三维的光事被联合单个横梁创造与常规 Z 扫描技术的光套住。动态轻衍射被采用评估在套住力量的最佳形成的光事的结构和质量。光事的格子常数基于布拉格和敏捷的法律被提取,证明聚苯乙烯范围在光事是将近拥挤不堪的,由把光事的衍射模...三维的光事被联合单个横梁创造与常规 Z 扫描技术的光套住。动态轻衍射被采用评估在套住力量的最佳形成的光事的结构和质量。光事的格子常数基于布拉格和敏捷的法律被提取,证明聚苯乙烯范围在光事是将近拥挤不堪的,由把光事的衍射模式与自我装配的技术制作的胶体的 photonic 晶体的作比较证实了。在光事观察的相对宽广的衍射山峰显示在它的混乱的密度在 photonic 水晶比那高。光事拥有随机的拥挤不堪的结构,这被建议而非一张脸集中了立方的。展开更多
This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal.In experiments,semiconductor...This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal.In experiments,semiconductor core-shell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated.The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence (PL) measurements.The modification of the spontaneous emission rate,which is reflected in the change of spectral shape and PL lifetime,is clearly observed.While an obvious increase in the PL lifetime is found at most wavelengths in the band gap,a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge.Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal.It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously.This finding provides a simple and effective way for improving the performance of light emitting devices.展开更多
We investigated the feasibility of obtaining large photoresponse in metal-semiconductor-metal(MSM) type single nanowire device where one contact can be blocking type. We showed that suitable modification of the blocki...We investigated the feasibility of obtaining large photoresponse in metal-semiconductor-metal(MSM) type single nanowire device where one contact can be blocking type. We showed that suitable modification of the blocking contact by deposition of a capping metal using focused electron beam(FEB) can lead to considerable enhancement of the photoresponse. The work was done in a single Cu:TCNQ nanowire device fabricated by direct growth of nanowires(NW) from pre-patterned Cu electrode which makes the contact ohmic with the other contact made from Au. Analysis of the data shows that the large photoresponse of the devices arises predominantly due to reduction of the barriers at the Au/NW blocking contact on illumination. This is caused by the diffusion of the photo generated carriers from the nanowires to the contact region. When the barrier height is further reduced by treating the contact with FEB deposited Pt, this results in a large enhancement in the device photoresponse.展开更多
一条理论途径被概括并且在这个工作采用了在外部磁场评估 ErBi 的磁电机抵抗力。计算结果和理论分析证明当一个外部磁场在 z 方向被使用时,磁电机抵抗力能由于水晶地层次上升的退化更加被减少。然而,当磁场沿着 X 轴被施加时,因为 Er...一条理论途径被概括并且在这个工作采用了在外部磁场评估 ErBi 的磁电机抵抗力。计算结果和理论分析证明当一个外部磁场在 z 方向被使用时,磁电机抵抗力能由于水晶地层次上升的退化更加被减少。然而,当磁场沿着 X 轴被施加时,因为 Er 离子和它的转变的新磁性的状态的形成,磁电机抵抗力将被增加在以内并且在这些新状态之间。展开更多
This paper systematically investigates the response of colloidal liquids containing magnetic holes of different volume densities to magnetic field by conventional transmission measurements. It finds that the enhanceme...This paper systematically investigates the response of colloidal liquids containing magnetic holes of different volume densities to magnetic field by conventional transmission measurements. It finds that the enhancement in the transmission of such a colloidal liquid under a magnetic field exhibits a strong dependence on the volume density of magnetic holes. A linear increase in the maximum enhancement factor is observed when the volume density of magnetic holes is below a critical level at which a maximum enhancement factor of ~150 is achieved in the near infrared region. Once the volume density of magnetic holes exceeds the critical level, a sharp drop of the maximum enhancement factor to ~2 is observed. After that, the maximum enhancement factor increases gradually till a large volume density of ~9%. By monitoring the arrangement of magnetic holes under a magnetic field, it reveals that the colloidal liquids can be classified into three different phases, i.e., the gas-like, liquid-like and solid-like phases, depending on the volume density of magnetic holes. The response behaviour of colloidal liquids to magnetic field is determined by the interaction between magnetic holes which is governed mainly by their volume density. A phase transition, which is manifested in the dramatic reduction in the maximum enhancement factor, is clearly observed between the liquid-like and solid-like phases. The optical switching operations for colloidal liquids in different phases are compared and the underlying physical mechanisms are discussed.展开更多
A Usov-type quantum model based on a mean-field approximation is utilized to simulate the magnetic structure of an assumed rare-earth nanoparticle consisting of an antiferromagnetic core and a paramagnetic outer shell...A Usov-type quantum model based on a mean-field approximation is utilized to simulate the magnetic structure of an assumed rare-earth nanoparticle consisting of an antiferromagnetic core and a paramagnetic outer shell.We study the magnetic properties in the presence and absence of an external magnetic field.Our simulation results show that the magnetic moments in the core region orientate antiferromagnetically in zero external magnetic field;an applied magnetic field rotates all of the magnetic moments in the paramagnetic shell completely to the field direction,and turns those in the core(which tries to maintain its original antiferromagnetic structure)towards the orientation in some degree;and the paramagnetic shell does not have a strong influence on the magnetic configuration of the core.展开更多
We have measured weak antilocalization effects, universal conductance fluctuations, and Aharonov-Bohm oscillations in the two-dimensional electron gas formed in InGaAs/AlInAs heterostructures. This system possesses st...We have measured weak antilocalization effects, universal conductance fluctuations, and Aharonov-Bohm oscillations in the two-dimensional electron gas formed in InGaAs/AlInAs heterostructures. This system possesses strong spin-orbit coupling and a high Landé factor. Phase-coherence lengths of 2 - 4 μm at 1.5 - 4.2 K are extracted from the magnetoconductance measurements. The analysis of the coherence-sensitive data reveals that the temperature dependence of the decoherence rate complies with the dephasing mechanism originating from electron-electron interactions in all three experiments. Distinct beating patterns superimposed on the Aharonov-Bohm oscillations are observed over a wide range of magnetic fields, up to 0.7 Tesla at the relatively high temperature of 1.5 K. The possibility that these beats are due to the interplay between the Aharonov-Bohm phase and the Berry one, different for electrons of opposite spins in the presence of strong spin-orbit and Zeeman interactions in ring geometries, is carefully investigated. It appears that our data are not explained by this mechanism;rather, a few geometrically-different electronic paths within the ring’s width can account for the oscillations’ modulations.展开更多
It is known that α-RuCl_(3) has been studied extensively because of its proximity to the Kitaev quantum-spin-liquid(QSL)phase and the possibility of approaching it by tuning the competing interactions.Here we present...It is known that α-RuCl_(3) has been studied extensively because of its proximity to the Kitaev quantum-spin-liquid(QSL)phase and the possibility of approaching it by tuning the competing interactions.Here we present the first polarized inelastic neutron scattering study on α-RuCl_(3) single crystals to explore the scattering continuum around the Γ point at the Brillouin zone center,which was hypothesized to be resulting from the Kitaev QSL state but without concrete evidence.With polarization analyses,we find that,while the spin-wave excitations around the Γ point vanish above the transition temperature T_(N),the pure magnetic continuous excitations around the Γ point are robust against temperature.Furthermore,by calculating the dynamical spin-spin correlation function using the cluster perturbation theory,we derive magnetic dispersion spectra based on the K-Γ model,which involves with a ferromagnetic Kitaev interaction of −7.2 meV and an off-diagonal interaction of 5.6 meV.We find this model can reproduce not only the spin-wave excitation spectra around the Γ point,but also the non-spin-wave continuous magnetic excitations around the Γ point.These results provide evidence for the existence of fractional excitations around the Γ point originating from the Kitaev QSL state,and further support the validity of the K-Γ model as the effective minimal spin model to describe α-RuCl_(3).展开更多
We present a study of 2D Skyrmions under rotation. The purpose of this study is to establish the result of the rotation on the stability of 2D Skyrmions. Usually the 2D skyrmions are metastable unless the underlying g...We present a study of 2D Skyrmions under rotation. The purpose of this study is to establish the result of the rotation on the stability of 2D Skyrmions. Usually the 2D skyrmions are metastable unless the underlying geometry introduces a characteristic length or e.g. magnetic fifield is present in the problem. We have used a previous study of the rotating plane which proves the appearance of curvature as a result of the rotation. The curvature of the rotating disk introduces length and plays here the role of strength of the angular momentum of the field. We have shown that this additional length scale introduced by the curvature stabilises the 2D Skyrnions under展开更多
Purpose This study aims to create a new tool for fast computer simulations allowing one to design advanced electromagnetic calorimeters with the required properties.The application must calculate the calorimeter effic...Purpose This study aims to create a new tool for fast computer simulations allowing one to design advanced electromagnetic calorimeters with the required properties.The application must calculate the calorimeter efficiency and measure the particles'energies,momenta and interaction time to detect the particles.This application should become the basis for a new technology of positron emission tomography.Methods To solve the problem,a new C++application based on Geant4 simulation toolkit has been developed.To monitor the response of calorimeters to different types of primary particles,we used different auxiliary Geant4 classes.In addition,we compare the simulation results for the detectors of three different setups,taking into account the detection of both electrons and gamma-quanta,and analyze their efficiency.To evaluate the capability of calorimeters to work under radiation load,we use an experimentally measured transmission function of radiation-damaged PbF_(2).Results Three calorimeter setups exploiting PbF_(2)were simulated with a new C++application based on Geant4.We showed that such type of calorimeter has an energy resolution of 4.1%√E^(e+)[GeV]and good linearity of response for GeV positrons measurements.The efficiency of such structures is found to be approximately 20%for gamma photons’detection.The multilayered structure based on gamma-quanta detection has been proven to be more efficient.It was shown that for the total ionizing dose of 30 krad the Cherenkov light yield decreases by up to two times for 14 cm long PbF_(2)crystals,while for the shorter ones(2.5 and 1.5 cm)this effect is almost negligible.Conclusions We present a new user application in Geant4 for fast simulation of complex structures designed for detection of different high-energy neutral and charged particles.Simulation of calorimeter interaction with 10^(3) of 3 GeV positrons takes 20 min on usual laptop,while for 105511 keV gamma photons it takes 1 min on average.This application allows one to evaluate the efficiency of electromagnetic calorimeters exploiting lead fluoride crystals.Our results pave the way for advanced particle energy measurements,including those used in rapidly developing medical applications such as positron emission tomography,single-photon emission computed tomography etc.展开更多
Bi_(2)SeO_(5)是一种具有优异电绝缘性能的范德华(vdW)层状介电材料,引起了极大关注.然而,目前关于Bi_(2)SeO_(5)的研究主要停留在实验层面,仍然缺乏对其原子级薄膜的介电性能的相关理论认识.本文通过第一性原理计算确定了Bi_(2)SeO_(5...Bi_(2)SeO_(5)是一种具有优异电绝缘性能的范德华(vdW)层状介电材料,引起了极大关注.然而,目前关于Bi_(2)SeO_(5)的研究主要停留在实验层面,仍然缺乏对其原子级薄膜的介电性能的相关理论认识.本文通过第一性原理计算确定了Bi_(2)SeO_(5)的介电性能,发现其块体、双层和单层均具有超高平均介电常数(εr>20).研究表明,单层Bi_(2)SeO_(5)与双层Bi_(2)O_(2)Se之间的导带和价带能量偏移量均大于1 eV,表明单层Bi_(2)SeO_(5)依然可作为原子薄Bi_(2)O_(2)Se的良好介电层.此外,不同于h-BN或其他2D vdW绝缘体,Bi_(2)SeO_(5)的εr由其离子部分主导,且随着厚度的减小几乎保持不变.计算发现,单层Bi_(2)SeO_(5)的等效氧化层厚度可薄至0.3 n m,且单层Bi_(2)SeO_(5)在拉伸或压缩应变达到6%时均能保持高介电常数,这极大地促进了它与各种二维半导体的集成.本工作证明单层Bi_(2)SeO_(5)可以作为高性能二维电子器件良好的封装和介电层.展开更多
Vortices and bound states offer an effective means of comprehending the electronic properties of superconductors.Recently,surface-dependent vortex core states have been observed in the newly discovered kagome supercon...Vortices and bound states offer an effective means of comprehending the electronic properties of superconductors.Recently,surface-dependent vortex core states have been observed in the newly discovered kagome superconductors CsV_(3)Sb_(5).Although the spatial distribution of the sharp zero energy conductance peak appears similar to Majorana bound states arising from the superconducting Dirac surface states,its origin remains elusive.In this study,we present observations of tunable vortex bound states(VBSs)in two chemically-doped kagome superconductors Cs(V_(1-x)Tr_(x))_(3)Sb_(5)(Tr=Ta or Ti),using low-temperature scanning tunneling microscopy/spectroscopy.The CsV_(3)Sb_(5)-derived kagome superconductors exhibit full-gap-pairing superconductivity accompanied by the absence of long-range charge orders,in contrast to pristine CsV_(3)Sb_(5).Zero-energy conductance maps demonstrate a field-driven continuous reorientation transition of the vortex lattice,suggesting multiband superconductivity.The Ta-doped CsV_(3)Sb_(5)displays the conventional cross-shaped spatial evolution of Caroli-de Gennes-Matricon bound states,while the Tidoped CsV_(3)Sb_(5)exhibits a sharp,non-split zero-bias conductance peak(ZBCP)that persists over a long distance across the vortex.The spatial evolution of the non-split ZBCP is robust against surface effects and external magnetic field but is related to the doping concentrations.Our study reveals the tunable VBSs in multiband chemically-doped CsV_(3)Sb_(5)system and offers fresh insights into previously reported Y-shaped ZBCP in a non-quantum-limit condition at the surface of kagome superconductor.展开更多
We investigated metal-organic vapor phase epitaxy grown(InGa)(AsSb)/GaAs/GaP Stranski–Krastanov quantum dots(QDs)with potential applications in QD-Flash memories by cross-sectional scanning tunneling microscopy(X-STM...We investigated metal-organic vapor phase epitaxy grown(InGa)(AsSb)/GaAs/GaP Stranski–Krastanov quantum dots(QDs)with potential applications in QD-Flash memories by cross-sectional scanning tunneling microscopy(X-STM)and atom probe tomography(APT).The combination of X-STM and APT is a very powerful approach to study semiconductor heterostructures with atomic resolution,which provides detailed structural and compositional information on the system.The rather small QDs are found to be of truncated pyramid shape with a very small top facet and occur in our sample with a very high density of∼4×10^(11) cm^(−2).APT experiments revealed that the QDs are GaAs rich with smaller amounts of In and Sb.Finite element(FE)simulations are performed using structural data from X-STM to calculate the lattice constant and the outward relaxation of the cleaved surface.The composition of the QDs is estimated by combining the results from X-STM and the FE simulations,yielding∼In_(x)Ga_(1−x)As_(1−y)Sb_(y),where x=0.25–0.30 and y=0.10–0.15.Noticeably,the reported composition is in good agreement with the experimental results obtained by APT,previous optical,electrical,and theoretical analysis carried out on this material system.This confirms that the InGaSb and GaAs layers involved in the QD formation have strongly intermixed.A detailed analysis of the QD capping layer shows the segregation of Sb and In from the QD layer,where both APT and X-STM show that the Sb mainly resides outside the QDs proving that Sb has mainly acted as a surfactant during the dot formation.Our structural and compositional analysis provides a valuable insight into this novel QD system and a path for further growth optimization to improve the storage time of the QD-Flash memory devices.展开更多
A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifluoroethylene)copolymer P(VDFTrFE)and ferroelectric ceramics of barium lead zirconate titanate(BPZT)solid solution is pre...A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifluoroethylene)copolymer P(VDFTrFE)and ferroelectric ceramics of barium lead zirconate titanate(BPZT)solid solution is presented in this work.The composite films containing up to 50 vol.%of BPZT grains with size1m were prepared by the solvent cast method.Frequency dependences of real and imaginary components of the complex permittivity were determined.The concentration dependence of the dielectric constant was discussed.展开更多
Electronic properties of selected quantum dot(QD)systems are surveyed based on the multi-band k·p method,which we benchmark by direct comparison to the empirical tight-binding algorithm,and we also discuss the ne...Electronic properties of selected quantum dot(QD)systems are surveyed based on the multi-band k·p method,which we benchmark by direct comparison to the empirical tight-binding algorithm,and we also discuss the newly developed"linear combination of quantum dot orbitals"method.Furthermore,we focus on two major complexes:First,the role of antimony incorporation in InGaAs/GaAs submonolayer QDs and In1−xGax AsySb1−y/GaP QDs,and second,the theory of QD-based quantum cascade lasers and the related prospect of room temperature lasing.展开更多
Rietveld refinement analysis indicates that A_(2)ErTaO_(6)(A=Sr^(+2),Ca^(+2)ceramics prepared by a solid-state route are crystallized in monoclinic perovskite phase with space group P21=n.Raman scattering and infrared...Rietveld refinement analysis indicates that A_(2)ErTaO_(6)(A=Sr^(+2),Ca^(+2)ceramics prepared by a solid-state route are crystallized in monoclinic perovskite phase with space group P21=n.Raman scattering and infrared spectroscopy are used to investigate the structure and phonon modes of the samples.Using Lorentzian lines,we have fitted the Raman spectra and the major Raman modes are assigned.Phonon vibrational frequency is modulated with the A-site cationic change.Impedance spectra of the samples over the frequency range of 100 Hz–1.1 MHz are investigated at different temperatures from 303 K to 573 K.Cole–Cole relaxation of dielectric constant is modified with the electrical conduction parameter to describe the temperature dependence of dielectric constant.The frequency-dependent conductivity spectra follow the double power-law.展开更多
In this work,the study of dielectric properties of composite structures on the base of poly(vinylidene fluoride-triflouroethylene)copolymer P(VDF-TrFE)and porous aluminum oxide layers produced by the melt-impregnation...In this work,the study of dielectric properties of composite structures on the base of poly(vinylidene fluoride-triflouroethylene)copolymer P(VDF-TrFE)and porous aluminum oxide layers produced by the melt-impregnation is presented.Frequency dependences of dielectric characteristics of the composite samples were determined.The dielectric dispersion and ferroelectric switching processes in the composite structures were discussed.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 10674051 and 10811120010, and the Program for Innowtive Research Team of the Higher Education in Guangdong under Grant No 06CXTD005.
文摘三维的光事被联合单个横梁创造与常规 Z 扫描技术的光套住。动态轻衍射被采用评估在套住力量的最佳形成的光事的结构和质量。光事的格子常数基于布拉格和敏捷的法律被提取,证明聚苯乙烯范围在光事是将近拥挤不堪的,由把光事的衍射模式与自我装配的技术制作的胶体的 photonic 晶体的作比较证实了。在光事观察的相对宽广的衍射山峰显示在它的混乱的密度在 photonic 水晶比那高。光事拥有随机的拥挤不堪的结构,这被建议而非一张脸集中了立方的。
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10974060 and 10774050)the Program for Innovative Research Team of the Higher Education in Guangdong,China (Grant No. 06CXTD005)
文摘This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal.In experiments,semiconductor core-shell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated.The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence (PL) measurements.The modification of the spontaneous emission rate,which is reflected in the change of spectral shape and PL lifetime,is clearly observed.While an obvious increase in the PL lifetime is found at most wavelengths in the band gap,a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge.Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal.It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously.This finding provides a simple and effective way for improving the performance of light emitting devices.
基金Nanomission,Department of Science and Technology,Govt. of India for financial support as sponsored project:Theme Unit of Excellence in Nanodevice Technology
文摘We investigated the feasibility of obtaining large photoresponse in metal-semiconductor-metal(MSM) type single nanowire device where one contact can be blocking type. We showed that suitable modification of the blocking contact by deposition of a capping metal using focused electron beam(FEB) can lead to considerable enhancement of the photoresponse. The work was done in a single Cu:TCNQ nanowire device fabricated by direct growth of nanowires(NW) from pre-patterned Cu electrode which makes the contact ohmic with the other contact made from Au. Analysis of the data shows that the large photoresponse of the devices arises predominantly due to reduction of the barriers at the Au/NW blocking contact on illumination. This is caused by the diffusion of the photo generated carriers from the nanowires to the contact region. When the barrier height is further reduced by treating the contact with FEB deposited Pt, this results in a large enhancement in the device photoresponse.
基金Supported by the Natural Science Foundation of Jiangsu Province under Grant No BK2008438, and the Ministry of Education of the Czech Republic under Grant No MSM-0021620834.
文摘我们雇用一个二离子的模特儿与吝啬地的理论计算 TbNi2B2C 的自发的磁化和危险性,并且为 N 耀导出一个分析公式吗??
基金Supported by the Natural Science Foundation of Jiangsu Province under Grant No BK2008438, and the Research Plan MSM of the Ministry of Education of the Czech Republic under Grant No 0021620834.
文摘一条理论途径被概括并且在这个工作采用了在外部磁场评估 ErBi 的磁电机抵抗力。计算结果和理论分析证明当一个外部磁场在 z 方向被使用时,磁电机抵抗力能由于水晶地层次上升的退化更加被减少。然而,当磁场沿着 X 轴被施加时,因为 Er 离子和它的转变的新磁性的状态的形成,磁电机抵抗力将被增加在以内并且在这些新状态之间。
基金Supported by the Natural Science Foundation of Jiangsu Province under Grant No BK2008438, and the Ministry of Education of the Czech Republic under Grant No MSM 0021620834.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10974060 and 10774050)the Program for Innovative Research Team of the Higher Education of Guangdong Province of China (Grant No. 06CXTD005)President Foundation of South China Agricultural University (Grant No. 2009K018)
文摘This paper systematically investigates the response of colloidal liquids containing magnetic holes of different volume densities to magnetic field by conventional transmission measurements. It finds that the enhancement in the transmission of such a colloidal liquid under a magnetic field exhibits a strong dependence on the volume density of magnetic holes. A linear increase in the maximum enhancement factor is observed when the volume density of magnetic holes is below a critical level at which a maximum enhancement factor of ~150 is achieved in the near infrared region. Once the volume density of magnetic holes exceeds the critical level, a sharp drop of the maximum enhancement factor to ~2 is observed. After that, the maximum enhancement factor increases gradually till a large volume density of ~9%. By monitoring the arrangement of magnetic holes under a magnetic field, it reveals that the colloidal liquids can be classified into three different phases, i.e., the gas-like, liquid-like and solid-like phases, depending on the volume density of magnetic holes. The response behaviour of colloidal liquids to magnetic field is determined by the interaction between magnetic holes which is governed mainly by their volume density. A phase transition, which is manifested in the dramatic reduction in the maximum enhancement factor, is clearly observed between the liquid-like and solid-like phases. The optical switching operations for colloidal liquids in different phases are compared and the underlying physical mechanisms are discussed.
基金by the Natural Science Foundation of Jiangsu Province under Grant No BK2008438the Ministry of Education of the Czech Republic under Grant No MSM 0021620834.
文摘A Usov-type quantum model based on a mean-field approximation is utilized to simulate the magnetic structure of an assumed rare-earth nanoparticle consisting of an antiferromagnetic core and a paramagnetic outer shell.We study the magnetic properties in the presence and absence of an external magnetic field.Our simulation results show that the magnetic moments in the core region orientate antiferromagnetically in zero external magnetic field;an applied magnetic field rotates all of the magnetic moments in the paramagnetic shell completely to the field direction,and turns those in the core(which tries to maintain its original antiferromagnetic structure)towards the orientation in some degree;and the paramagnetic shell does not have a strong influence on the magnetic configuration of the core.
文摘We have measured weak antilocalization effects, universal conductance fluctuations, and Aharonov-Bohm oscillations in the two-dimensional electron gas formed in InGaAs/AlInAs heterostructures. This system possesses strong spin-orbit coupling and a high Landé factor. Phase-coherence lengths of 2 - 4 μm at 1.5 - 4.2 K are extracted from the magnetoconductance measurements. The analysis of the coherence-sensitive data reveals that the temperature dependence of the decoherence rate complies with the dephasing mechanism originating from electron-electron interactions in all three experiments. Distinct beating patterns superimposed on the Aharonov-Bohm oscillations are observed over a wide range of magnetic fields, up to 0.7 Tesla at the relatively high temperature of 1.5 K. The possibility that these beats are due to the interplay between the Aharonov-Bohm phase and the Berry one, different for electrons of opposite spins in the presence of strong spin-orbit and Zeeman interactions in ring geometries, is carefully investigated. It appears that our data are not explained by this mechanism;rather, a few geometrically-different electronic paths within the ring’s width can account for the oscillations’ modulations.
基金supported by National Key Research and Development Program of China(Grant No.2021YFA1400400)the National Natural Science Foundation of China(Grant Nos.11822405,12074174,12074175,11774152,11904170,12004249,12004251,and 12004191)+3 种基金the Natural Science Foundation of Jiangsu Province(Grant Nos.BK20180006,BK20190436 and BK20200738)the Shanghai Sailing Program(Grant Nos.20YF1430600 and21YF1429200)the Fundamental Research Funds for the Central Universities(Grant No.020414380183)the Office of International Cooperation and Exchanges of Nanjing University。
文摘It is known that α-RuCl_(3) has been studied extensively because of its proximity to the Kitaev quantum-spin-liquid(QSL)phase and the possibility of approaching it by tuning the competing interactions.Here we present the first polarized inelastic neutron scattering study on α-RuCl_(3) single crystals to explore the scattering continuum around the Γ point at the Brillouin zone center,which was hypothesized to be resulting from the Kitaev QSL state but without concrete evidence.With polarization analyses,we find that,while the spin-wave excitations around the Γ point vanish above the transition temperature T_(N),the pure magnetic continuous excitations around the Γ point are robust against temperature.Furthermore,by calculating the dynamical spin-spin correlation function using the cluster perturbation theory,we derive magnetic dispersion spectra based on the K-Γ model,which involves with a ferromagnetic Kitaev interaction of −7.2 meV and an off-diagonal interaction of 5.6 meV.We find this model can reproduce not only the spin-wave excitation spectra around the Γ point,but also the non-spin-wave continuous magnetic excitations around the Γ point.These results provide evidence for the existence of fractional excitations around the Γ point originating from the Kitaev QSL state,and further support the validity of the K-Γ model as the effective minimal spin model to describe α-RuCl_(3).
文摘We present a study of 2D Skyrmions under rotation. The purpose of this study is to establish the result of the rotation on the stability of 2D Skyrmions. Usually the 2D skyrmions are metastable unless the underlying geometry introduces a characteristic length or e.g. magnetic fifield is present in the problem. We have used a previous study of the rotating plane which proves the appearance of curvature as a result of the rotation. The curvature of the rotating disk introduces length and plays here the role of strength of the angular momentum of the field. We have shown that this additional length scale introduced by the curvature stabilises the 2D Skyrnions under
基金This work was supported by the Ministry of Science and Higher Education of the Russian Federation,projects№FZWG-2020-0032(2019-1569)№FSWU-2023-0075.
文摘Purpose This study aims to create a new tool for fast computer simulations allowing one to design advanced electromagnetic calorimeters with the required properties.The application must calculate the calorimeter efficiency and measure the particles'energies,momenta and interaction time to detect the particles.This application should become the basis for a new technology of positron emission tomography.Methods To solve the problem,a new C++application based on Geant4 simulation toolkit has been developed.To monitor the response of calorimeters to different types of primary particles,we used different auxiliary Geant4 classes.In addition,we compare the simulation results for the detectors of three different setups,taking into account the detection of both electrons and gamma-quanta,and analyze their efficiency.To evaluate the capability of calorimeters to work under radiation load,we use an experimentally measured transmission function of radiation-damaged PbF_(2).Results Three calorimeter setups exploiting PbF_(2)were simulated with a new C++application based on Geant4.We showed that such type of calorimeter has an energy resolution of 4.1%√E^(e+)[GeV]and good linearity of response for GeV positrons measurements.The efficiency of such structures is found to be approximately 20%for gamma photons’detection.The multilayered structure based on gamma-quanta detection has been proven to be more efficient.It was shown that for the total ionizing dose of 30 krad the Cherenkov light yield decreases by up to two times for 14 cm long PbF_(2)crystals,while for the shorter ones(2.5 and 1.5 cm)this effect is almost negligible.Conclusions We present a new user application in Geant4 for fast simulation of complex structures designed for detection of different high-energy neutral and charged particles.Simulation of calorimeter interaction with 10^(3) of 3 GeV positrons takes 20 min on usual laptop,while for 105511 keV gamma photons it takes 1 min on average.This application allows one to evaluate the efficiency of electromagnetic calorimeters exploiting lead fluoride crystals.Our results pave the way for advanced particle energy measurements,including those used in rapidly developing medical applications such as positron emission tomography,single-photon emission computed tomography etc.
基金supported by the National Natural Science Foundation of China (92064005, 12104072, and 12147102)Chongqing Research Program of Basic Research and Frontier Technology,China (cstc2021jcyj-msxm X0640)the Fundamental Research Funds for the Central Universities of China (2023CDJXY-048)。
文摘Bi_(2)SeO_(5)是一种具有优异电绝缘性能的范德华(vdW)层状介电材料,引起了极大关注.然而,目前关于Bi_(2)SeO_(5)的研究主要停留在实验层面,仍然缺乏对其原子级薄膜的介电性能的相关理论认识.本文通过第一性原理计算确定了Bi_(2)SeO_(5)的介电性能,发现其块体、双层和单层均具有超高平均介电常数(εr>20).研究表明,单层Bi_(2)SeO_(5)与双层Bi_(2)O_(2)Se之间的导带和价带能量偏移量均大于1 eV,表明单层Bi_(2)SeO_(5)依然可作为原子薄Bi_(2)O_(2)Se的良好介电层.此外,不同于h-BN或其他2D vdW绝缘体,Bi_(2)SeO_(5)的εr由其离子部分主导,且随着厚度的减小几乎保持不变.计算发现,单层Bi_(2)SeO_(5)的等效氧化层厚度可薄至0.3 n m,且单层Bi_(2)SeO_(5)在拉伸或压缩应变达到6%时均能保持高介电常数,这极大地促进了它与各种二维半导体的集成.本工作证明单层Bi_(2)SeO_(5)可以作为高性能二维电子器件良好的封装和介电层.
基金supported by the National Natural Science Foundation of China(61888102,52022105,92065109,and 12174428)the National Key Research and Development Projects of China(2022YFA1204100,2018YFA0305800,2019YFA0308500,2020YFA0308800,and 2022YFA1403400)+4 种基金the CAS Project for Young Scientists in Basic Research(YSBR-003 and 2022YSBR-048)the Innovation Program of Quantum Science and Technology(2021ZD0302700)the financial support from the European Research Council(ERC Consolidator Grant “Nonlinear Topo”,No.815869)ISF-Singapore-Israel Research Grant(3520/20)supported by the US DOE,Basic Energy Sciences(DE-FG02-99ER45747)。
文摘Vortices and bound states offer an effective means of comprehending the electronic properties of superconductors.Recently,surface-dependent vortex core states have been observed in the newly discovered kagome superconductors CsV_(3)Sb_(5).Although the spatial distribution of the sharp zero energy conductance peak appears similar to Majorana bound states arising from the superconducting Dirac surface states,its origin remains elusive.In this study,we present observations of tunable vortex bound states(VBSs)in two chemically-doped kagome superconductors Cs(V_(1-x)Tr_(x))_(3)Sb_(5)(Tr=Ta or Ti),using low-temperature scanning tunneling microscopy/spectroscopy.The CsV_(3)Sb_(5)-derived kagome superconductors exhibit full-gap-pairing superconductivity accompanied by the absence of long-range charge orders,in contrast to pristine CsV_(3)Sb_(5).Zero-energy conductance maps demonstrate a field-driven continuous reorientation transition of the vortex lattice,suggesting multiband superconductivity.The Ta-doped CsV_(3)Sb_(5)displays the conventional cross-shaped spatial evolution of Caroli-de Gennes-Matricon bound states,while the Tidoped CsV_(3)Sb_(5)exhibits a sharp,non-split zero-bias conductance peak(ZBCP)that persists over a long distance across the vortex.The spatial evolution of the non-split ZBCP is robust against surface effects and external magnetic field but is related to the doping concentrations.Our study reveals the tunable VBSs in multiband chemically-doped CsV_(3)Sb_(5)system and offers fresh insights into previously reported Y-shaped ZBCP in a non-quantum-limit condition at the surface of kagome superconductor.
文摘We investigated metal-organic vapor phase epitaxy grown(InGa)(AsSb)/GaAs/GaP Stranski–Krastanov quantum dots(QDs)with potential applications in QD-Flash memories by cross-sectional scanning tunneling microscopy(X-STM)and atom probe tomography(APT).The combination of X-STM and APT is a very powerful approach to study semiconductor heterostructures with atomic resolution,which provides detailed structural and compositional information on the system.The rather small QDs are found to be of truncated pyramid shape with a very small top facet and occur in our sample with a very high density of∼4×10^(11) cm^(−2).APT experiments revealed that the QDs are GaAs rich with smaller amounts of In and Sb.Finite element(FE)simulations are performed using structural data from X-STM to calculate the lattice constant and the outward relaxation of the cleaved surface.The composition of the QDs is estimated by combining the results from X-STM and the FE simulations,yielding∼In_(x)Ga_(1−x)As_(1−y)Sb_(y),where x=0.25–0.30 and y=0.10–0.15.Noticeably,the reported composition is in good agreement with the experimental results obtained by APT,previous optical,electrical,and theoretical analysis carried out on this material system.This confirms that the InGaSb and GaAs layers involved in the QD formation have strongly intermixed.A detailed analysis of the QD capping layer shows the segregation of Sb and In from the QD layer,where both APT and X-STM show that the Sb mainly resides outside the QDs proving that Sb has mainly acted as a surfactant during the dot formation.Our structural and compositional analysis provides a valuable insight into this novel QD system and a path for further growth optimization to improve the storage time of the QD-Flash memory devices.
基金supported by the Russian Scientific Foundation(Grant N 15-19-00138).
文摘A study of dielectric properties of composite films on the base of poly(vinylidene fluoride-trifluoroethylene)copolymer P(VDFTrFE)and ferroelectric ceramics of barium lead zirconate titanate(BPZT)solid solution is presented in this work.The composite films containing up to 50 vol.%of BPZT grains with size1m were prepared by the solvent cast method.Frequency dependences of real and imaginary components of the complex permittivity were determined.The concentration dependence of the dielectric constant was discussed.
文摘Electronic properties of selected quantum dot(QD)systems are surveyed based on the multi-band k·p method,which we benchmark by direct comparison to the empirical tight-binding algorithm,and we also discuss the newly developed"linear combination of quantum dot orbitals"method.Furthermore,we focus on two major complexes:First,the role of antimony incorporation in InGaAs/GaAs submonolayer QDs and In1−xGax AsySb1−y/GaP QDs,and second,the theory of QD-based quantum cascade lasers and the related prospect of room temperature lasing.
基金the University Grants Commission(UGC)for award of Teacher Fellowship[No.F.TF.WB-010-02/13-14(ERO)]under the College Faculty Development Programme.Alo Dutta thanks the Department of Science and Technology of India for providing the finan-cial support through DST Fast Track Project under the Grant No.SR/FTP/PS-175/2013.
文摘Rietveld refinement analysis indicates that A_(2)ErTaO_(6)(A=Sr^(+2),Ca^(+2)ceramics prepared by a solid-state route are crystallized in monoclinic perovskite phase with space group P21=n.Raman scattering and infrared spectroscopy are used to investigate the structure and phonon modes of the samples.Using Lorentzian lines,we have fitted the Raman spectra and the major Raman modes are assigned.Phonon vibrational frequency is modulated with the A-site cationic change.Impedance spectra of the samples over the frequency range of 100 Hz–1.1 MHz are investigated at different temperatures from 303 K to 573 K.Cole–Cole relaxation of dielectric constant is modified with the electrical conduction parameter to describe the temperature dependence of dielectric constant.The frequency-dependent conductivity spectra follow the double power-law.
基金supported by the Ministry of Education and Science of Russian Federation(Unique project identifier RFMEFI57517X0129).
文摘In this work,the study of dielectric properties of composite structures on the base of poly(vinylidene fluoride-triflouroethylene)copolymer P(VDF-TrFE)and porous aluminum oxide layers produced by the melt-impregnation is presented.Frequency dependences of dielectric characteristics of the composite samples were determined.The dielectric dispersion and ferroelectric switching processes in the composite structures were discussed.