As an essential concept to understand the world,whether the real values(or physical realities)of observables are suitable to physical systems beyond the classic has been debated for many decades.Although standard nogo...As an essential concept to understand the world,whether the real values(or physical realities)of observables are suitable to physical systems beyond the classic has been debated for many decades.Although standard nogo results based on Bell inequalities have ruled out the joint reality of incompatible quantum observables,the possibility of giving simple yet strong arguments to rule out joint reality in any physical system(not necessarily quantum)with weaker assumptions and less observables has been explored and proposed recently.Here,we perform a device-independent experiment on a two-qubit superconducting system to show that the joint reality of two observables is incompatible with locality under the weaker assumption of the reality of observables in a single space-time region(or single qubit).Our results clearly show the violation of certain inequalities derived from both linear and nonlinear criteria.In addition,we study the robustness of the linear and nonlinear criterion against the effect of systematic decoherence.Our demonstration opens up the possibility of delineating classical and non-classical boundaries with simpler nontrivial quantum system.展开更多
Motivated by recent experimental progress on the quasi-one-dimensional quantum magnet Ni Nb2O6, we study the spin dynamics of an S = 1 ferromagnetic Heisenberg chain with single-ion anisotropy by using a semiclassical...Motivated by recent experimental progress on the quasi-one-dimensional quantum magnet Ni Nb2O6, we study the spin dynamics of an S = 1 ferromagnetic Heisenberg chain with single-ion anisotropy by using a semiclassical molecular dynamics approach. This system undergoes a quantum phase transition from a ferromagnetic to a paramagnetic state under a transverse magnetic field, and the magnetic response reflecting this transition is well described by our semiclassical method.We show that at low temperature the transverse component of the dynamical structure factor depicts clearly the magnon dispersion, and the longitudinal component exhibits two continua associated with single-and two-magnon excitations,respectively. These spin excitation spectra show interesting temperature dependence as effects of magnon interactions. Our findings shed light on the experimental detection of spin excitations in a large class of quasi-one-dimensional magnets.展开更多
We study superradiant phase transitions in a hybrid system of a two-dimensional Bose–Einstein condensate of atoms and two cavities arranged with a tilt angle.By adjusting the loss rate of cavities,we map out the phas...We study superradiant phase transitions in a hybrid system of a two-dimensional Bose–Einstein condensate of atoms and two cavities arranged with a tilt angle.By adjusting the loss rate of cavities,we map out the phase diagram of steady states within a mean field framework.It is found that when the loss rates of the two cavities are different,superradiant transitions may not occur at the same time in the two cavities.A first-order phase transition is observed between the states with only one cavity in superradiance and both in superradiance.In the case that both cavities are superradiant,a net photon current is observed flowing from the cavity with small decay rate to the one with large decay rate.The photon current shows a non-monotonic dependence on the loss rate difference,owing to the competition of photon number difference and cavity field phase difference.Our findings can be realized and detected in experiments.展开更多
By using first-principles electronic structure calculations,we propose a two-dimensional ferromagnetic semiconductor Li_(2)NiSe_(2)with a Curie temperature above 200 K.The structure of monolayer Li_(2)NiSe_(2)is dynam...By using first-principles electronic structure calculations,we propose a two-dimensional ferromagnetic semiconductor Li_(2)NiSe_(2)with a Curie temperature above 200 K.The structure of monolayer Li_(2)NiSe_(2)is dynamically stable,which is derived from the synthesized prototype compound Li_(2)Ni O_(2)and can be denoted as Li-decorated 1T-type NiSe_(2).The Ni–Se–Ni ferromagnetic superexchange dominates the magnetic couplings between the Ni atoms,which can be understood in the frame of the Goodenough–Kanamori–Anderson(GKA)rules.Our systematic study of monolayer Li_(2)NiSe_(2)enables its promising applications in spintronics and suggests a new choice to design two-dimensional ferromagnetic semiconductors.展开更多
The electronic evolution of Mott insulators into exotic correlated phases remains puzzling,because of electron interaction and inhomogeneity.Introduction of individual imperfections in Mott insulators could help captu...The electronic evolution of Mott insulators into exotic correlated phases remains puzzling,because of electron interaction and inhomogeneity.Introduction of individual imperfections in Mott insulators could help capture the main mechanism and serve as a basis to understand the evolution.Here we utilize scanning tunneling microscopy to probe the atomic scale electronic structure of the spin-orbit-coupling assisted Mott insulator Sr_(3)Ir_(2)O_(7).It is found that the tunneling spectra exhibit a homogeneous Mott gap in defect-free regions,but near the oxygen vacancy in the rotated Ir O_(2)plane the local Mott gap size is significantly enhanced.We attribute the enhanced gap to the locally reduced hopping integral between the 5d electrons of neighboring Ir sites via the bridging planar oxygen p orbitals.Such bridging defects have a dramatic influence on local bandwidth,thus provide a new way to manipulate the strength of Mottness in a Mott insulator.展开更多
The security of information is not assured over extended periods,especially with the rapid advancement of quantum computers.To address this challenge,quantum cryptography,rooted in quantum physics,offers comprehensive...The security of information is not assured over extended periods,especially with the rapid advancement of quantum computers.To address this challenge,quantum cryptography,rooted in quantum physics,offers comprehensive toolkits for key distribution[1],secret sharing[2],digital signatures[3]and other cryptographic tasks[4]with information-theoretical security.The feasibility of quantum cryptography,particularly quantum key distribution(QKD)。展开更多
By using first-principles electronic structure calculations, we have studied the magnetic interactions in a proposed BaZn2P2-based diluted magnetic semiconductor(DMS). For a typical compound Ba(Zn(0.944)Mn(0.05...By using first-principles electronic structure calculations, we have studied the magnetic interactions in a proposed BaZn2P2-based diluted magnetic semiconductor(DMS). For a typical compound Ba(Zn(0.944)Mn(0.056))2P2 with only spin doping, due to the superexchange interaction between Mn atoms and the lack of itinerant carriers, the short-range antiferromagnetic coupling dominates. Partially substituting K atoms for Ba atoms, which introduces itinerant hole carriers into the p orbitals of P atoms so as to link distant Mn moments with the spin-polarized hole carriers via the p–d hybridization between P and Mn atoms, is very crucial for the appearance of ferromagnetism in the compound. Furthermore, applying hydrostatic pressure first enhances and then decreases the ferromagnetic coupling in(Ba0.75 K0.25)(Zn(0.944)Mn(0.056))2P2 at a turning point around 15 GPa, which results from the combined effects of the pressure-induced variations of electron delocalization and p–d hybridization. Compared with the BaZn2 As2-based DMS, the substitution of P for As can modulate the magnetic coupling effectively. Both the results for BaZn2 P2-based and BaZn2As2-based DMSs demonstrate that the robust antiferromagnetic(AFM) coupling between the nearest Mn–Mn pairs bridged by anions is harmful to improving the performance of these Ⅱ–Ⅱ–Ⅴ based DMS materials.展开更多
We train a neural network to identify impurities in the experimental images obtained by the scanning tunneling microscope(STM)measurements.The neural network is first trained with a large number of simulated data and ...We train a neural network to identify impurities in the experimental images obtained by the scanning tunneling microscope(STM)measurements.The neural network is first trained with a large number of simulated data and then the trained neural network is applied to identify a set of experimental images taken at different voltages.We use the convolutional neural network to extract features from the images and also implement the attention mechanism to capture the correlations between images taken at different voltages.We note that the simulated data can capture the universal Friedel oscillation but cannot properly describe the non-universal physics short-range physics nearby an impurity,as well as noises in the experimental data.And we emphasize that the key of this approach is to properly deal with these differences between simulated data and experimental data.Here we show that even by including uncorrelated white noises in the simulated data,the performance of the neural network on experimental data can be significantly improved.To prevent the neural network from learning unphysical short-range physics,we also develop another method to evaluate the confidence of the neural network prediction on experimental data and to add this confidence measure into the loss function.We show that adding such an extra loss function can also improve the performance on experimental data.Our research can inspire future similar applications of machine learning on experimental data analysis.展开更多
Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid(QSL), and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular...Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid(QSL), and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular lattice spin liquid candidate YbMgGaO_4 stimulated an increasing attention on the rare-earth-based frustrated magnets with strong spin-orbit coupling. Here we report the synthesis and characterization of a large family of rare-earth chalcogenides AReCh_2(A = alkali or monovalent ions, Re = rare earth, Ch = O,S,Se). The family compounds share the same structure(R3 m) as YbMgGaO_4,and antiferromagnetically coupled rare-earth ions form perfect triangular layers that are well separated along the c-axis. Specific heat and magnetic susceptibility measurements on NaYbO_2,NaYbS_2 and NaYbSe_2 single crystals and polycrystals, reveal no structural or magnetic transition down to 50 mK. The family, having the simplest structure and chemical formula among the known QSL candidates, removes the issue on possible exchange disorders in YbMgGaO_4. More excitingly, the rich diversity of the family members allows tunable charge gaps, variable exchange coupling, and many other advantages.This makes the family an ideal platform for fundamental research of QSLs and its promising applications.展开更多
We report the detailed physical properties of quaternary compound Ba2BiFeS5 with the key structural ingredient of isolated FeS4 tetrahedra.Magnetization and heat capacity measurements clearly indicate that Ba2BiFeS5 h...We report the detailed physical properties of quaternary compound Ba2BiFeS5 with the key structural ingredient of isolated FeS4 tetrahedra.Magnetization and heat capacity measurements clearly indicate that Ba2BiFeS5 has a paramagnetic to antiferromagnetic transition at about 30 K.The calculated magnetic entropy above ordering temperature is much smaller than theoretical value for high-spin Fe^3+ion with S=5/2,implying the possible short-range antiferromagnetic fluctuation in Ba2BiFeS5.展开更多
Growth of high-quality single crystals is of great significance for research of condensed matter physics. The exploration of suitable growing conditions for single crystals is expensive and time-consuming, especially ...Growth of high-quality single crystals is of great significance for research of condensed matter physics. The exploration of suitable growing conditions for single crystals is expensive and time-consuming, especially for ternary compounds because of the lack of ternary phase diagram. Here we use machine learning(ML) trained on our experimental data to predict and instruct the growth. Four kinds of ML methods, including support vector machine(SVM), decision tree, random forest and gradient boosting decision tree, are adopted. The SVM method is relatively stable and works well, with an accuracy of 81% in predicting experimental results. By comparison,the accuracy of laboratory reaches 36%. The decision tree model is also used to reveal which features will take critical roles in growing processes.展开更多
We study the critical scaling and dynamical signatures of fractionalized excitations at two different deconfined quantum critical points(DQCPs)in an S=1/2 spin chain using the time evolution of infinite matrix product...We study the critical scaling and dynamical signatures of fractionalized excitations at two different deconfined quantum critical points(DQCPs)in an S=1/2 spin chain using the time evolution of infinite matrix product states.The scaling of the correlation functions and the dispersion of the conserved current correlations explicitly show the emergence of enhanced continuous symmetries at these DQCPs.The dynamical structure factors in several different channels reveal the development of deconfined fractionalized excitations at the DQCPs.Furthermore,we find an effective spin-charge separation at the DQCP between the ferromagnetic(FM)and valence bond solid(VBS)phases,and identify two continua associated with different types of fractionalized excitations at the DQCP between the X-direction and Z-direction FM phases.Our findings not only provide direct evidence for the DQCP in one dimension but also shed light on exploring the DQCP in higher dimensions.展开更多
Motivated by the growing interest in the novel quantum phases in materials with strong electron correlations and spin–orbit coupling, we study the interplay among the spin–orbit coupling, Kondo interaction, and magn...Motivated by the growing interest in the novel quantum phases in materials with strong electron correlations and spin–orbit coupling, we study the interplay among the spin–orbit coupling, Kondo interaction, and magnetic frustration of a Kondo lattice model on a two-dimensional honeycomb lattice.We calculate the renormalized electronic structure and correlation functions at the saddle point based on a fermionic representation of the spin operators.We find a global phase diagram of the model at half-filling, which contains a variety of phases due to the competing interactions.In addition to a Kondo insulator, there is a topological insulator with valence bond solid correlations in the spin sector, and two antiferromagnetic phases.Due to the competition between the spin–orbit coupling and Kondo interaction, the direction of the magnetic moments in the antiferromagnetic phases can be either within or perpendicular to the lattice plane.The latter antiferromagnetic state is topologically nontrivial for moderate and strong spin–orbit couplings.展开更多
We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7that exhibits stronger two-dimensional character than the prototypical heavy fermion system ...We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7that exhibits stronger two-dimensional character than the prototypical heavy fermion system CeCoIn5.Multiple Fermi surface sheets and a complex band structure are clearly resolved. We have also performed detailed band structure calculations on CePt2In7. The good agreement found between our measurements and the calculations suggests that the band renormalization effect is rather weak in CePt2In7. A comparison of the common features of the electronic structure of CePt2In7and CeCoIn5indicates that CeCoIn5shows a much stronger band renormalization effect than CePt2In7. These results provide new information for understanding the heavy fermion behaviors and unconventional superconductivity in Ce-based heavy fermion systems.展开更多
The discovery of high temperature superconductivity in FeSe films on SrTiO3 substrate has inspired great experimen- tal and theoretical interests. First-principles density functional theory calculations, which have pl...The discovery of high temperature superconductivity in FeSe films on SrTiO3 substrate has inspired great experimen- tal and theoretical interests. First-principles density functional theory calculations, which have played an important role in the study of bulk iron-based superconductors, also participate in the investigation of interfacial superconductivity. In this article, we review the calculation results on the electronic and magnetic structures of FeSe epitaxial films, emphasiz- ing on the interplay between different degrees of freedom, such as charge, spin, and lattice vibrations. Furthermore, the comparison between FeSe monolayer and bilayer films on SrTiO3 is discussed.展开更多
In quasi-one-dimensional(q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase tr...In quasi-one-dimensional(q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic(AFM) compound YbAlO3, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations,and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave(LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.展开更多
We present the experiment observation of a giant topological Hall effect(THE)in a frustrated kagome bilayer magnet Fe3Sn2.The negative topologically Hall resistivity appears when the field is below 1.3 T and it increa...We present the experiment observation of a giant topological Hall effect(THE)in a frustrated kagome bilayer magnet Fe3Sn2.The negative topologically Hall resistivity appears when the field is below 1.3 T and it increases with increasing temperature up to 300 K.Its maximum absolute value reaches^2.01μΩ·cm at 300 K and 0.76 T.The origins of the observed giant THE can be attributed to the coexistence of the field-induced skyrmion state and the non-collinear spin configuration,possibly related to the magnetic frustration interaction in Fe3Sn2.展开更多
Recently rare-earth chalcogenides have been revealed as a family of quantum spin liquid(QSL)candidates hosting a large number of members.In this paper we report the crystal growth and magnetic measurements of KErTe_(2...Recently rare-earth chalcogenides have been revealed as a family of quantum spin liquid(QSL)candidates hosting a large number of members.In this paper we report the crystal growth and magnetic measurements of KErTe_(2),which is the first member of telluride in the family.Compared to its cousins of oxides,sulfides and selenides,KErTe_(2) retains the high symmetry of R3m and Er3+ions still sit on a perfect triangular lattice.The separation between adjacent magnetic layers is expectedly increased,which further enhances the two dimensionality of the spin system.Specific heat and magnetic susceptibility measurements on KErTe_(2) single crystals reveal no structural and magnetic transition down to 1.8 K.Most interestingly,the absorption spectrum shows that the charge gap of KErTe_(2) is roughly 0.93±0.35 eV,which is the smallest among all the reported members in the family.This immediately invokes the interest towards metallization even superconductivity using the compound.展开更多
The generation of highly polarized high-energy brilliantγ-rays via laser–plasma interaction is investigated in the quantum radiation-reaction regime.We employ a quantum electrodynamics particle-in-cell code to descr...The generation of highly polarized high-energy brilliantγ-rays via laser–plasma interaction is investigated in the quantum radiation-reaction regime.We employ a quantum electrodynamics particle-in-cell code to describe spin-resolved electron dynamics semiclassically and photon emission and polarization quantum mechanically in the local constant field approximation.As an ultrastrong linearly polarized(LP)laser pulse irradiates a near-critical-density(NCD)plasma followed by an ultrathin planar aluminum target,the electrons in the NCD plasma are first accelerated by the driving laser to ultrarelativistic energies and then collide head-on with the laser pulse reflected by the aluminum target,emitting brilliant LPγ-rays via nonlinear Compton scattering with an average polarization of about 70%and energy up to hundreds of MeV.Suchγ-rays can be produced with currently achievable laser facilities and will find various applications in high-energy physics and laboratory astrophysics.展开更多
We have synthesized and investigated physical properties of two new quaternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals, which are isostructural to Tb2NiAl4Ge2 and Er2CoAl4Ge2. The most important structural f...We have synthesized and investigated physical properties of two new quaternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals, which are isostructural to Tb2NiAl4Ge2 and Er2CoAl4Ge2. The most important structural feature of these materials is the anti-CaF2-type CoAl4T2 slabs. These materials show metallic behavior below 300 K and there is a long-range antiferromagnetic (AFM) transition appearing at 20 and 27 K for GdCoAl4Ge2 and Gd2CoAl4Si2, respectively. Resistivity and heat capacity measurements also confirm these bulk AFM transitions. Further analysis indicates that this long-range antiferromagnetism should result from the magnetic interaction between local moments of Gd^3+ ions.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12074427,12074428,12204535,and 92265208)the National Key R&D Program of China(Grant Nos.2018YFA0306501 and 2022YFA1405301).
文摘As an essential concept to understand the world,whether the real values(or physical realities)of observables are suitable to physical systems beyond the classic has been debated for many decades.Although standard nogo results based on Bell inequalities have ruled out the joint reality of incompatible quantum observables,the possibility of giving simple yet strong arguments to rule out joint reality in any physical system(not necessarily quantum)with weaker assumptions and less observables has been explored and proposed recently.Here,we perform a device-independent experiment on a two-qubit superconducting system to show that the joint reality of two observables is incompatible with locality under the weaker assumption of the reality of observables in a single space-time region(or single qubit).Our results clearly show the violation of certain inequalities derived from both linear and nonlinear criteria.In addition,we study the robustness of the linear and nonlinear criterion against the effect of systematic decoherence.Our demonstration opens up the possibility of delineating classical and non-classical boundaries with simpler nontrivial quantum system.
基金Project supported by the National Key R&D Program of China (Grant No. 2023YFA1406500)the National Natural Science Foundation of China (Grant Nos. 12334008, 12174441,12134020, and 12374156)。
文摘Motivated by recent experimental progress on the quasi-one-dimensional quantum magnet Ni Nb2O6, we study the spin dynamics of an S = 1 ferromagnetic Heisenberg chain with single-ion anisotropy by using a semiclassical molecular dynamics approach. This system undergoes a quantum phase transition from a ferromagnetic to a paramagnetic state under a transverse magnetic field, and the magnetic response reflecting this transition is well described by our semiclassical method.We show that at low temperature the transverse component of the dynamical structure factor depicts clearly the magnon dispersion, and the longitudinal component exhibits two continua associated with single-and two-magnon excitations,respectively. These spin excitation spectra show interesting temperature dependence as effects of magnon interactions. Our findings shed light on the experimental detection of spin excitations in a large class of quasi-one-dimensional magnets.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1405300)the National Natural Science Foundation of China(Grant Nos.11734010,12074428,12174358,and 92265208)NSAF(Grant No.U2330401)。
文摘We study superradiant phase transitions in a hybrid system of a two-dimensional Bose–Einstein condensate of atoms and two cavities arranged with a tilt angle.By adjusting the loss rate of cavities,we map out the phase diagram of steady states within a mean field framework.It is found that when the loss rates of the two cavities are different,superradiant transitions may not occur at the same time in the two cavities.A first-order phase transition is observed between the states with only one cavity in superradiance and both in superradiance.In the case that both cavities are superradiant,a net photon current is observed flowing from the cavity with small decay rate to the one with large decay rate.The photon current shows a non-monotonic dependence on the loss rate difference,owing to the competition of photon number difference and cavity field phase difference.Our findings can be realized and detected in experiments.
基金the National Key Research and Development Program of China(Grant No.2019YFA0308603)the National Natural Science Foundation of China(Grant No.11934020).
文摘By using first-principles electronic structure calculations,we propose a two-dimensional ferromagnetic semiconductor Li_(2)NiSe_(2)with a Curie temperature above 200 K.The structure of monolayer Li_(2)NiSe_(2)is dynamically stable,which is derived from the synthesized prototype compound Li_(2)Ni O_(2)and can be denoted as Li-decorated 1T-type NiSe_(2).The Ni–Se–Ni ferromagnetic superexchange dominates the magnetic couplings between the Ni atoms,which can be understood in the frame of the Goodenough–Kanamori–Anderson(GKA)rules.Our systematic study of monolayer Li_(2)NiSe_(2)enables its promising applications in spintronics and suggests a new choice to design two-dimensional ferromagnetic semiconductors.
基金the National Key R&D Program of China(Grant No.2017YFA0302900)the Basic Science Center Project of National Natural Science Foundation of China(Grant No.51788104)+4 种基金supported in part by the Beijing Advanced Innovation Center for Future Chip(ICFC)Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physicssupported by the National Natural Science Foundation of China(Grant No.12074424)the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China。
文摘The electronic evolution of Mott insulators into exotic correlated phases remains puzzling,because of electron interaction and inhomogeneity.Introduction of individual imperfections in Mott insulators could help capture the main mechanism and serve as a basis to understand the evolution.Here we utilize scanning tunneling microscopy to probe the atomic scale electronic structure of the spin-orbit-coupling assisted Mott insulator Sr_(3)Ir_(2)O_(7).It is found that the tunneling spectra exhibit a homogeneous Mott gap in defect-free regions,but near the oxygen vacancy in the rotated Ir O_(2)plane the local Mott gap size is significantly enhanced.We attribute the enhanced gap to the locally reduced hopping integral between the 5d electrons of neighboring Ir sites via the bridging planar oxygen p orbitals.Such bridging defects have a dramatic influence on local bandwidth,thus provide a new way to manipulate the strength of Mottness in a Mott insulator.
文摘The security of information is not assured over extended periods,especially with the rapid advancement of quantum computers.To address this challenge,quantum cryptography,rooted in quantum physics,offers comprehensive toolkits for key distribution[1],secret sharing[2],digital signatures[3]and other cryptographic tasks[4]with information-theoretical security.The feasibility of quantum cryptography,particularly quantum key distribution(QKD)。
基金supported by the National Key Research and Development Program of China(Grant No.2017YFA0302903)the National Natural Science Foundation of China(Grant Nos.11774422 and 11774424)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(Grant Nos.14XNLQ03 and 16XNLQ01)
文摘By using first-principles electronic structure calculations, we have studied the magnetic interactions in a proposed BaZn2P2-based diluted magnetic semiconductor(DMS). For a typical compound Ba(Zn(0.944)Mn(0.056))2P2 with only spin doping, due to the superexchange interaction between Mn atoms and the lack of itinerant carriers, the short-range antiferromagnetic coupling dominates. Partially substituting K atoms for Ba atoms, which introduces itinerant hole carriers into the p orbitals of P atoms so as to link distant Mn moments with the spin-polarized hole carriers via the p–d hybridization between P and Mn atoms, is very crucial for the appearance of ferromagnetism in the compound. Furthermore, applying hydrostatic pressure first enhances and then decreases the ferromagnetic coupling in(Ba0.75 K0.25)(Zn(0.944)Mn(0.056))2P2 at a turning point around 15 GPa, which results from the combined effects of the pressure-induced variations of electron delocalization and p–d hybridization. Compared with the BaZn2 As2-based DMS, the substitution of P for As can modulate the magnetic coupling effectively. Both the results for BaZn2 P2-based and BaZn2As2-based DMSs demonstrate that the robust antiferromagnetic(AFM) coupling between the nearest Mn–Mn pairs bridged by anions is harmful to improving the performance of these Ⅱ–Ⅱ–Ⅴ based DMS materials.
基金supported by Beijing Outstanding Scholar Programthe National Key Research and Development Program of China(Grant No. 2016YFA0301600)+3 种基金the National Natural Science Foundation of China(Grant No. 11734010)supported by a startup fund from UCSDsupported by the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China
文摘We train a neural network to identify impurities in the experimental images obtained by the scanning tunneling microscope(STM)measurements.The neural network is first trained with a large number of simulated data and then the trained neural network is applied to identify a set of experimental images taken at different voltages.We use the convolutional neural network to extract features from the images and also implement the attention mechanism to capture the correlations between images taken at different voltages.We note that the simulated data can capture the universal Friedel oscillation but cannot properly describe the non-universal physics short-range physics nearby an impurity,as well as noises in the experimental data.And we emphasize that the key of this approach is to properly deal with these differences between simulated data and experimental data.Here we show that even by including uncorrelated white noises in the simulated data,the performance of the neural network on experimental data can be significantly improved.To prevent the neural network from learning unphysical short-range physics,we also develop another method to evaluate the confidence of the neural network prediction on experimental data and to add this confidence measure into the loss function.We show that adding such an extra loss function can also improve the performance on experimental data.Our research can inspire future similar applications of machine learning on experimental data analysis.
基金Supported by the Ministry of Science and Technology of China under Grant Nos 2016YFA0300504,2017YFA0302904 and 2016YFA0301001the Natural Science Foundation of China under Grant Nos 11774419,11474357,11822412,11774423 and 11574394
文摘Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid(QSL), and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular lattice spin liquid candidate YbMgGaO_4 stimulated an increasing attention on the rare-earth-based frustrated magnets with strong spin-orbit coupling. Here we report the synthesis and characterization of a large family of rare-earth chalcogenides AReCh_2(A = alkali or monovalent ions, Re = rare earth, Ch = O,S,Se). The family compounds share the same structure(R3 m) as YbMgGaO_4,and antiferromagnetically coupled rare-earth ions form perfect triangular layers that are well separated along the c-axis. Specific heat and magnetic susceptibility measurements on NaYbO_2,NaYbS_2 and NaYbSe_2 single crystals and polycrystals, reveal no structural or magnetic transition down to 50 mK. The family, having the simplest structure and chemical formula among the known QSL candidates, removes the issue on possible exchange disorders in YbMgGaO_4. More excitingly, the rich diversity of the family members allows tunable charge gaps, variable exchange coupling, and many other advantages.This makes the family an ideal platform for fundamental research of QSLs and its promising applications.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0300504)the National Natural Science Foundation of China(Grant Nos.11574394,11774423,and 11822412)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(RUC)(Grant Nos.15XNLQ07,18XNLG14,and 19XNLG17)
文摘We report the detailed physical properties of quaternary compound Ba2BiFeS5 with the key structural ingredient of isolated FeS4 tetrahedra.Magnetization and heat capacity measurements clearly indicate that Ba2BiFeS5 has a paramagnetic to antiferromagnetic transition at about 30 K.The calculated magnetic entropy above ordering temperature is much smaller than theoretical value for high-spin Fe^3+ion with S=5/2,implying the possible short-range antiferromagnetic fluctuation in Ba2BiFeS5.
基金Supported by the National Key Research and Development Program of China under Grant Nos 2016YFA0401000 and2017YFA0302901the National Basic Research Program of China under Grant No 2015CB921000+2 种基金the National Natural Science Foundation of China under Grant Nos 11574371,11774399 and 11774398the Beijing Natural Science Foundation(Z180008)the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB28000000
文摘Growth of high-quality single crystals is of great significance for research of condensed matter physics. The exploration of suitable growing conditions for single crystals is expensive and time-consuming, especially for ternary compounds because of the lack of ternary phase diagram. Here we use machine learning(ML) trained on our experimental data to predict and instruct the growth. Four kinds of ML methods, including support vector machine(SVM), decision tree, random forest and gradient boosting decision tree, are adopted. The SVM method is relatively stable and works well, with an accuracy of 81% in predicting experimental results. By comparison,the accuracy of laboratory reaches 36%. The decision tree model is also used to reveal which features will take critical roles in growing processes.
基金Project supported by the National Science Foundation of China(Grant No.12174441)the Fundamental Research Funds for the Central Universities,Chinathe Research Funds of Remnin University of China(Grant No.18XNLG24)。
文摘We study the critical scaling and dynamical signatures of fractionalized excitations at two different deconfined quantum critical points(DQCPs)in an S=1/2 spin chain using the time evolution of infinite matrix product states.The scaling of the correlation functions and the dispersion of the conserved current correlations explicitly show the emergence of enhanced continuous symmetries at these DQCPs.The dynamical structure factors in several different channels reveal the development of deconfined fractionalized excitations at the DQCPs.Furthermore,we find an effective spin-charge separation at the DQCP between the ferromagnetic(FM)and valence bond solid(VBS)phases,and identify two continua associated with different types of fractionalized excitations at the DQCP between the X-direction and Z-direction FM phases.Our findings not only provide direct evidence for the DQCP in one dimension but also shed light on exploring the DQCP in higher dimensions.
基金Project supported by the Ministry of Science and Technology of China,the National Key R&D Program of China(Grant No.2016YFA0300504)the National Natural Science Foundation of China(Grant No.11674392)+3 种基金the Research Funds of Remnin University of China(Grant No.18XNLG24)part supported by the NSF Grant DMR-1920740the Robert A.Welch Foundation Grant C-1411support by a Ulam Scholarship from the Center for Nonlinear Studies at Los Alamos National Laboratory
文摘Motivated by the growing interest in the novel quantum phases in materials with strong electron correlations and spin–orbit coupling, we study the interplay among the spin–orbit coupling, Kondo interaction, and magnetic frustration of a Kondo lattice model on a two-dimensional honeycomb lattice.We calculate the renormalized electronic structure and correlation functions at the saddle point based on a fermionic representation of the spin operators.We find a global phase diagram of the model at half-filling, which contains a variety of phases due to the competing interactions.In addition to a Kondo insulator, there is a topological insulator with valence bond solid correlations in the spin sector, and two antiferromagnetic phases.Due to the competition between the spin–orbit coupling and Kondo interaction, the direction of the magnetic moments in the antiferromagnetic phases can be either within or perpendicular to the lattice plane.The latter antiferromagnetic state is topologically nontrivial for moderate and strong spin–orbit couplings.
基金The ARPES experimental work is supported by the National Natural Science Foundation of China(Grant No.11574360)the National Basic Research Program of China(Grant Nos.2015CB921300,2013CB921700,and 2013CB921904)+3 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB07020300)supported by the National Natural Science Foundation of China(Grant No.91421304)the Fundamental Research Funds for the Central Universities of Chinathe Research Funds of Renmin University of China(Grant Nos.14XNLQ03 and16XNLQ01)
文摘We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7that exhibits stronger two-dimensional character than the prototypical heavy fermion system CeCoIn5.Multiple Fermi surface sheets and a complex band structure are clearly resolved. We have also performed detailed band structure calculations on CePt2In7. The good agreement found between our measurements and the calculations suggests that the band renormalization effect is rather weak in CePt2In7. A comparison of the common features of the electronic structure of CePt2In7and CeCoIn5indicates that CeCoIn5shows a much stronger band renormalization effect than CePt2In7. These results provide new information for understanding the heavy fermion behaviors and unconventional superconductivity in Ce-based heavy fermion systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.11190024 and 11404383)the National Basic Research Program of China(Grant No.2011CBA00112)+1 种基金the Fundamental Research Funds for the Central Universities,Chinathe Research Funds of Renmin University of China(Grant No.14XNLQ03)
文摘The discovery of high temperature superconductivity in FeSe films on SrTiO3 substrate has inspired great experimen- tal and theoretical interests. First-principles density functional theory calculations, which have played an important role in the study of bulk iron-based superconductors, also participate in the investigation of interfacial superconductivity. In this article, we review the calculation results on the electronic and magnetic structures of FeSe epitaxial films, emphasiz- ing on the interplay between different degrees of freedom, such as charge, spin, and lattice vibrations. Furthermore, the comparison between FeSe monolayer and bilayer films on SrTiO3 is discussed.
基金Project supported by the National Natural Science Foundation of China(Grant No.11674392)the Ministry of Science and Technology of China,National Program on Key Research Project(Grant No.2016YFA0300504)the Research Funds of Remnin University of China(Grant No.18XNLG24).
文摘In quasi-one-dimensional(q1D) quantum antiferromagnets, the complicated interplay of intrachain and interchain exchange couplings may give rise to rich phenomena. Motivated by recent progress on field-induced phase transitions in the q1D antiferromagnetic(AFM) compound YbAlO3, we study the phase diagram of spin-1/2 Heisenberg chains with Ising anisotropic interchain couplings under a longitudinal magnetic field via large-scale quantum Monte Carlo simulations,and investigate the role of the spin anisotropy of the interchain coupling on the ground state of the system. We find that the Ising anisotropy of the interchain coupling can significantly enhance the longitudinal spin correlations and drive the system to an incommensurate AFM phase at intermediate magnetic fields, which is understood as a longitudinal spin density wave(LSDW). With increasing field, the ground state changes to a canted AFM order with transverse spin correlations. We further provide a global phase diagram showing how the competition between the LSDW and the canted AFM states is tuned by the Ising anisotropy of the interchain coupling.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFA0300504)the National Natural Science Foundation of China(Grant Nos.11574394,11774423,and 11822412)+1 种基金the Fundamental Research Funds for the Central Universities of Chinathe Research Funds of Renmin University of China(RUC)(Grant Nos.15XNLQ07,18XNLG14,and 19XNLG17)
文摘We present the experiment observation of a giant topological Hall effect(THE)in a frustrated kagome bilayer magnet Fe3Sn2.The negative topologically Hall resistivity appears when the field is below 1.3 T and it increases with increasing temperature up to 300 K.Its maximum absolute value reaches^2.01μΩ·cm at 300 K and 0.76 T.The origins of the observed giant THE can be attributed to the coexistence of the field-induced skyrmion state and the non-collinear spin configuration,possibly related to the magnetic frustration interaction in Fe3Sn2.
基金supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0302904 and 2016YFA0300504)the National Natural Science Foundation of China (Grant Nos. U1932215 and 11774419)+2 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No. XDB33010100)Postdoctoral Science Foundation of China (Grant No. 2020M670500)the support from Users with Excellence Program of Hefei Science Center and High Magnetic Field Facility,CAS
文摘Recently rare-earth chalcogenides have been revealed as a family of quantum spin liquid(QSL)candidates hosting a large number of members.In this paper we report the crystal growth and magnetic measurements of KErTe_(2),which is the first member of telluride in the family.Compared to its cousins of oxides,sulfides and selenides,KErTe_(2) retains the high symmetry of R3m and Er3+ions still sit on a perfect triangular lattice.The separation between adjacent magnetic layers is expectedly increased,which further enhances the two dimensionality of the spin system.Specific heat and magnetic susceptibility measurements on KErTe_(2) single crystals reveal no structural and magnetic transition down to 1.8 K.Most interestingly,the absorption spectrum shows that the charge gap of KErTe_(2) is roughly 0.93±0.35 eV,which is the smallest among all the reported members in the family.This immediately invokes the interest towards metallization even superconductivity using the compound.
基金This work is supported by the National Natural Science Foundation of China(Grant Nos.11874295,11875219,11705141,11905169,and 11875319)the National Key R&D Program of China(Grant Nos.2018YFA0404801 and 2018YFA0404802)+1 种基金Chinese Science Challenge Project No.TZ2016005National Key Research and Development Project No.2019YFA0404900.
文摘The generation of highly polarized high-energy brilliantγ-rays via laser–plasma interaction is investigated in the quantum radiation-reaction regime.We employ a quantum electrodynamics particle-in-cell code to describe spin-resolved electron dynamics semiclassically and photon emission and polarization quantum mechanically in the local constant field approximation.As an ultrastrong linearly polarized(LP)laser pulse irradiates a near-critical-density(NCD)plasma followed by an ultrathin planar aluminum target,the electrons in the NCD plasma are first accelerated by the driving laser to ultrarelativistic energies and then collide head-on with the laser pulse reflected by the aluminum target,emitting brilliant LPγ-rays via nonlinear Compton scattering with an average polarization of about 70%and energy up to hundreds of MeV.Suchγ-rays can be produced with currently achievable laser facilities and will find various applications in high-energy physics and laboratory astrophysics.
基金the National Natural Science Foundation of China (Grant Nos. 11574394, 11774423, 11822412, and 51608273)the Fundamental Research Funds for the Central Universities (Grant No. 2017RC20)+3 种基金the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (No. 16KJB560008)the Young Researcher Program Nanjing Forestry University of China (No. CX2016023)Key Laboratory of Advanced Building Materials of Anhui Province of China (No. JZCL201603KF)State Key Laboratory of High Performance Civil Engineering Materials of China (No. 2016CEM004).
文摘We have synthesized and investigated physical properties of two new quaternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals, which are isostructural to Tb2NiAl4Ge2 and Er2CoAl4Ge2. The most important structural feature of these materials is the anti-CaF2-type CoAl4T2 slabs. These materials show metallic behavior below 300 K and there is a long-range antiferromagnetic (AFM) transition appearing at 20 and 27 K for GdCoAl4Ge2 and Gd2CoAl4Si2, respectively. Resistivity and heat capacity measurements also confirm these bulk AFM transitions. Further analysis indicates that this long-range antiferromagnetism should result from the magnetic interaction between local moments of Gd^3+ ions.