Magneto-transport properties of insulating bulk states in Bi（111） films are systematically investigated under the parallel field （BⅡ）. We find that the magnetotransport of the Bll field is a more powerful tool to...Magneto-transport properties of insulating bulk states in Bi（111） films are systematically investigated under the parallel field （BⅡ）. We find that the magnetotransport of the Bll field is a more powerful tool to distinguish the bulk states and the surface states. A large magnetoresistance （MR） up to 20% in the BⅡ field is induced by the insulating bulk states for the suppression of the backward scattering. With the increasing thickness, a positive MR（BⅡ） from magnetic induced boundary scattering appears in the semimetal films. As the thickness is reduced to 1Ohm, the positive MR（BⅡ） is induced by weak anti-localization from the surface states.展开更多
We theoretically investigate the single- and few-electron states in deformed HgTe quantum dots （QDs） with an inverted band structure using the full configuration interaction method. For the circular and deformed QD,...We theoretically investigate the single- and few-electron states in deformed HgTe quantum dots （QDs） with an inverted band structure using the full configuration interaction method. For the circular and deformed QD, it is found that the energy of edge states is robust against the shape from the circular QD in various elliptic ones. For the few electron states, electrons will firstly fill the edge states localized at the short axis, then the states localized at the long axis of the QD before filling the bulk states. The filling of the edge states can be controlled by tuning the dot size or the deformation of the geometry of the HgTe QD, respectively.展开更多
We develop a tractable theoretical model to investigate the thermoelectric （TE） transport properties of surface states in topological insulator thin films （TITFs） of Bi2Sea at room temperature. The hybridization b...We develop a tractable theoretical model to investigate the thermoelectric （TE） transport properties of surface states in topological insulator thin films （TITFs） of Bi2Sea at room temperature. The hybridization between top and bottom surface states in the TITF plays a significant role. With the increasing hybridization-induced surface gap, the electrical conductivity and electron thermal conductivity decrease while the Seebeck coefficient increases. This is due to the metal-semiconductor transition induced by the surface-state hybridization. Based on these TE transport coefficients, the TE figure-of-merit ZT is evaluated. It is shown that ZT can be greatly improved by the surface-state hybridization. Our theoretical results are pertinent to the exploration of the TE transport properties of surface states in TITFs and to the potential application of Bi2Sea-based TITFs as high-performance TE materials and devices.展开更多
Using the natural orbitals renormalization group（NORG）method,we investigate the screening of the local spin of an Anderson impurity interacting with the helical edge states in a quantum spin Hall insulator.It is fou...Using the natural orbitals renormalization group（NORG）method,we investigate the screening of the local spin of an Anderson impurity interacting with the helical edge states in a quantum spin Hall insulator.It is found that there is a local spin formed at the impurity site and the local spin is completel.y screened by electrons in the quantum spin Hall insulator.Meanwhile,the local spin is screened dominantly by a single active natural orbital.We then show that the Kondo screening mechanism becomes transparent and simple in the framework of the natural orbitals formalism.We project the active natural orbital respectively into real space and momentum space to characterize its structure.We conilrm the spin-momentum locking property of the edge states based on the occupancy of a Bloch state on the edge to which the impurity couples.Furthermore,we study the dynamical property of the active natural orbital represented by the local density of states,from which we observe the Kondo resonance peak.展开更多
Rhombohedral multilayer graphene(RMG)has recently been demonstrated to be an exceptional research platform hosting a wide range of quantum phenomena.These include superconductivity[1],various symmetry-broken states(sp...Rhombohedral multilayer graphene(RMG)has recently been demonstrated to be an exceptional research platform hosting a wide range of quantum phenomena.These include superconductivity[1],various symmetry-broken states(spin,valley,and layer)[2],integer and fractional quantum anomalous Hall effect[3],and Chen insulator states[4].A key factor in tuning the properties of RMG is the number of layers,as different quantum phases have been observed only in samples with specific layer counts.For example,the fractional Chern insulator phase has been observed exclusively in a 5-layer sample[5],the quantum anomalous Hall in a 4-layer sample[3],and superconductivity in a 3-layer sample[1].展开更多
Topological insulating states in 2-dimensional(2D)materials are ideal systems to study different types of quantized response signals due to their in gap metallic states.Very recently,the quantum spin Hall effect was d...Topological insulating states in 2-dimensional(2D)materials are ideal systems to study different types of quantized response signals due to their in gap metallic states.Very recently,the quantum spin Hall effect was discovered in monolayer TalrTe Via the observation of quantized longitudinal conductance that rarely exists in other 2D topological insulators.The nontrivial Z_(2)topological charges can exist at both charge neutrality point and the van Hove singularity point with correlation-effect-induced bandgap.On the basis of this model 2D material,we studied the switch of quantized signals between longitudinal conductance and transversal Hall conductance via tuning external magnetic field.In Z_(2)topological phase of monolayer TalrTe_(4),the zero Chern number can be understood as 1-1=O from the double band inversion from spinup and spin-down channels.After applying a magnetic field perpendicular to the plane,the Zeeman split changes the band order for one branch of the band inversion from spin-up and spin-down channels,along with a sign charge of the Berry phase.Then,the net Chern number of 1-1=0 is tuned to 1+1=2 or-1-1=-2 depending on the orientation of the magnetic field.The quantized signal not only provides another effective method for the verification of topological state in monolayer TalrTe_(4)but also offers a strategy for the utilization of the new quantum topological states based on switchable quantized responses.展开更多
In order to effectively utilize the dielectric response characteristics of transformers to diagnose the insulation state,this paper proposes a two-level hybrid optimization method for analyzing time-domain dielectric ...In order to effectively utilize the dielectric response characteristics of transformers to diagnose the insulation state,this paper proposes a two-level hybrid optimization method for analyzing time-domain dielectric response characteristics.The optimization algorithm is based on the combined statistical indicators(CSI)and random forest(RF)theory.The initial feature space set is formed with 23 time-domain characteristics.In the first-level stage,statistical indices correlation,distance,and information indicators are integrated to assess the synthesis score of the characteristics,while highly redundant and lowclass discrimination characteristics are eliminated from the initial space set.In the second-level stage,the Random Forest based outside bagging data theory is introduced to evaluate the least important characteristics,and the characteristics with low importance indices are excluded to obtain the final optimal feature space set.The proposed method is carried out on 82 sets of data from actual dielectric response tests on oil-paper insulation transformers.Finally,the final optimal feature space set,along with several other data sets,is tested via different diagnosis methods.The results show that the optimal feature space set obtained via the proposed method outperforms other feature space sets in terms of better adaptability and diagnosis accuracy.展开更多
Broadband photodetectors with self-driven functions have attracted intensive scientific interest due to their low energy consumption and high optical gain.However,high-performance broadband self-driven photodetectors ...Broadband photodetectors with self-driven functions have attracted intensive scientific interest due to their low energy consumption and high optical gain.However,high-performance broadband self-driven photodetectors are still a significant challenge due to the complex fabrication processes,environmental toxicity,high production costs of traditional 3D semiconductor materials and sharply raised contact resistance,severe interfacial recombination of 2D materials and 2D/3D mixed dimension heterojunction.Here,1D p-Te/2D n-Bi_(2)Te_(3) heterojunctions are constructed by the simple and low-cost hydrothermal method.1D p-Te/2D n-Bi_(2)Te_(3) devices are applied in photoelectrochemical(PEC)photodetectors,with their high performance attributed to the good interfacial contacts reducing interface recombination.The device demonstrated a broad wavelength range(365–850 nm)with an Iph/Idark as high as 377.45.The R_(i),D^(*),and external quantum efficiency(EQE)values of the device were as high as 12.07 mA/W,5.87×10^(10) Jones,and 41.05%,respectively,which were significantly better than the performance of the prepared Bi_(2)Te_(3) and Te devices.A comparison of the freshly fabricated device and the device after 30 days showed that 1D p-Te/2D n-Bi_(2)Te_(3) had excellent stability with only 18.08%decay of photocurrent.It is anticipated that this work will provide new emerging material for future design and preparation of a high-performance self-driven broadband photodetector.展开更多
In this work, epitaxial growth of LaMnO3 thin films on different substrates using pulsed laser deposition under tensile and compressive strain was studied. The intrinsic exchange bias effect was observed in the single...In this work, epitaxial growth of LaMnO3 thin films on different substrates using pulsed laser deposition under tensile and compressive strain was studied. The intrinsic exchange bias effect was observed in the single A-type antiferromagnetic LaMnO3 films no matter whether the tensile or compressive strain was supplied by the substrates. Due to the lattice mismatch between the film and different substrates, the intense strain can induce MnO6 octahedral rotation in the bottom region of the film neighboring the substrate, which leads to the distortion of MnO6 octahedron and the net magnetic behavior. However, the upper part maintains the original A-type antiferromagnetic order due to strain relaxation. The exchange bias effect in single films is attributed to the coupling between the bottom canted magnetic part and the upper antiferromagnetic region. The observation of exchange bias in single films on different substrates enables the emergence of a new class of biasing components in spintronics, which are based on strain-engineering.展开更多
基金Supported by the Fundamental Research Funds for the Central Universities,and the Research Funds of Renmin University of China under Grant No 10XNF086
文摘Magneto-transport properties of insulating bulk states in Bi（111） films are systematically investigated under the parallel field （BⅡ）. We find that the magnetotransport of the Bll field is a more powerful tool to distinguish the bulk states and the surface states. A large magnetoresistance （MR） up to 20% in the BⅡ field is induced by the insulating bulk states for the suppression of the backward scattering. With the increasing thickness, a positive MR（BⅡ） from magnetic induced boundary scattering appears in the semimetal films. As the thickness is reduced to 1Ohm, the positive MR（BⅡ） is induced by weak anti-localization from the surface states.
基金Supported by the National Natural Science Foundation of China under Grant No 11434010the National Basic Research Program of China under Grant No 2011CB922204
文摘We theoretically investigate the single- and few-electron states in deformed HgTe quantum dots （QDs） with an inverted band structure using the full configuration interaction method. For the circular and deformed QD, it is found that the energy of edge states is robust against the shape from the circular QD in various elliptic ones. For the few electron states, electrons will firstly fill the edge states localized at the short axis, then the states localized at the long axis of the QD before filling the bulk states. The filling of the edge states can be controlled by tuning the dot size or the deformation of the geometry of the HgTe QD, respectively.
基金Supported by the National Natural Science Foundation of China under Grant No 11304316the Ministry of Science and Technology of China under Grant No 2011YQ130018the Department of Science and Technology of Yunnan Province,and the Chinese Academy of Sciences
文摘We develop a tractable theoretical model to investigate the thermoelectric （TE） transport properties of surface states in topological insulator thin films （TITFs） of Bi2Sea at room temperature. The hybridization between top and bottom surface states in the TITF plays a significant role. With the increasing hybridization-induced surface gap, the electrical conductivity and electron thermal conductivity decrease while the Seebeck coefficient increases. This is due to the metal-semiconductor transition induced by the surface-state hybridization. Based on these TE transport coefficients, the TE figure-of-merit ZT is evaluated. It is shown that ZT can be greatly improved by the surface-state hybridization. Our theoretical results are pertinent to the exploration of the TE transport properties of surface states in TITFs and to the potential application of Bi2Sea-based TITFs as high-performance TE materials and devices.
基金Supported by National Natural Science Foundation of China under Grant Nos 11474356 and 11774422supported by the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China
文摘Using the natural orbitals renormalization group（NORG）method,we investigate the screening of the local spin of an Anderson impurity interacting with the helical edge states in a quantum spin Hall insulator.It is found that there is a local spin formed at the impurity site and the local spin is completel.y screened by electrons in the quantum spin Hall insulator.Meanwhile,the local spin is screened dominantly by a single active natural orbital.We then show that the Kondo screening mechanism becomes transparent and simple in the framework of the natural orbitals formalism.We project the active natural orbital respectively into real space and momentum space to characterize its structure.We conilrm the spin-momentum locking property of the edge states based on the occupancy of a Bloch state on the edge to which the impurity couples.Furthermore,we study the dynamical property of the active natural orbital represented by the local density of states,from which we observe the Kondo resonance peak.
基金the National Natural Science Foundation of China(92365204,12274298,52025023,and12304217)the National Key R&D Program of China(2022YFA1604400/03 and 2022YFA1403500/04)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDB33000000)Fundamental Research Funds for the Central Universities from Chinathe New Cornerstone Science Foundation through the XPLORER PRIZE。
文摘Rhombohedral multilayer graphene(RMG)has recently been demonstrated to be an exceptional research platform hosting a wide range of quantum phenomena.These include superconductivity[1],various symmetry-broken states(spin,valley,and layer)[2],integer and fractional quantum anomalous Hall effect[3],and Chen insulator states[4].A key factor in tuning the properties of RMG is the number of layers,as different quantum phases have been observed only in samples with specific layer counts.For example,the fractional Chern insulator phase has been observed exclusively in a 5-layer sample[5],the quantum anomalous Hall in a 4-layer sample[3],and superconductivity in a 3-layer sample[1].
基金supported by the Foundation from Liaoning Province(grant no.XLYC2203080)the National Natural Science Foundation of China(grant nos.52271016 and 52188101)the National Key R&D Program of China(grant no.2021YFB3501503)。
文摘Topological insulating states in 2-dimensional(2D)materials are ideal systems to study different types of quantized response signals due to their in gap metallic states.Very recently,the quantum spin Hall effect was discovered in monolayer TalrTe Via the observation of quantized longitudinal conductance that rarely exists in other 2D topological insulators.The nontrivial Z_(2)topological charges can exist at both charge neutrality point and the van Hove singularity point with correlation-effect-induced bandgap.On the basis of this model 2D material,we studied the switch of quantized signals between longitudinal conductance and transversal Hall conductance via tuning external magnetic field.In Z_(2)topological phase of monolayer TalrTe_(4),the zero Chern number can be understood as 1-1=O from the double band inversion from spinup and spin-down channels.After applying a magnetic field perpendicular to the plane,the Zeeman split changes the band order for one branch of the band inversion from spin-up and spin-down channels,along with a sign charge of the Berry phase.Then,the net Chern number of 1-1=0 is tuned to 1+1=2 or-1-1=-2 depending on the orientation of the magnetic field.The quantized signal not only provides another effective method for the verification of topological state in monolayer TalrTe_(4)but also offers a strategy for the utilization of the new quantum topological states based on switchable quantized responses.
基金supported by The National Natural Science Foundation of China(61174117)the Foundation of Scientific Research Project of Jinjiang Science and Education Development Center of Fuzhou Univerdity(2019-JJFDKY-33).
文摘In order to effectively utilize the dielectric response characteristics of transformers to diagnose the insulation state,this paper proposes a two-level hybrid optimization method for analyzing time-domain dielectric response characteristics.The optimization algorithm is based on the combined statistical indicators(CSI)and random forest(RF)theory.The initial feature space set is formed with 23 time-domain characteristics.In the first-level stage,statistical indices correlation,distance,and information indicators are integrated to assess the synthesis score of the characteristics,while highly redundant and lowclass discrimination characteristics are eliminated from the initial space set.In the second-level stage,the Random Forest based outside bagging data theory is introduced to evaluate the least important characteristics,and the characteristics with low importance indices are excluded to obtain the final optimal feature space set.The proposed method is carried out on 82 sets of data from actual dielectric response tests on oil-paper insulation transformers.Finally,the final optimal feature space set,along with several other data sets,is tested via different diagnosis methods.The results show that the optimal feature space set obtained via the proposed method outperforms other feature space sets in terms of better adaptability and diagnosis accuracy.
基金supported by the National Key Research and Development Program of China(No.2019YFA0705201)the National Natural Science Foundation of China(No.U2032129).
文摘Broadband photodetectors with self-driven functions have attracted intensive scientific interest due to their low energy consumption and high optical gain.However,high-performance broadband self-driven photodetectors are still a significant challenge due to the complex fabrication processes,environmental toxicity,high production costs of traditional 3D semiconductor materials and sharply raised contact resistance,severe interfacial recombination of 2D materials and 2D/3D mixed dimension heterojunction.Here,1D p-Te/2D n-Bi_(2)Te_(3) heterojunctions are constructed by the simple and low-cost hydrothermal method.1D p-Te/2D n-Bi_(2)Te_(3) devices are applied in photoelectrochemical(PEC)photodetectors,with their high performance attributed to the good interfacial contacts reducing interface recombination.The device demonstrated a broad wavelength range(365–850 nm)with an Iph/Idark as high as 377.45.The R_(i),D^(*),and external quantum efficiency(EQE)values of the device were as high as 12.07 mA/W,5.87×10^(10) Jones,and 41.05%,respectively,which were significantly better than the performance of the prepared Bi_(2)Te_(3) and Te devices.A comparison of the freshly fabricated device and the device after 30 days showed that 1D p-Te/2D n-Bi_(2)Te_(3) had excellent stability with only 18.08%decay of photocurrent.It is anticipated that this work will provide new emerging material for future design and preparation of a high-performance self-driven broadband photodetector.
基金financially supported by the National Key R&D Program of China (2017YFB0405703)the National Natural Science Foundation of China (51871137, 61434002 and 51571136)the Special Funds of Sanjin Scholars Program
文摘In this work, epitaxial growth of LaMnO3 thin films on different substrates using pulsed laser deposition under tensile and compressive strain was studied. The intrinsic exchange bias effect was observed in the single A-type antiferromagnetic LaMnO3 films no matter whether the tensile or compressive strain was supplied by the substrates. Due to the lattice mismatch between the film and different substrates, the intense strain can induce MnO6 octahedral rotation in the bottom region of the film neighboring the substrate, which leads to the distortion of MnO6 octahedron and the net magnetic behavior. However, the upper part maintains the original A-type antiferromagnetic order due to strain relaxation. The exchange bias effect in single films is attributed to the coupling between the bottom canted magnetic part and the upper antiferromagnetic region. The observation of exchange bias in single films on different substrates enables the emergence of a new class of biasing components in spintronics, which are based on strain-engineering.
