the extern...The in-plane magnetotransport of detwinned EuFe2As2 single crystal has been investigated.In the antiferromagnetic phase of Eu^2+spins,very different magnetoresistance results are observed upon the change of the external magnetic field direction and the current direction.This could be attributed to the tunable orientation of the Eu^2+spins under magnetic field.Electron scattering by spin fluctuation,superzone boundary effect,and cyclotron motion of charge carriers are used to interpret the observed anomalous magnetoresistance which is measured by using a current along a direction.The remarkable features of magnetoresistance suggest that itinerant electrons strongly couple with the spin configuration of Eu^2+,which has a huge influence on the transport properties of EuFe2As2.展开更多
The emergent van der Waals magnetic material is a promising component for spintronic devices with novel functionalities.Here,we report a transition of negative-to-positive magnetoresistance in Fe_(3)GeTe_(2)/Cr_(2)Ge_...The emergent van der Waals magnetic material is a promising component for spintronic devices with novel functionalities.Here,we report a transition of negative-to-positive magnetoresistance in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)van der Waals all-magnetic tunnel junctions with increasing the applied bias voltage.A negative magnetoresistance is observed first in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)tunnel junctions,where the resistance with antiparallel aligned magnetization of two Fe_(3)GeTe_(2)electrodes is lower than that with parallel alignment,which is due to the opposite spin polarizations of two Fe_(3)GeTe_(2)electrodes.With the bias voltage increasing,the spin polarization of the biased Fe_(3)GeTe_(2)electrode is changed so that the spin orientations of two Fe_(3)GeTe_(2)electrodes are the same.Our experimental observations are supported by the calculated spin-dependent density of states for Fe_(3)GeTe_(2)electrodes under a finite bias.The significantly bias voltage-dependent spin transport properties in van der Waals magnetic tunnel junctions open a promising route for designing electrical controllable spintronic devices based on van der Waals magnets.展开更多
The electronic properties of van der Waals(vd W) structures can be substantially modified by the moiré superlattice potential, which strongly depends on the twist angle among the compounds. In twisted bilayer gra...The electronic properties of van der Waals(vd W) structures can be substantially modified by the moiré superlattice potential, which strongly depends on the twist angle among the compounds. In twisted bilayer graphene(TBG), two lowenergy Van Hove singularities(VHSs) move closer with decreasing twist angles and finally become highly non-dispersive flat bands at the magic angle(~1.1°). When the Fermi level lies within the flat bands of the TBG near the magic angle,Coulomb interaction is supposed to exceed the kinetic energy of the electrons, which can drive the system into various strongly correlated phases. Moreover, the strongly correlated states of flat bands are also realized in other graphene-based vd W structures with an interlayer twist. In this article, we mainly review the recent scanning tunneling microscopy(STM)advances on the strongly correlated physics of the magic-angle TBG(MATBG) and the small-angle twisted multilayer graphene. Lastly we will give out a perspective of this field.展开更多
Electrons in graphene have fourfold spin and valley degeneracies owing to the unique bipartite honeycomb lattice and an extremely weak spin-orbit coupling,which can support a series of broken symmetry states.Atomic-sc...Electrons in graphene have fourfold spin and valley degeneracies owing to the unique bipartite honeycomb lattice and an extremely weak spin-orbit coupling,which can support a series of broken symmetry states.Atomic-scale defects in graphene are expected to lift these degenerate degrees of freedom at the nanoscale,and hence,lead to rich quantum states,highlighting promising directions for spintronics and valleytronics.In this article,we mainly review the recent scanning tunneling microscopy(STM)advances on the spin and/or valley polarized states induced by an individual atomicscale defect in graphene,including a single-carbon vacancy,a nitrogen-atom dopant,and a hydrogen-atom chemisorption.Lastly,we give a perspective in this field.展开更多
The kagome superconductor CsV_(3)Sb_(5) with exotic electronic properties has attracted substantial research interest,and the interplay between the superconductivity and the charge-density wave is crucial for understa...The kagome superconductor CsV_(3)Sb_(5) with exotic electronic properties has attracted substantial research interest,and the interplay between the superconductivity and the charge-density wave is crucial for understanding its unusual electronic ground state.In this work,we performed resistivity and AC magnetic susceptibility measurements on CsV_(3)Sb_(5) single crystals uniaxially-strained along[100]and[110]directions.We find that the uniaxial-strain tuning effect of T_(c)(dT_(c)/dε)and T_(CDW)(dT_(CDW)/dε)are almost identical along these distinct high-symmetry directions.These findings suggest the in-plane uniaxial-strain-tuning of T_(c) and T_(CDW)in CsV_(3)Sb_(5) are dominated by associated c-axis strain,whereas the response to purely in-plane strains is likely small.展开更多
The imaginary time path integral formalism offers a powerful numerical tool for simulating thermodynamic properties of realistic systems.We show that,when second-order and fourth-order decompositions are employed,they...The imaginary time path integral formalism offers a powerful numerical tool for simulating thermodynamic properties of realistic systems.We show that,when second-order and fourth-order decompositions are employed,they share a remarkable unified analytic form for the partition function of the harmonic oscillator.We are then able to obtain the expression of the thermodynamic property and the leading error terms as well.In order to obtain reasonably optimal values of the free parameters in the generalized symmetric fourth-order decomposition scheme,we eliminate the leading error terms to achieve the accuracy of desired order for the thermodynamic property of the harmonic system.Such a strategy leads to an efficient fourth-order decomposition that produces thirdorder accurate thermodynamic properties for general systems.展开更多
Utilizing infrared spectroscopy,we study the charge dynamics of the topological superconductor candidate Sr_(x)Bi_(2)Se_(3).The frequency-dependent reflectivity R(ω)demonstrates metallic feature and the scattering ra...Utilizing infrared spectroscopy,we study the charge dynamics of the topological superconductor candidate Sr_(x)Bi_(2)Se_(3).The frequency-dependent reflectivity R(ω)demonstrates metallic feature and the scattering rate of the free carriers decreases with temperature decreasing.The plasma edge shows a slight blue shift upon cooling,similar to the behavior of Cu_(x)Bi_(2)Se_(3).As the carrier concentration n obtained by Hall resistivity increases slightly with the decreasing temperature,the effective mass is proved to increase as well,which is in contrast with that of Cu_(x)Bi_(2)Se_(3).We also perform the ultrafast pump-probe study on the Sr_(0.2)Bi_(2)Se_(3)compounds.Resembling its parent compound Bi_(2)Se_(3),three distinct relaxation processes are found to contribute to the transient reflectivity.However,the deduced relaxation times are quite different.In addition,the electron-optical-phonon coupling constant is identified to beλ=0.88.展开更多
We conducted a comparative study of the magnetic and transport properties of single-crystalline LaCo_(2)As_(2) and NdCo_(2)As_(2).LaCo_(2)As_(2) is a soft metallic ferromagnet which exhibits purely intrinsic anomalous...We conducted a comparative study of the magnetic and transport properties of single-crystalline LaCo_(2)As_(2) and NdCo_(2)As_(2).LaCo_(2)As_(2) is a soft metallic ferromagnet which exhibits purely intrinsic anomalous Hall effect(AHE) due to Co-3d electrons. With Nd-4f electronic magnetism, ferrimagnetic NdCo_(2)As_(2) manifests pronounced sign reversal and multiple hysteresis loops in temperature-and field-dependent magnetization, Hall resistivity, and magnetoresistance, due to complicated magnetic structural changes. We reveal that the AHE for NdCo_(2)As_(2) is stemming from the Co sub-lattice and deduce its phase diagram which includes magnetic compensation and two meta-magnetic phase transitions. The sensitivity of the Hall effect on the details of the magnetic structures in ferrimagnetic NdCo_(2)As_(2) provides a unique opportunity to explore the magnetic interaction between 4f and 3d electrons and its impact on the electronic structure.展开更多
基金supported by the Science Research Project of Hebei Education Department(Grant No.BJK2024168)the National Natural Science Foundation of China(Grant No.11904076)+1 种基金the Natural Science Foundation of Hebei(Grant No.A2019205313)Science Foundation of Hebei Normal University(Grant No.L2024J02).
文摘Recent advancements in two-dimensional van der Waals moir´e materials have unveiled the captivating landscape of moir´e physics.In twisted bilayer graphene(TBG)at‘magic angles’,strong electronic correlations give rise to a diverse array of exotic physical phenomena,including correlated insulating states,superconductivity,magnetism,topological phases,and the quantum anomalous Hall(QAH)effect.Notably,the QAH effect demonstrates substantial promise for applications in electronic and quantum computing devices with low power consumption.This article focuses on the latest developments surrounding the QAH effect in magic-angle TBG.It provides a comprehensive analysis of magnetism and topology—two crucial factors in engineering the QAH effect within magic-angle TBG.Additionally,it offers a detailed overview of the experimental realization of the QAH effect in moir´e superlattices.Furthermore,this review highlights the underlying mechanisms driving these exotic phases in moir´e materials,contributing to a deeper understanding of strongly interacting quantum systems and facilitating the manipulation of new material properties to achieve novel quantum states.
基金supported by the National Natural Science Foun-dation of China(62301596 and 62288101)Shaanxi Provincial Science and Technology Innovation Team(23-CX-TD-48)+4 种基金the KU Leuven internal funds:the C1 Project(C14/19/083)the Interdisciplinary Network Project(IDN/20/014)the Small Infrastructure Grant(KA/20/019)the Research Foundation of Flanders(FWO)Project(G090017N,G088822N,and V408823N)the Danish National Research Foundation(DNRF165).
文摘Optical singularities are topological defects of electromagnetic fields;they include phase singularity in scalar fields,polarization singularity in vector fields,and three-dimensional(3D)singularities such as optical skyrmions.The exploitation of photonic microstructures to generate and manipulate optical singularities has attracted wide research interest in recent years,with many photonic microstructures having been devised to this end.Accompanying these designs,scattered phenomenological theories have been proposed to expound the working mechanisms behind individual designs.In this work,instead of focusing on a specific type of microstructure,we concentrate on the most common geometric features of these microstructures—namely,symmetries—and revisit the process of generating optical singularities in microstructures from a symmetry viewpoint.By systematically employing the projection operator technique in group theory,we develop a widely applicable theoretical scheme to explore optical singularities in microstructures with rosette(i.e.,rotational and reflection)symmetries.Our scheme agrees well with previously reported works and further reveals that the eigenmodes of a symmetric microstructure can support multiplexed phase singularities in different components,such as out-of-plane,radial,azimuthal,and left-and right-handed circular components.Based on these phase singularities,more complicated optical singularities may be synthesized,including C points,V points,L lines,Néel-and bubble-type optical skyrmions,and optical lattices,to name a few.We demonstrate that the topological invariants associated with optical singularities are protected by the symmetries of the microstructure.Lastly,based on symmetry arguments,we formulate a so-called symmetry matching condition to clarify the excitation of a specific type of optical singularity.Our work establishes a unified theoretical framework to explore optical singularities in photonic microstructures with symmetries,shedding light on the symmetry origin of multidimensional and multiplexed optical singularities and providing a symmetry perspective for exploring many singularity-related effects in optics and photonics.
基金the National Natural Science Foundation of China(No.91753118 and No.21773012)the Fundamental Research Funds for Central Universities。
文摘Two-dimensional Fourier transform(2D FT) spectroscopy is an important technology that developed in recent decades and has many advantages over other ultrafast spectroscopy methods. Although 2D FT spectroscopy provides great opportunities for studying various complex systems, the experimental implementation and theoretical description of 2D FT spectroscopy measurement still face many challenges, which limits their wide application.Recently, the 2D FT spectroscopy reaches maturity due to many new developments which greatly reduces the technical barrier in the experimental implementation of the 2D FT spectrometer. There have been several different approaches developed for the optical design of the 2D FT spectrometer, each with its own advantages and limitations. Thus, a procedure to help an experimentalist to build a 2D FT spectroscopy experimental apparatus is needed.This tutorial review is intending to provide an accessible introduction for a beginner to build a 2D FT spectrometer.
基金Supported by the National Natural Science Foundation of China under Grant No 1167402
文摘Using the linear local induction approximation, we investigate the self-induced motion of a vortex-line that corresponds to the motion of a particle in quantum mechanics. Provided Kelvin waves, the effective Schr?dinger equation, physical quantity operators, and the corresponding path-integral formula can be obtained. In particular,the effective Planck constant defined by parameters of vortex-line motion shows the mathematical relation between the two fields. The vortexline–particle mapping may help in understanding particle motion in quantum mechanics.
基金supported by Beijing Natural Science Foundation(L172028)the National Natural Science Foundation of China(No.21773012 and No.91753118)+1 种基金the Recruitment Program of Global Youth Expertsthe Fundamental Research Funds for Central Universities
文摘Tryptophan derivatives have long been used as site-specific biological probes. 4-Cyanotrypto- phan emits in the visible region and is the smallest blue fluorescent amino acid probe for bio- logical applications. Other indole or tryptophan analogs may emit at even longer wavelengths than 4-cyanotryptophan. We performed FTIR, UV-Vis, and steady-state and time-resolved fluorescence spectroscopy on six ester-derivatized indoles in different solvents. Methyl indole- 4-carboxylate emits at 450 nrn with a long fluorescence lifetirne, and is a promising candidate for a fluorescent probe. The ester-derivatized indoles could be used as spectroscopic probes to study local protein environments. Our measurements provide a guide for choosing esterderivatized indoles to use in practice and data for computational modeling of the effect of substitution on the electronic transitions of indole.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.2243300003)the National Natural Science Foundation of China(Grant No.12074041)the Fundamental Research Program of Shanxi Province,China(Grant No.202203021222228).The calculations were carried out with high performance computing cluster of Beijing Normal University in Zhuhai.
文摘We design two new layered indium halide compounds LaOInF_(2)and LaOInCl_(2)by means of first-principles calculations and evolutionary crystal structure prediction.We find both compounds crystallize in a tetragonal structure with P4/nmm space group and have indirect band gaps of 2.58 eV and 3.21 eV,respectively.By substituting O with F,both of them become metallic and superconducting at low temperature.The F-doping leads to strong electron-phonon coupling in the low-energy acoustic phonon modes which is mainly responsible for the induced superconductivity.The total electron-phonon coupling strength are 1.86 and 1.48,while the superconducting transition temperature(T_(c))are about 7.2 K and 6.5 K with 10%and 5%F doping for LaOInF_(2)and LaOInCl_(2),respectively.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFA1400400)the Fundamental Research Funds for the Central Universities,and the National Natural Science Foundation of China(Grant Nos.12174029 and 11922402).
文摘Uniaxial strain is a powerful tuning parameter that can control symmetry and anisotropic electronic properties in iron-based superconductors.However,accurately characterizing anisotropic strain can be challenging and complex.Here,we utilize a cryogenic optical system equipped with a high-spatial-resolution microscope to characterize surface strains in iron-based superconductors using the digital image correlation method.Compared with other methods such as high-resolution x-ray diffraction,strain gauge,and capacitive sensor,digital image correlation offers a non-contact full-field measurement approach,acting as an optical virtual strain gauge that provides high spatial resolution.The results measured on detwinned BaFe_(2)As_(2)are quantitatively consistent with the distortion measured by x-ray diffraction and neutron Larmor diffraction.These findings highlight the potential of cryogenic digital image correlation as an effective and accessible tool for probing the isotropic and anisotropic strains,facilitating applications of uniaxial strain tuning in research of quantum materials.
基金Beijing Normal University was supported by the Fundamental Research Funds for the Central Universitiesthe National Key Projects for Research and Development of China(No.2021YFA1400400)+1 种基金the National Natural Science Foundation of China(Grant Nos.12174029 and 11922402)the neutron beamtimes from J-PARC(Proposal No.2019A0002)。
文摘Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high-Tc superconductors.In iron-based superconductors,spin excitations at low energy range,especially the spin-resonance mode at ER~5kBTc,are important for understanding the superconductivity.Here,we use inelastic neutron scattering(INS)to investigate the symmetry and in-plane wave-vector dependence of low-energy spin excitations in uniaxial-strain detwinned Fe Se.The low-energy spin excitations(E<10 meV)appear mainly at Q=(±1,0)in the superconducting state(T9K)and the nematic state(T90 K),confirming the constant C_(2) rotational symmetry and ruling out the C_(4) mode at E≈3 meV reported in a prior INS study.Moreover,our results reveal an isotropic spin resonance in the superconducting state,which is consistent with the s±wave pairing symmetry.At slightly higher energy,low-energy spin excitations become highly anisotropic.The full width at half maximum of spin excitations is elongated along the transverse direction.The Q-space isotropic spin resonance and highly anisotropic low-energy spin excitations could arise from dyz intra-orbital selective Fermi surface nesting between the hole pocket aroundΓpoint and the electron pockets centered at MX point.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.12074023,12304053,and 12174018)the Large Scientific Facility Open Subject of Songshan Lake(Dongguan,Guangdong)the Fundamental Research Funds for the Central Universities in China。
文摘Determination of the magnetic structure and confirmation of the presence or absence of inversion(P)and time reversal(Τ)symmetry is imperative for correctly understanding the topological magnetic materials.Here highquality single crystals of the layered manganese pnictide CaMnSb_(2)are synthesized using the self-flux method.
基金supported by the National Natural Science Foundation of China(52303239,51933001)the Natural Science Foundation of Shandong Province(ZR2022QB141,2023HWYQ-087)。
文摘Understanding the effect of intermolecular interaction on the growth dynamic of active layers is critical for advancing organic solar cells(OSCs).However,the diverse structure of donors and acceptors makes the research challenging.Additives with customizable structures and properties could simplify this complexity.Herein,we meticulously tailor two additives of 3,4-ethylenedioxythiophene(EDOT)and 2,5-dibromo-3,4-ethylenedioxythiophene(DBEDOT),possessing distinct intermolecular interaction features to elaborate the inherent relationship.It is found that varied interaction strengths can alter film formation processes.The enhanced intermolecular interaction between the DBEDOT and non-fullerene acceptor BTP-e C9-4F results in pre-aggregation and longer crystallization duration of BTP-e C9-4F,facilitating the formation of films with compact molecular packing and decent phase separation.Thus,exciton dissociation and charge transport become more efficient.Finally,devices processed with DBEDOT exhibit a remarkable power conversion efficiency of 19.35%in small-area OSCs and 14.11%in bladecoated 5 cm×5 cm organic solar mini-modules.Especially,OSCs can maintain 80%of their initial efficiency after continuous annealing at 85℃for over 2,100 h.
基金Supported by the National Natural Science Foundation of China(Grant Nos.11674026 and 11974053)。
文摘Breakdown of bulk-boundary correspondence in non-Hermitian(NH)topological systems with generalized inversion symmetries is a controversial issue.The non-Bloch topological invariants determine the existence of edge states,but fail to describe the number and distribution of defective edge states in non-Hermitian topological systems.The state-dependent topological invariants,instead of a global topological invariant,are developed to accurately characterize the bulk-boundary correspondence of the NH systems,which is very different from their Hermitian counterparts.At the same time,we obtain the accurate phase diagram of the one-dimensional non-Hermitian Su–Schrieffer–Heeger model with a generalized inversion symmetry from the state-dependent topological invariants.Therefore,these results will be helpful for understanding the exotic topological properties of various non-Hermitian systems.
基金National Natural Science Foundation of China,Grant/Award Numbers:52173174,51933001,22109080Natural Science Foundation of Shandong Province,Grant/Award Number:ZR2022YQ45Taishan Scholars Program,Grant/Award Numbers:tstp20221121,tsqnz20221134。
文摘The side-chain has a significant influence on the optical properties and aggregation behaviors of the organic small molecule acceptors,which becomes an important strategy to optimize the photovoltaic performance of organic solar cells.In this work,we designed and synthesized three brand-new nonfused ring electron acceptors(NFREAs)OC4-4Cl-Ph,OC4-4Cl-Th,and OC4-4Cl-C8 with hexylbenzene,hexylthiophene,and octyl side chains on theπ-bridge units.Compared with OC4-4Cl-Ph and OC4-4Cl-Th,OC4-4Cl-C8 with linear alkyl side chain has more red-shift absorption,which is conducive to obtaining higher short-circuit current density.Additionally,the OC4-4Cl-C8 film exhibits a longer exciton diffusion distance,and the D18:OC4-4Cl-C8 blend film displays faster hole transfer,weaker bimolecular recombination,and more efficient exciton transport.Furthermore,The D18:OC4-4Cl-C8 blend films may effectively form interpenetrating networks that resemble nanofibrils,which can facilitate exciton dissociation and charge transport.Finally,OC4-4Cl-C8-based devices can be created a marvellously power conversion efficiency(PCE)of 16.56%,which is much higher than OC4-4Cl-Ph(12.29%)-and OC4-4Cl-Th-based(11.00%)ones,being the highest PCE among the NFREA based binary devices.All in all,we have validated that side-chain engineering is an efficient way to achieve high-performance NFREAs.
基金Project supported by the Fundamental Research Funds for the Central Universities,China(Grant No.2014JJCB27).
文摘The in-plane magnetotransport of detwinned EuFe2As2 single crystal has been investigated.In the antiferromagnetic phase of Eu^2+spins,very different magnetoresistance results are observed upon the change of the external magnetic field direction and the current direction.This could be attributed to the tunable orientation of the Eu^2+spins under magnetic field.Electron scattering by spin fluctuation,superzone boundary effect,and cyclotron motion of charge carriers are used to interpret the observed anomalous magnetoresistance which is measured by using a current along a direction.The remarkable features of magnetoresistance suggest that itinerant electrons strongly couple with the spin configuration of Eu^2+,which has a huge influence on the transport properties of EuFe2As2.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFA1405100)the Beijing Natural Science Foundation Key Program(Grant No.Z190007)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB44000000 and XDB28000000)the National Natural Science Foundation of China(Grant Nos.12241405,11734004,and 12174028)。
文摘The emergent van der Waals magnetic material is a promising component for spintronic devices with novel functionalities.Here,we report a transition of negative-to-positive magnetoresistance in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)van der Waals all-magnetic tunnel junctions with increasing the applied bias voltage.A negative magnetoresistance is observed first in Fe_(3)GeTe_(2)/Cr_(2)Ge_(2)Te_(6)/Fe_(3)GeTe_(2)tunnel junctions,where the resistance with antiparallel aligned magnetization of two Fe_(3)GeTe_(2)electrodes is lower than that with parallel alignment,which is due to the opposite spin polarizations of two Fe_(3)GeTe_(2)electrodes.With the bias voltage increasing,the spin polarization of the biased Fe_(3)GeTe_(2)electrode is changed so that the spin orientations of two Fe_(3)GeTe_(2)electrodes are the same.Our experimental observations are supported by the calculated spin-dependent density of states for Fe_(3)GeTe_(2)electrodes under a finite bias.The significantly bias voltage-dependent spin transport properties in van der Waals magnetic tunnel junctions open a promising route for designing electrical controllable spintronic devices based on van der Waals magnets.
文摘The electronic properties of van der Waals(vd W) structures can be substantially modified by the moiré superlattice potential, which strongly depends on the twist angle among the compounds. In twisted bilayer graphene(TBG), two lowenergy Van Hove singularities(VHSs) move closer with decreasing twist angles and finally become highly non-dispersive flat bands at the magic angle(~1.1°). When the Fermi level lies within the flat bands of the TBG near the magic angle,Coulomb interaction is supposed to exceed the kinetic energy of the electrons, which can drive the system into various strongly correlated phases. Moreover, the strongly correlated states of flat bands are also realized in other graphene-based vd W structures with an interlayer twist. In this article, we mainly review the recent scanning tunneling microscopy(STM)advances on the strongly correlated physics of the magic-angle TBG(MATBG) and the small-angle twisted multilayer graphene. Lastly we will give out a perspective of this field.
基金financial supported by the National Natural Science Foundation of China(Grant Nos.92163206 and 61725107)the National Key Research and Development Program of China(Grant No.2020YFA0308800)+1 种基金Beijing Natural Science Foundation(Grant No.Z190006)China Postdoctoral Science Foundation(Grant No.2021M700407)。
文摘Electrons in graphene have fourfold spin and valley degeneracies owing to the unique bipartite honeycomb lattice and an extremely weak spin-orbit coupling,which can support a series of broken symmetry states.Atomic-scale defects in graphene are expected to lift these degenerate degrees of freedom at the nanoscale,and hence,lead to rich quantum states,highlighting promising directions for spintronics and valleytronics.In this article,we mainly review the recent scanning tunneling microscopy(STM)advances on the spin and/or valley polarized states induced by an individual atomicscale defect in graphene,including a single-carbon vacancy,a nitrogen-atom dopant,and a hydrogen-atom chemisorption.Lastly,we give a perspective in this field.
基金supported by the National Key Projects for Research and Development of China (Grant No.2021YFA1400400)the National Natural Science Foundation of China (Grant Nos.12174029 and 11922402)+3 种基金supported by the National Key Research and Development Program of China (Grant No.2022YFA1402200)the Pioneer and Leading Goose Research and Development Program of Zhejiang Province,China (Grant No.2022SDX-HDX0005)the Key Research and Development Program of Zhejiang Province,China (Grant No.2021C01002)the National Natural Science Foundation of China (Grant No.12274363)。
文摘The kagome superconductor CsV_(3)Sb_(5) with exotic electronic properties has attracted substantial research interest,and the interplay between the superconductivity and the charge-density wave is crucial for understanding its unusual electronic ground state.In this work,we performed resistivity and AC magnetic susceptibility measurements on CsV_(3)Sb_(5) single crystals uniaxially-strained along[100]and[110]directions.We find that the uniaxial-strain tuning effect of T_(c)(dT_(c)/dε)and T_(CDW)(dT_(CDW)/dε)are almost identical along these distinct high-symmetry directions.These findings suggest the in-plane uniaxial-strain-tuning of T_(c) and T_(CDW)in CsV_(3)Sb_(5) are dominated by associated c-axis strain,whereas the response to purely in-plane strains is likely small.
基金supported by the National Natural Science Foundation of China(No.21961142017,No.22073009 and No.21421003)the Ministry of Science and Technology of China(No.2017YFA0204901)。
文摘The imaginary time path integral formalism offers a powerful numerical tool for simulating thermodynamic properties of realistic systems.We show that,when second-order and fourth-order decompositions are employed,they share a remarkable unified analytic form for the partition function of the harmonic oscillator.We are then able to obtain the expression of the thermodynamic property and the leading error terms as well.In order to obtain reasonably optimal values of the free parameters in the generalized symmetric fourth-order decomposition scheme,we eliminate the leading error terms to achieve the accuracy of desired order for the thermodynamic property of the harmonic system.Such a strategy leads to an efficient fourth-order decomposition that produces thirdorder accurate thermodynamic properties for general systems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074042 and 11704033)the National Key Research and Development Program of China(Grant Nos.2021YFA1400400 and 2016YFA0302300)the Fundamental Research Funds for the Central Universities。
文摘Utilizing infrared spectroscopy,we study the charge dynamics of the topological superconductor candidate Sr_(x)Bi_(2)Se_(3).The frequency-dependent reflectivity R(ω)demonstrates metallic feature and the scattering rate of the free carriers decreases with temperature decreasing.The plasma edge shows a slight blue shift upon cooling,similar to the behavior of Cu_(x)Bi_(2)Se_(3).As the carrier concentration n obtained by Hall resistivity increases slightly with the decreasing temperature,the effective mass is proved to increase as well,which is in contrast with that of Cu_(x)Bi_(2)Se_(3).We also perform the ultrafast pump-probe study on the Sr_(0.2)Bi_(2)Se_(3)compounds.Resembling its parent compound Bi_(2)Se_(3),three distinct relaxation processes are found to contribute to the transient reflectivity.However,the deduced relaxation times are quite different.In addition,the electron-optical-phonon coupling constant is identified to beλ=0.88.
基金Project supported by the National Key Research and Development Program of China(Grant No.2018YFB1502502)the National Natural Science Foundation of China(Grant Nos.12141002 and 12225401)+6 种基金the Fund from Foshan Xianhu Laboratory of the Advanced Energy Science and Technology Guangdong Laboratorysupported by the Interdisciplinary Program of Wuhan National High Magnetic Field Center(Grant No.WHMFC202123)Huazhong University of Science and Technologysupported by the National Natural Science Foundation of China(Grant Nos.12074041 and 11674030)the Foundation of the National Key Laboratory of Shock Wave and Detonation Physics(Grant No.6142A03191005)the National Key Research and Development Program of China(Grant No.2016YFA0302300)the startup funding of Beijing Normal University。
文摘We conducted a comparative study of the magnetic and transport properties of single-crystalline LaCo_(2)As_(2) and NdCo_(2)As_(2).LaCo_(2)As_(2) is a soft metallic ferromagnet which exhibits purely intrinsic anomalous Hall effect(AHE) due to Co-3d electrons. With Nd-4f electronic magnetism, ferrimagnetic NdCo_(2)As_(2) manifests pronounced sign reversal and multiple hysteresis loops in temperature-and field-dependent magnetization, Hall resistivity, and magnetoresistance, due to complicated magnetic structural changes. We reveal that the AHE for NdCo_(2)As_(2) is stemming from the Co sub-lattice and deduce its phase diagram which includes magnetic compensation and two meta-magnetic phase transitions. The sensitivity of the Hall effect on the details of the magnetic structures in ferrimagnetic NdCo_(2)As_(2) provides a unique opportunity to explore the magnetic interaction between 4f and 3d electrons and its impact on the electronic structure.
