分类: 电子与通信技术 >> 电子技术 分类: 工程与技术科学 >> 仪器仪表技术 分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2024-05-06
摘要: In this work, we design and fabricate the transimpedance Amplifier (TIA) following the design mentioned in Ref. cite{Liang2024}. In the TIA, the preamplifier (Pre-Amp) is made of a junction field effect transistor (JFET) that can work at 77 K. The post-amplifier is made of an operational amplifier (OPA). Cascade Pre-Amp and Post-Amp to form the inverting-amplifier (Inv-Amp). The gain-bandwidth product of Inv-Amp with the gain about 50,000 is higher than 10 GHz. With a 1.13 Gohm feedback network, the gain of TIA is 1.13 Gohm and its bandwidth is about 97 kHz. The equivalent input noise voltage power spectral density of TIA is not more than 9 (nV)2/Hz at 10 kHz and 4 (nV)2/Hz at 50kHz, and its equivalent input noise current power spectral density is about 26 (fA)2/Hz at 10 kHz and 240(fA)2/Hz at 50 kHz. The measured transport performances and noise performances of TIA are consistent with the simulations and calculations, verifying the feasibility for the design of low-noise large-bandwidth TIA proposed in Ref. 1 . And, TIA with various performances that meet various needs can be designed according to the design methods in Ref. 1,2 . With the same gain, the bandwidth of the TIA in this work is much larger than the present TIA and its noises are much lower than those of present ones. The TIA in this work is perfect for the cryogenic STM working at 77 K (i.e. liquid nitrogen temperature).
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2024-04-17
摘要: The identification of new materials with superconducting properties is the pursuit in the realm of superconductivity research. Here, excitedly, we show that the simplest salt daily used can be made a superconductor at normal pressure only by adjusting its stoichiometry of Na and Cl as Na3Cl at normal pressure based on first-principles calculations. This bulk stable abnormal Na-Cl stoichiometric crystal of 3:1, the first ‘magic’ ratio, includes metallic (Na) atoms in the core as well as hybridization of ionic and metallic bonding, facilitating the electron-phonon-coupling for superconductivity with a critical temperature Tc of 0.13 K. The flat bands and van Hove singularities near the Fermi level produce large densities of states, similar to H3S and LaH10, which is beneficial for the emergence of superconductivity. The crystal composed of with abnormal Na-Cl magic stoichiometry is a precisely tunable, purely sodium and chloride-based, three-dimensional bulk superconductor, which is therefore an ideal material for designing and understanding abnormal stoichiometric crystals. The methodology of constructing this bulk abnormal crystal may be general to almost all elements, which could lead to insights into the physics of other conventional superconductors and even high-critical-temperature superconductors.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2024-03-26
摘要: Under typical circumstances, it is commonly believed that solutions carrying a single type of charge are either non-existent or unstable. We have investigated the principles of high-concentration charged solution preparation techniques, employing methods such as electrostatic attraction, gravity separation, positive feedback, and self-powered mechanisms to effectively separate anions and cations in solution. Through electrostatic repulsion and the use of electrostatic separation networks, the partition of homoelectric ions has been achieved. Through water and electric separation, the capability for sustained accumulation of single-charge species has been attained, thus overcoming application bottlenecks and establishing evidence for the existence of charged solutions. We have proposed voltage limits and predicted phenomena such as electrostatic boiling, topological ice crystals, and strange ice crystals, thereby opening new perspectives and possibilities for enriching the understanding and research of electrostatics and electrochemistry. The introduction of the high-concentration charged solution and its controllable preparation are expected to facilitate or pioneer research in various fields including seawater desalination, wastewater treatment, hydrovoltaic power generation, and topological ice crystals, etc. This advancement holds the potential to rectify relevant discussions in textbooks. Implementing the dual electrostatic method for self-powered desalination and purification, coupled with wind, solar, and pumped hydro storage technologies, can aid in mitigating the intermittency and waste of wind and solar power, thus advancing the cause of seawater for land.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2024-01-20
摘要: Constructing models to discover physics underlying magnanimous data is a traditional strategy in data mining which has been proved to be powerful and successful. In this work, a multi-optimized recurrent neural network (MRNN) is utilized to predict the dynamics of photosynthetic excitation energy transfer (EET) in a light-harvesting complex. The original data set produced by the master equation were trained to forecast the EET evolution. An agreement between our prediction and the theoretical deduction with an accuracy of over 99.26 % is found, showing the validity of the proposed MRNN. A time-segment polynomial fitting multiplied by a unit step function results in a striking consistence with analytical formulations for the photosynthetic EET. The work sets up a precedent for accurate EET prediction from large data set by establishing analytical descriptions for physics hidden behind, through minimizing the processing cost during the evolution of week-coupling EET.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2022-12-09
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2022-10-21
摘要: We illustrate the microscopic quantum picture of superfluid $^4$He with the help ofrevealing a hidden property of its many-body levels. We show that, below thetransition point, the low-lying levels of the system form a grouping structure with eachlevel belonging to one specific group only. In a superflow state or a static state, the systemestablishes a group-specific thermal equilibrium with its environment and the levels of aninitially-occupied group shall be thermally distributed. The other initially-unoccupied groupsof levels remain unoccupied, due to the fact that inter-group transitions are prohibited.The macroscopically observable physical quantities of the system, such as superflowvelocity and thermal energy density, are determined statistically by the thermaldistribution of the occupied group(s). We further show that thermalenergy of a superflow has an unusual flow velocity dependence: the largerthe velocity is, the smaller the thermal energy. This velocity dependence isresponsible for several intriguing phenomena of the system, such as themechano-caloric effect and the fountain effect, which demonstrate afundamental coupling between the thermal motion of the system and itshydrodynamic motion. We report an experimental observation of a counter-intuitiveself-heating effect of $^4$He superflows, which confirms that a $^4$He superflowcarries significant thermal energy depending on its velocity.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2022-09-06
摘要: 基于微磁学模拟结果,发现由于单根纳米线两端处磁矩矢量方向与极化电流密度(J)方向的不一致,导致电子的自旋转移力矩(STT)只能作用于纳米线两端的磁矩。通过提高极化电流的自旋极化率(P),这个简化模型的微波磁谱中处在18 GHz的微波磁损耗可以得到明显的抑制,同时发现与微波损耗对应的自然共振频率大小却不受STT影响。在STT效应作用下,负的磁导率虚部也是可实现的。另外,模拟结果表明通过提高STT效应中非绝热效应项中的值,18GHz处的微波磁损耗可以得到显著的增强。基于STT效应中不同力矩的来源对磁化强度进动过程的有效阻尼常数(ɑe)的影响,上述的结果可以得到合理的解释:绝热力矩能降低ɑe数值,因而能抑制微波磁损耗的大小;非绝热力矩能提高ɑe数值,因而能增强微波磁损耗。我们的研究结果展示了一个创新性的、能主动地调控微波磁损耗的方法。
分类: 计算机科学 >> 计算机科学技术其他学科 分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2022-08-15
摘要: 随着高性能计算体系结构的发展,软件与硬件都具有了多层的并行结构。当不同纵向层级与横向分组的计算任务被划分到不同节点的不同处理器时,具有非常多的分配对应方式。用户越来越难以获取最佳的计算并行参数与硬件资源使用量。我们研究了一种优化方法,可以帮助用户自动化的确定最佳的应用并行参数与硬件使用量,使其可以高效率地扩展到大规模计算。此外,我们提出了一种将该优化方法与作业调度系统深度融合的方案,并获得了很好的应用效果。
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2022-04-30
摘要: Strain engineeringof 2D materials is capable of tuning the electrical and optical properties of the materialswithout introducing additional atoms. However, there are still great challenges in realizing strainingof 2D materials with CMOS compatibility. Here, a method for large-scale ultrafast strain engineering of CVD-grown 2D materials is proposed. We introduce locally non-uniform strains through the cooperative deformation of materials and metal/metal oxide core/shell nanoparticles through cold laser shock. Raman and PL spectrareveal that the tensile strain of MoS2changes and the band gap decreases after laser shock. MD simulations are used to investigate the mechanism of the ultrafast straining of CVD-grown 2D materials. Field effect transistors of CVD MoS2were fabricated, and the performances before and after straining of the same devices are compared. By adjusting the strain level of MoS2, the field effect mobility can be increased from 1.9 cm2V-1s-1 to 44.1 cm2V-1s-1. This is the maximum value of MoS2FETs grown by CVDwith SiO2as dielectric. As an environment-friendly, large-scale and ultra-fast manufacturing method, laser shock provides a universal strategy for large-scale adjustment of 2D materials strain, which will help to promote the manufacturing of 2D nano electronic devices and optoelectronic devices.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2022-03-24
摘要: 非厄米的引入扩展了传统厄米量子系统中的概念并诱导出许多新奇的物理现象, 比如非厄米系统所独有的非厄米趋肤效应, 这使得对非厄米量子模型的模拟成为大家关注的热点. 相比于量子平台, 经典系统具有成本低廉、技术成熟、室温条件等优势, 而其中的经典电路系统则更加灵活, 原则上可以模拟任意维度、任意格点间跃迁、任意边界条件下的量子紧束缚模型, 已经成为模拟量子物态的有力平台.本文利用经典电路通过 SPICE 成功模拟了一个重要的非厄米量子模型 非互易 Aubry-Andr\'e 模型 的稳态性质, 此模型同时具有非互易的格点跃迁和准周期的格点在位势. 以此为例, 详细介绍了如何建立经典电路的拉普拉辛形式与量子紧束缚模型哈密顿矩阵在不同边界条件下的映射, 尤其是如何利用电流型负阻抗变换器构建模型的非互易性. 然后, 根据电路的格林函数, 通过 AC 电流驱动并测量电压响应的方式, 用 SPICE 模拟了周期边界条件下的复能谱和相应的能谱缠绕数, 以及开边界条件下的趋肤与局域模式的竞争.其中, 为了使电路的响应不发散, 本文还解析地给出辅助元件的设置原则.结果显示, SPICE 模拟与理论计算很好地吻合, 为进一步的实验实现提供了详细的指导. 由于本文电路设计与测量方案的普适性, 原则上可以直接应用于其他非厄米量子模型的电路模拟.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2021-12-18
摘要: True random number generator (TRNG) is an important component for modern information security technologies. Among the candidates, TRNG with spin-orbit torque (SOT)-induced probabilistic magnetization switching is competitive for its advantages in anti-radiation, unlimited endurance, robust stability, and broad temperature range. However, realization of a SOT-TRNG requires intensive understanding of the magnetic dynamic process under a spin-orbit current. Here, we performed micromagnetic simulation of the SOT-induced probabilistic magnetization switching by using Mumax 3. Without thermal noise, identical magnetic moment precessions were found between repeated simulation cycles, resulting in deterministic magnetization switching. When thermal noises were taken into account, stochastic precession trails and thereby probabilistic magnetization switching were finally obtained. Our results suggest the Mumax 3 to be a practical tool for simulating the probabilistic magnetization switching behavior of a SOT-TRNG, as well as highlighting the crucial role of thermal noise during the during the simulation.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2021-02-02
摘要: The past decade has witnessed a surge of interest in exploring emergent particles in condensed matter systems. Novel particles, emerged as excitations around exotic band degeneracy points, continue to be reported in real materials and artificially engineered systems, but so far, we do not have a complete picture on all possible types of particles that can be achieved. Here, via systematic symmetry analysis and modeling, we accomplish a complete list of all possible particles in time reversal-invariant systems. This includes both spinful particles such as electron quasiparticles in solids, and spinless particles such as phonons or even excitations in electric-circuit and mechanical networks. We establish detailed correspondence between the particle, the symmetry condition, the effective model, and the topological character. This obtained encyclopedia concludes the search for novel emergent particles and provides concrete guidance to achieve them in physical systems.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2020-12-12
摘要: We observed a counter-intuitive remarkable heating phenomenon generated by helium-4 superflows. This phenomenon establishes that superflows carry thermal energies and entropies, which is in contrast to the hypothesis of the two-fluid model. Quantum many-body theory of superfluids provides a natural understanding of the phenomenon.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2020-10-21
摘要: 本文提出过渡金属离子电子云的变化是非常规高温超导中电子的配对媒介,这类似于晶格振动是常规超导中电子的配对媒介。采用TDDFT方法的计算结果表明,过渡金属离子电子云振动的频率接近晶格振动频率,能够被自由电子激发。三种铜氧化物高温超导的计算结果表明,超导转变温度与电子云振动的频率高度相关。同时阐述了电子云变化与晶格振动的不同,电子云振动的特殊性能够解释非传统超导中电子的实空间配对、赝能隙、d波对称和同位素效应等。
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2019-07-02
摘要: P. W. Anderson raised an important question in 2007: Is There Glue in Cuprate Superconductors? The author believes that the change of the electron clouds of ions is the glue in cuprate superconductors. The change of the electron clouds of the ions in the parent structure of the layered high-temperature superconductors CaCuO2 has been studied by the first-principles calculations. The electron clouds of Cu2+ and O2- ions change obviously under electric fields. It is also found, for the first time, the characteristic frequencies of the change of the electron clouds are 250 meV, 360 meV, and 100 meV, respectively, for the modes observed. The frequencies are low and close to that of lattice vibrations, indicating the change of the electron cloud of ions can be the electron-pairing medium in cuprate superconductors.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2019-06-13
摘要: It is proposed that the electron-pairing medium of the iron-based superconductors may be the orbital fluctuation of the transition metal ions. But the characteristic frequency of the orbital fluctuation has not been given. For the first time, the author has calculated the real-time evolution of the electron clouds of transition metal ions in BaFe2As2 under excitations by the time-dependent density functional theory (TDDFT). There are different modes of fluctuations. The characteristic frequencies are 150 meV, 160 meV, 250 meV, and 200 meV, respectively, for the modes the author observed. The results are unexpected, because the general view is that the change of the electron density is very quick, and the frequency is much higher than the lattice vibration. The frequencies the author obtained are close to that of the lattice vibration in conventional superconductors at normal and high pressures, indicating the orbital (or electron cloud) fluctuation can by the electron pairing medium. Based on the calculation results, the author proposed a new electron pairing mechanism.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2019-04-24
摘要: The electron-pairing mechanism in unconventional high temperature superconductors (HTS) has not been resolved. The author proposed that the electron-pairing medium of unconventional HTS is the change of the electron clouds of transition metal ions, which is analogous to the lattice vibration in conventional superconductors. Real-time evolution of the electron clouds of transition metal ions under excitations in La2Fe2As2O2, FeSe sheet, Fe2KSe2, CaCuO2, and HgBa2Ca2Cu3O8 was calculated by the time-dependent density functional theory (TDDFT). The characteristic frequency is about 90-250 meV, which is equivalent to the lattice vibration frequencies, showing that the change of the electron clouds of the transition metal ions can be the electron-pairing medium in unconventional HTS.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2018-04-24
摘要: 采用基于密度泛函理论的第一性原理计算方法研究了铁基超导体和铜基超导体中的电场效应。研究对象包括铁基超导体(KFe2Se2,LaFeAsO,NdFeAsO,BaFe2As2)和铜基超导体(YBa2Cu3O7,HgBa2Ca2Cu3O8,Tl2Ba2CaCu2O8,Bi2Sr2Ca2Cu3O10)。为了描述3d电子或4f电子的强关联效应,采用GGA+U方法。并采用HSE方法进一步验证了结果。给出了态密度(DOS)。给出了电场作用下体系的电荷密度的变化。发现铁基超导体中的铁离子的电子云,NdFeAsO中钕离子的电子云,铜基超导体铜离子的电子云变化明显。变化的模式更像刚体旋转而不是弹性变形。作者认为,过渡金属离子电子云的转动可能是超导电子配对的一种新媒介。在此基础上提出了一种新的超导电子配对机制。
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2017-11-27
摘要: Cubic helimagnet FeGe has emerged as a class of skyrmion materials near room temperature that may impact future information technology. Experimentally identifying the detailed properties of skyrmion materials enables their practical application acceleratedly. Here we study the magnetic entropy change (MEC) of single crystalline FeGe in its precursor region and clarify its close relation to the critical exponents of a second-order phase transition in this area. The maximum MEC is found to be 2.86 J/kg.K for 7.0 T magnetic field change smaller than that of common magnetocaloric materials indicating the multiplicity and complexity of the magnetic structure phases in the precursor region. This result also implies that the competition among the multimagnetic phases can partly counteract the magnetic field driven force and establishes a stable balance. Based on the obtained MEC and the critical exponents, the exact Curie temperature of single crystalline FeGe under zero magnetic field is confirmed to be 279.1 K, higher than previously reported 278.2 K. This finding pave the way for reconstruction of FeGe phase diagram in the precursor region.
分类: 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间: 2017-11-27
摘要: The magnetic entropy change [ΔSM(T;H)] around the phase transition temperature TC is investigated by the scaling method for Fe0:5Co0:5Si, which exhibits a skyrmion phase below TC. The parameters of ΔSM(T;H) exhibit field dependent behaviors. The ΔSM(T;H) curves under high field can be well scaled into a single universal curve independent of external field and temperature. However, ΔSM(T;H) curves under low field become divergent just below TC, which indicates a characteristic of first-order transition. The scaling investigation of ΔSM(T;H) curves indicates that the phase transition in Fe0:5Co0:5Si is of a weak first-order type in low field region, while it is driven into a second-order one under high field. This weak first-order phase transition in low field region resembles that in typical skyrmion system MnSi which is caused by the critical fluctuation. The result suggests that critical fluctuation plays an important role in the phase transition and formation of skyrmion state.