With a large number of researches being conducted on two?dimen?sional(2D) materials, their unique properties in optics, electrics, mechanics, and magnetics have attracted increasing attention. Accordingly, the idea of...With a large number of researches being conducted on two?dimen?sional(2D) materials, their unique properties in optics, electrics, mechanics, and magnetics have attracted increasing attention. Accordingly, the idea of combining distinct functional 2D materials into heterostructures naturally emerged that pro?vides unprecedented platforms for exploring new physics that are not accessible in a single 2D material or 3D heterostructures. Along with the rapid development of controllable, scalable, and programmed synthesis techniques of high?quality 2D heterostructures, various heterostructure devices with extraordinary performance have been designed and fabricated, including tunneling transistors, photodetectors, and spintronic devices. In this review, we present a summary of the latest progresses in fabrications, properties, and applications of di erent types of 2D heterostruc?tures, followed by the discussions on present challenges and perspectives of further investigations.展开更多
We conduct a detailed examination of the magnetic and electrical transport properties in GdAlSi and SmAlGe crystals,which possess a LaPtSi-type structure(space group I4_(1)md).The magnetic susceptibility data unambigu...We conduct a detailed examination of the magnetic and electrical transport properties in GdAlSi and SmAlGe crystals,which possess a LaPtSi-type structure(space group I4_(1)md).The magnetic susceptibility data unambiguously reveal magnetic ordering below a characteristic transition temperature(T_(N)).For GdAlSi,a hysteresis loop is observed in the magnetization and magnetoresistance curves within the ab plane when the magnetic field is applied below T_(N),which is around32 K.Notable specific heat anomalies are detected at 32 K for GdAlSi and 6 K for SmAlGe,confirming the occurrence of magnetic transitions.In addition,the extracted magnetic entropy at high temperatures is consistent with the theoretical value of Rln(2J+1) for J=7/2 in Gd^(3+) and J=5/2 in Sm^(3+),respectively.SmAlGe also exhibits Schottky-like specific heat contributions.Additionally,both GdAlSi and SmAlGe exhibit positive magnetoresistance and a normal Hall effect.展开更多
Over the last few years,researches in iridates have developed into an exciting field with the discovery of numerous emergent phenomena,interesting physics,and intriguing functionalities.Among the studies,iridate-based...Over the last few years,researches in iridates have developed into an exciting field with the discovery of numerous emergent phenomena,interesting physics,and intriguing functionalities.Among the studies,iridate-based artificial structures play a crucial role owing to their extreme flexibility and tunability in lattice symmetry,chemical composition,and crystal dimensionality.In this article,we present an overview of the recent progress regarding iridate-based artificial structures.We first explicitly introduce several essential concepts in iridates.Then,we illustrate important findings on representative SrIrO_(3)/SrTiO_(3) superlattices,heterostructures comprised of SrIrO3 and magnetic oxides,and their response to external electric-field stimuli.Finally,we comment on existing problems and promising future directions in this exciting field.展开更多
We theoretically investigate the quantum interference theory of magnetotransport of the three-component or spin-1 chiral fermions, which possess two linear Dirac bands and a flat band. For isotropic scalar impurities,...We theoretically investigate the quantum interference theory of magnetotransport of the three-component or spin-1 chiral fermions, which possess two linear Dirac bands and a flat band. For isotropic scalar impurities, the correction of conductivity from the coherent backscatter and non-coherent backscatter contributions cancel out in the intravalley scattering, leading to a weak localization correction to the Drude conductivity from the intervalley scattering. For the anisotropic impurities, the above cancelation is removed, we find the approximative quantum interference conductivity in the weak anisotropy case. The contributions from the chiral anomaly and classical Lorentz force are also discussed. Our work reveals some intriguing and detectable transport signatures of the novel spin-1 chiral fermions.展开更多
Layered transition metal dichalcogenides(TMDCs)have been extensively studied owing to their unique physical and chemical properties.Weak van der Waals(vdW)interact!ons betwee n the stacki ng layers of TMDCs allow inte...Layered transition metal dichalcogenides(TMDCs)have been extensively studied owing to their unique physical and chemical properties.Weak van der Waals(vdW)interact!ons betwee n the stacki ng layers of TMDCs allow intercalati on of various species including mono vale nt alkali,divale nt alkaline earth and multivale nt metal ions,zero-vale nt transiti on metals,as well as orga nic molecules,all of which can drastically alter fun dame ntal properties of the TMDCs.The urge to understa nd the phe nomena and the desire to exploit them for applicati ons have inspired a great deal of investigations.A large portion of the mystery has been unveiled over the past decade of intense research;however,many questions remain open and require further explorations.This review is concerned with investigations on structural and electronic evolution of TMDCs drive n by electrochemically con trolled in tercalati ons.Herein,we aim to survey the rece nt adva nces and experime ntal platforms for mon itoring the in tercalati on processes in situ by utilizi ng nano devices.In additi on,several in quiries and prospects are outlined in a broader con text for future ave nues of studies.展开更多
The superconductivity and nontrivial topological electronic state are key hallmarks of topological superconductors.Here,we focus on the transport signals of possible topological surface state in the topological superc...The superconductivity and nontrivial topological electronic state are key hallmarks of topological superconductors.Here,we focus on the transport signals of possible topological surface state in the topological superconductor candidate β-PdBi_(2) nanoflake with a thickness of 21 nm.The resistance demonstrates a semiconductor-metal transition followed by an upturned behavior as the temperature decreases.A large and unsaturated longitudinal magnetoresistance(MR),accompanied by distinct Shubnikov-de Hass oscillation in Hall resistance,is observed.An analysis of Hall resistance reveals that the carriers present the characteristics of relativistic particles with small effective mass and extremely high mobility.The angle-dependent quantum oscillations demonstrate a two-dimensional Fermi surface topology.A giant anisotropic MR as large as 98%is detected when rotating the magnetic field.These results provide the possible transport signals of a nontrivial topological electronic state,establishing a further understanding of the topological properties of the low-dimensional topological superconductor candidate β-PdBi_(2).展开更多
Simulations are performed on clusters of finite size to study the effects of size and current-path structure on magnetotransport in spatially-confined samples. Magnetotransport networks are established and calculated ...Simulations are performed on clusters of finite size to study the effects of size and current-path structure on magnetotransport in spatially-confined samples. Magnetotransport networks are established and calculated based on fractal structures including Koch curves and percolation backbones extracted from regular lattices. The structure pattern of clusters is shown to play an important role in the magnetotransport behaviours by affecting the magnetore- sistance fluctuations due to spin disorder in the systems of small size, which suggests the possibility of controlling the magnetotransport by the design of current-path configurations.展开更多
Base optimum thickness is determined for a front illuminated bifacial silicon solar cell n<sup>+</sup>-p<span style="font-size:10px;">-</span>p<sup>+</sup> under magnetic ...Base optimum thickness is determined for a front illuminated bifacial silicon solar cell n<sup>+</sup>-p<span style="font-size:10px;">-</span>p<sup>+</sup> under magnetic field. From the magneto transport equation relative to excess minority carriers in the base, with specific boundary conditions, the photocurrent is obtained. From this result the expressions of the carrier’s recombination velocity at the back surface are deducted. These new expressions of recombination velocity are plotted according to the depth of the base, to deduce the optimum thickness, which will allow the production, of a high short-circuit photocurrent. Calibration relationships of optimum thickness versus magnetic field were presented according to study ranges. It is found that, applied magnetic field imposes a weak thickness material for solar cell manufacturing leading to high short-circuit current.展开更多
Resistivity, magnetoresistivity and Hall effect measurements in n-type Te-doped GaSb grown by the liquid encapsuled Czochralski technique are carried out as functions of temperature （35-350 K） and magnetic field （0...Resistivity, magnetoresistivity and Hall effect measurements in n-type Te-doped GaSb grown by the liquid encapsuled Czochralski technique are carried out as functions of temperature （35-350 K） and magnetic field （0-1.35 T）. The power law model is used to explain the temperature-dependent resistivity. The magnetic-field-dependent data are analysed using the quantitative mobility spectrum analysis technique. The effect of individual band parameters （nL, nr, μL, μr, p and μp） on both the electron and magneto transports have been discussed. The EL - Er energy separation between the L and conduction band edges is also derived.展开更多
A series of bulk polycrystalline La1-xLixMnO3 samples with x ranging from 0.1 to 0.5 was prepared by sol-gel method,X-ray diffraction patterns show that the crystal structures are single rhombohedral perorskite for th...A series of bulk polycrystalline La1-xLixMnO3 samples with x ranging from 0.1 to 0.5 was prepared by sol-gel method,X-ray diffraction patterns show that the crystal structures are single rhombohedral perorskite for the x≤0.3 sample and the impurity appears when x〉0.3.Under the same synthesized conditions,the higher Li content samples display a higher content of liquid phase content and larger mean grain sizes,which leads to the increases of the effect of the grain boundaries.The experimental results show that the change of the ferromagnetic transition temperature and the resistivity can attribute to the effect of the grain boundary and the connectivity of the inter grains as well as the ratio of Mn^3＋ to Mn^4＋.展开更多
The LaMn1-xTexO3+δ (x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3+ io...The LaMn1-xTexO3+δ (x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3+ ions are partly converted into Mn2+ and Mn4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn2+, Mn3+ and Mn4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn3+ is much larger or less than the sum of Mn2+ and Mn4+; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn3+ is close to the sum of Mn2+ and Mn4+. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism.展开更多
Exchange coupling between topological insulator and ferromagnetic insulator through proximity effect is strongly attractive for both fundamental physics and technological applications. Here we report a comprehensive i...Exchange coupling between topological insulator and ferromagnetic insulator through proximity effect is strongly attractive for both fundamental physics and technological applications. Here we report a comprehensive investigation on the growth behaviors of prototype topological insulator Bi2Se3 thin film on a single-crystalline LaCoO3 thin film on SrTiO3 substrate, which is a strain-induced ferromagnetic insulator. Different from the growth on other substrates, the Bi2Se3 films with highest quality on LaCoO3 favor a relatively low substrate temperature during growth. As a result, an inverse dependence of carrier mobility with the substrate temperature is found. Moreover, the magnetoresistance and coherence length of weak antilocalization also have a similar inverse dependence with the substrate temperature, as revealed by the magnetotransport measurements. Our experiments elucidate the special behaviors in Bi2Se3/LaCoO3 heterostructures, which provide a good platform for exploring related novel quantum phenomena, and are inspiring for device applications.展开更多
Magnetotransport measurements are carried out on the A1GaN/A1N/GaN in an SiC heterostructure, which demon- strates the existence of the high-quality two-dimensional electron gas （2DGE） at the A1N/GaN interface. Whil...Magnetotransport measurements are carried out on the A1GaN/A1N/GaN in an SiC heterostructure, which demon- strates the existence of the high-quality two-dimensional electron gas （2DGE） at the A1N/GaN interface. While the carrier concentration reaches 1.32×10^13 cm^-2 and stays relatively unchanged with the decreasing temperature, the mobility of the 2DEG increases to 1.21 × 10^4 cm2/（V.s） at 2 K. The Shubnikov-de Haas （SdH） oscillations are observed in a magnetic field as low as 2.5 T at 2 K. By the measurements and the analyses of the temperature-dependent SdH oscillations, the effective mass of the 2DEC is determined. The ratio of the transport lifetime to the quantum scattering time is 9 in our sample, indicating that small-angle scattering is predominant.展开更多
An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters. Two of these intrinsic par...An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters. Two of these intrinsic parameters are the Curie temperature TC and the density of state (DOS) for itinerant majority and minority electrons ξ(ρM/ρm), which are the eigen parameters of ferromagnetic electrodes. Others are the spin-dependent matrix-element ratio (i.e., |Td|2/|TJ|2 ) and the anisotropic-wavelength-cutoff energy ECγ of spin-wave spectrum in magnetic tunnel junction (MTJ), which are the structure parameters of an MTJ. These intrinsic parameters can be predetermined using the experimental measurement or, in principle, using the first-principle calculation method for an MTJ with the three key layers of FM/I/FM. Furthermore, a series of experimental data for an MTJ, for example, a spin-valve-type MTJ of Ta (5 nm)/Ni79Fe21(25 nm)/lr22Mn78(12 nm)/Co75Fe25(4 nm)/AI(0.8 nm)-oxide/Co75Fe25(4 nm)/Ni79Fe21(20 nm)/Ta (5 nm) in this work, can be self-consistently evaluated and explained using such concise explicit function formulations.展开更多
We investigate the resistance and magnetoresistance （MR） of an entangled single-walled carbon nanotube （SWNT） network. The temperature dependence of conductance is fitted by formula G（T） = Go exp[-（To/T）^1/2] ...We investigate the resistance and magnetoresistance （MR） of an entangled single-walled carbon nanotube （SWNT） network. The temperature dependence of conductance is fitted by formula G（T） = Go exp[-（To/T）^1/2] with To = 15.8 K at a wide temperature range from 4 K to 300K. The MR defined by [R（T, H） - R（T, 0）]/ R（T, 0） as a function of temperature and magnetic field perpendicular to the tube axis is negative at low temperatures. The MR amplitude increases as the temperature decreases at relative high temperature, but becomes decrease when temperature below 4 K. The results are explained in terms of the coherent hopping of carriers in the presence of a Coulomb gap at low temperature.展开更多
We propose in this paper that a dual waveguide coupled by a finite barrier be able to serve as an energy filter under a perpendicular magnetic field. In the waveguide direction, the conductance exhibits a periodic squ...We propose in this paper that a dual waveguide coupled by a finite barrier be able to serve as an energy filter under a perpendicular magnetic field. In the waveguide direction, the conductance exhibits a periodic square-wave pattern in which the miniband is controlled by the magnetic and potential modulation. The electrons with energies in the miniband can completely transfer along one waveguide while the other electrons undergo filtration. Compared with the coupled waveguide without magnetic modulation, the structure under magnetic field is found to be a good directional coupler. By adjusting the potential barrier and magnetic field, the electrons input from one port of waveguide can transfer to any other ports.展开更多
In this review article,we review the progress made in the past several years mainly regarding the efforts devoted to increasing the Curie temperature(T C) of(Ga,Mn)As,which is most widely considered as the prototype f...In this review article,we review the progress made in the past several years mainly regarding the efforts devoted to increasing the Curie temperature(T C) of(Ga,Mn)As,which is most widely considered as the prototype ferromagnetic semiconductor.Heavy Mn doping,nanostructure engineering and post-growth annealing which increase T C are described in detail.展开更多
We report the magnetoresistance（MR）, de Haas-van Alphen（dHvA） effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field,...We report the magnetoresistance（MR）, de Haas-van Alphen（dHvA） effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field, a metal-to-insulator-like transition in ρ（T） and a nonsaturating MR are observed at low temperatures. The dHvA oscillations reveal a small Fermi-surface pocket with a nontrivial Berry phase. The analysis of the nonlinear Hall resistivity shows that TiSi is a multiband system with low carrier densities and high mobilities. All these results unambiguously prove the existence of Dirac fermions in TiSi.展开更多
基金supported by NSF of China (Grant No. 61775241)partly by the Innovation-driven Project (Grant No. 2017CX019)the funding support from the Australian Research Council (ARC Discovery Projects, DP180102976)
文摘With a large number of researches being conducted on two?dimen?sional(2D) materials, their unique properties in optics, electrics, mechanics, and magnetics have attracted increasing attention. Accordingly, the idea of combining distinct functional 2D materials into heterostructures naturally emerged that pro?vides unprecedented platforms for exploring new physics that are not accessible in a single 2D material or 3D heterostructures. Along with the rapid development of controllable, scalable, and programmed synthesis techniques of high?quality 2D heterostructures, various heterostructure devices with extraordinary performance have been designed and fabricated, including tunneling transistors, photodetectors, and spintronic devices. In this review, we present a summary of the latest progresses in fabrications, properties, and applications of di erent types of 2D heterostruc?tures, followed by the discussions on present challenges and perspectives of further investigations.
基金supported by the National Natural Science Foundation of China(Grant No.12074425)the National Key R&D Program of China(Grant No.2019YFA0308602)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(Grant No.23XNKJ22)。
文摘We conduct a detailed examination of the magnetic and electrical transport properties in GdAlSi and SmAlGe crystals,which possess a LaPtSi-type structure(space group I4_(1)md).The magnetic susceptibility data unambiguously reveal magnetic ordering below a characteristic transition temperature(T_(N)).For GdAlSi,a hysteresis loop is observed in the magnetization and magnetoresistance curves within the ab plane when the magnetic field is applied below T_(N),which is around32 K.Notable specific heat anomalies are detected at 32 K for GdAlSi and 6 K for SmAlGe,confirming the occurrence of magnetic transitions.In addition,the extracted magnetic entropy at high temperatures is consistent with the theoretical value of Rln(2J+1) for J=7/2 in Gd^(3+) and J=5/2 in Sm^(3+),respectively.SmAlGe also exhibits Schottky-like specific heat contributions.Additionally,both GdAlSi and SmAlGe exhibit positive magnetoresistance and a normal Hall effect.
基金support from the National Natural Science Foundation of China(NSFC)under grant No.51872155 and 52025024the Beijing Nature Science Foundation(Z200007)+4 种基金the Ministry of Science and Technology of China(2021YFE0107900 and 2021YFA1400300)support from the High Magnetic Field Laboratory of Anhui Province(AHHM-FX-2021-03)the NSFC under Grant No.12104460support from the NSFC under Grant No.92163113 and No.52250418support from the National Science Foundation under Grant No.DMR1848269.
文摘Over the last few years,researches in iridates have developed into an exciting field with the discovery of numerous emergent phenomena,interesting physics,and intriguing functionalities.Among the studies,iridate-based artificial structures play a crucial role owing to their extreme flexibility and tunability in lattice symmetry,chemical composition,and crystal dimensionality.In this article,we present an overview of the recent progress regarding iridate-based artificial structures.We first explicitly introduce several essential concepts in iridates.Then,we illustrate important findings on representative SrIrO_(3)/SrTiO_(3) superlattices,heterostructures comprised of SrIrO3 and magnetic oxides,and their response to external electric-field stimuli.Finally,we comment on existing problems and promising future directions in this exciting field.
基金partially supported by the High Magnetic Field Laboratory of Anhui Province,China。
文摘We theoretically investigate the quantum interference theory of magnetotransport of the three-component or spin-1 chiral fermions, which possess two linear Dirac bands and a flat band. For isotropic scalar impurities, the correction of conductivity from the coherent backscatter and non-coherent backscatter contributions cancel out in the intravalley scattering, leading to a weak localization correction to the Drude conductivity from the intervalley scattering. For the anisotropic impurities, the above cancelation is removed, we find the approximative quantum interference conductivity in the weak anisotropy case. The contributions from the chiral anomaly and classical Lorentz force are also discussed. Our work reveals some intriguing and detectable transport signatures of the novel spin-1 chiral fermions.
基金S.Y.is supported by the National Science Foundation Division of Chemical,Bioengineering,Environmental,and Transport Systems(No.1749742)M.Y.is supported by the Department of Energy(DE-SC0014476)J.J.C.acknowledges support from the Army Research Office(No.71816-MS).
文摘Layered transition metal dichalcogenides(TMDCs)have been extensively studied owing to their unique physical and chemical properties.Weak van der Waals(vdW)interact!ons betwee n the stacki ng layers of TMDCs allow intercalati on of various species including mono vale nt alkali,divale nt alkaline earth and multivale nt metal ions,zero-vale nt transiti on metals,as well as orga nic molecules,all of which can drastically alter fun dame ntal properties of the TMDCs.The urge to understa nd the phe nomena and the desire to exploit them for applicati ons have inspired a great deal of investigations.A large portion of the mystery has been unveiled over the past decade of intense research;however,many questions remain open and require further explorations.This review is concerned with investigations on structural and electronic evolution of TMDCs drive n by electrochemically con trolled in tercalati ons.Herein,we aim to survey the rece nt adva nces and experime ntal platforms for mon itoring the in tercalati on processes in situ by utilizi ng nano devices.In additi on,several in quiries and prospects are outlined in a broader con text for future ave nues of studies.
基金supported by the National Natural Science Foundation of China(Grant Nos.U19A2093,11904002,and U2032163)the National Key Research and Development Program of China(Grant No.2021YFA1600201)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2021117)。
文摘The superconductivity and nontrivial topological electronic state are key hallmarks of topological superconductors.Here,we focus on the transport signals of possible topological surface state in the topological superconductor candidate β-PdBi_(2) nanoflake with a thickness of 21 nm.The resistance demonstrates a semiconductor-metal transition followed by an upturned behavior as the temperature decreases.A large and unsaturated longitudinal magnetoresistance(MR),accompanied by distinct Shubnikov-de Hass oscillation in Hall resistance,is observed.An analysis of Hall resistance reveals that the carriers present the characteristics of relativistic particles with small effective mass and extremely high mobility.The angle-dependent quantum oscillations demonstrate a two-dimensional Fermi surface topology.A giant anisotropic MR as large as 98%is detected when rotating the magnetic field.These results provide the possible transport signals of a nontrivial topological electronic state,establishing a further understanding of the topological properties of the low-dimensional topological superconductor candidate β-PdBi_(2).
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10774107, 10874126 and 10804080)the Doctoral Program of High Education of China (Grant No 20060285003)
文摘Simulations are performed on clusters of finite size to study the effects of size and current-path structure on magnetotransport in spatially-confined samples. Magnetotransport networks are established and calculated based on fractal structures including Koch curves and percolation backbones extracted from regular lattices. The structure pattern of clusters is shown to play an important role in the magnetotransport behaviours by affecting the magnetore- sistance fluctuations due to spin disorder in the systems of small size, which suggests the possibility of controlling the magnetotransport by the design of current-path configurations.
文摘Base optimum thickness is determined for a front illuminated bifacial silicon solar cell n<sup>+</sup>-p<span style="font-size:10px;">-</span>p<sup>+</sup> under magnetic field. From the magneto transport equation relative to excess minority carriers in the base, with specific boundary conditions, the photocurrent is obtained. From this result the expressions of the carrier’s recombination velocity at the back surface are deducted. These new expressions of recombination velocity are plotted according to the depth of the base, to deduce the optimum thickness, which will allow the production, of a high short-circuit photocurrent. Calibration relationships of optimum thickness versus magnetic field were presented according to study ranges. It is found that, applied magnetic field imposes a weak thickness material for solar cell manufacturing leading to high short-circuit current.
文摘Resistivity, magnetoresistivity and Hall effect measurements in n-type Te-doped GaSb grown by the liquid encapsuled Czochralski technique are carried out as functions of temperature （35-350 K） and magnetic field （0-1.35 T）. The power law model is used to explain the temperature-dependent resistivity. The magnetic-field-dependent data are analysed using the quantitative mobility spectrum analysis technique. The effect of individual band parameters （nL, nr, μL, μr, p and μp） on both the electron and magneto transports have been discussed. The EL - Er energy separation between the L and conduction band edges is also derived.
文摘A series of bulk polycrystalline La1-xLixMnO3 samples with x ranging from 0.1 to 0.5 was prepared by sol-gel method,X-ray diffraction patterns show that the crystal structures are single rhombohedral perorskite for the x≤0.3 sample and the impurity appears when x〉0.3.Under the same synthesized conditions,the higher Li content samples display a higher content of liquid phase content and larger mean grain sizes,which leads to the increases of the effect of the grain boundaries.The experimental results show that the change of the ferromagnetic transition temperature and the resistivity can attribute to the effect of the grain boundary and the connectivity of the inter grains as well as the ratio of Mn^3＋ to Mn^4＋.
基金Supported by the National Major Fundamental Research Program of China (Grant No G1998061412)the Foundation for Fostering Elitists of Beijing, China (Grant No 20071D1100500379)
文摘The LaMn1-xTexO3+δ (x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3+ ions are partly converted into Mn2+ and Mn4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn2+, Mn3+ and Mn4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn3+ is much larger or less than the sum of Mn2+ and Mn4+; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn3+ is close to the sum of Mn2+ and Mn4+. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism.
基金Project supported by the National Key R&D Program of China(Grant Nos.2016YFA0300904 and 2016YFA0202301)the National Natural Science Foundation of China(Grant Nos.11334011,11674366,11674368,and 11761141013)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB07010200 and XDPB06)
文摘Exchange coupling between topological insulator and ferromagnetic insulator through proximity effect is strongly attractive for both fundamental physics and technological applications. Here we report a comprehensive investigation on the growth behaviors of prototype topological insulator Bi2Se3 thin film on a single-crystalline LaCoO3 thin film on SrTiO3 substrate, which is a strain-induced ferromagnetic insulator. Different from the growth on other substrates, the Bi2Se3 films with highest quality on LaCoO3 favor a relatively low substrate temperature during growth. As a result, an inverse dependence of carrier mobility with the substrate temperature is found. Moreover, the magnetoresistance and coherence length of weak antilocalization also have a similar inverse dependence with the substrate temperature, as revealed by the magnetotransport measurements. Our experiments elucidate the special behaviors in Bi2Se3/LaCoO3 heterostructures, which provide a good platform for exploring related novel quantum phenomena, and are inspiring for device applications.
基金Project supported by the National Basic Research Program of China (Grant No.2011CB309606)
文摘Magnetotransport measurements are carried out on the A1GaN/A1N/GaN in an SiC heterostructure, which demon- strates the existence of the high-quality two-dimensional electron gas （2DGE） at the A1N/GaN interface. While the carrier concentration reaches 1.32×10^13 cm^-2 and stays relatively unchanged with the decreasing temperature, the mobility of the 2DEG increases to 1.21 × 10^4 cm2/（V.s） at 2 K. The Shubnikov-de Haas （SdH） oscillations are observed in a magnetic field as low as 2.5 T at 2 K. By the measurements and the analyses of the temperature-dependent SdH oscillations, the effective mass of the 2DEC is determined. The ratio of the transport lifetime to the quantum scattering time is 9 in our sample, indicating that small-angle scattering is predominant.
基金This work was supported by 2000 Hundred Talents Program project of Chinese Academy of Sciences and 973 project with Grant No. 2001CB610601 of PRC Ministry of Science and Technology. X.F.Han also gratefully acknowledges the partial support of K.C.Wong Edu
文摘An explicit function expression for the bias voltage or/and temperature dependences of tunnel magnetoresistance ratio and resistances were obtained with a unique set of intrinsic parameters. Two of these intrinsic parameters are the Curie temperature TC and the density of state (DOS) for itinerant majority and minority electrons ξ(ρM/ρm), which are the eigen parameters of ferromagnetic electrodes. Others are the spin-dependent matrix-element ratio (i.e., |Td|2/|TJ|2 ) and the anisotropic-wavelength-cutoff energy ECγ of spin-wave spectrum in magnetic tunnel junction (MTJ), which are the structure parameters of an MTJ. These intrinsic parameters can be predetermined using the experimental measurement or, in principle, using the first-principle calculation method for an MTJ with the three key layers of FM/I/FM. Furthermore, a series of experimental data for an MTJ, for example, a spin-valve-type MTJ of Ta (5 nm)/Ni79Fe21(25 nm)/lr22Mn78(12 nm)/Co75Fe25(4 nm)/AI(0.8 nm)-oxide/Co75Fe25(4 nm)/Ni79Fe21(20 nm)/Ta (5 nm) in this work, can be self-consistently evaluated and explained using such concise explicit function formulations.
文摘We investigate the resistance and magnetoresistance （MR） of an entangled single-walled carbon nanotube （SWNT） network. The temperature dependence of conductance is fitted by formula G（T） = Go exp[-（To/T）^1/2] with To = 15.8 K at a wide temperature range from 4 K to 300K. The MR defined by [R（T, H） - R（T, 0）]/ R（T, 0） as a function of temperature and magnetic field perpendicular to the tube axis is negative at low temperatures. The MR amplitude increases as the temperature decreases at relative high temperature, but becomes decrease when temperature below 4 K. The results are explained in terms of the coherent hopping of carriers in the presence of a Coulomb gap at low temperature.
文摘We propose in this paper that a dual waveguide coupled by a finite barrier be able to serve as an energy filter under a perpendicular magnetic field. In the waveguide direction, the conductance exhibits a periodic square-wave pattern in which the miniband is controlled by the magnetic and potential modulation. The electrons with energies in the miniband can completely transfer along one waveguide while the other electrons undergo filtration. Compared with the coupled waveguide without magnetic modulation, the structure under magnetic field is found to be a good directional coupler. By adjusting the potential barrier and magnetic field, the electrons input from one port of waveguide can transfer to any other ports.
基金supported by the National Natural Science Foundation of China (Grant Nos.60836002,11127406 and 10920101071)
文摘In this review article,we review the progress made in the past several years mainly regarding the efforts devoted to increasing the Curie temperature(T C) of(Ga,Mn)As,which is most widely considered as the prototype ferromagnetic semiconductor.Heavy Mn doping,nanostructure engineering and post-growth annealing which increase T C are described in detail.
基金Supported by the National Key Research Program of China under Grant Nos 2016YFA0401000 and 2016YFA0300604the National Basic Research Program of China under Grant No 2015CB921303+1 种基金the Strategic Priority Research Program(B)of Chinese Academy of Sciences under Grant No XDB07020100the National Natural Science Foundation of China under Grant No11874417
文摘We report the magnetoresistance（MR）, de Haas-van Alphen（dHvA） effect and Hall effect measurements on a single crystal of TiSi, which is predicted to be a nodal line semimetal. With application of a magnetic field, a metal-to-insulator-like transition in ρ（T） and a nonsaturating MR are observed at low temperatures. The dHvA oscillations reveal a small Fermi-surface pocket with a nontrivial Berry phase. The analysis of the nonlinear Hall resistivity shows that TiSi is a multiband system with low carrier densities and high mobilities. All these results unambiguously prove the existence of Dirac fermions in TiSi.
