Subjects: Electronics and Communication Technology >> Electron Technology Subjects: Engineering and technical science >> Technology of Instrument and Meter Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2024-05-06
Abstract: In this work, we design and fabricate the transimpedance Amplifier (TIA) following the design mentioned in Ref. 1 . 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 (Post-Amp) is made of an operational amplifier. Cascade Pre-Amp and Post-Amp to form the inverting-amplifier. 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. As an example, the realization of TIA in this work verifies the design method and analytical calculations for the low-noise large-bandwidth high-gain TIA proposed in Ref. 1,2 . And, the TIA in this work is perfect for the cryogenic STM working at liquid nitrogen temperature.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2024-04-17
Abstract: 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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2024-03-26
Abstract: 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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2024-01-20
Abstract: 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 loss rate of the order of $10^{-5}$, showing 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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2022-12-09
Abstract:
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2022-10-21
Abstract: 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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2022-09-06
Abstract: Using the micromagnetics simulations, it is shown that the spin transfer torques (STT) of electrons are only exerted on the magnetic moments at two ends of single nanowire where they are misaligned with the direction of polarized current density (J ). By increasing the polarization rate (P) of current, microwave magnetic losses at 18 GHz can be obviously suppressed in this very simplified model. It is also found that the natural resonance frequency can no be changed by the STT effect. Negative imaginary parts of permeability are also shown feasible under the STT effect. On the other hand, the results also show that the microwave magnetic losses at 18 GHz can be enhanced by increasing the β value in the non-adiabatic term. It can be well understood from the change of effective damping constant (ɑe) due to the different contributing torques of STT effect. The adiabatic torque of STT will decrease ɑe value and therefore suppress the microwave magnetic losses. The non-adiabatic torque of STT will increase ɑe value and therefore enhance the microwave magnetic losses. These results show an active and innovative way to control the microwave magnetic losses.
Peer Review Status:Awaiting Review
Subjects: Computer Science >> Other Disciplines of Computer Science Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2022-08-15
Abstract: With the development of high-performance computing architectures, many software and hardware have a multi-layer parallel structure. A large amount of allocation schemes can be involved when users allocate multi-layered system resources to many computational tasks distributed in different vertical tiers and horizontal groupings. It is becoming increasingly difficult for users to determine the optimal parallel parameters and hardware resource usage. We investigate an optimization method which is helpful for users to automate the determination of the optimal application parallel parameters and hardware usage for high-efficient and/or large-scale computation. In addition, we propose a solution that deeply integrates the optimization method with the job scheduling system, which has produced excellent practical results.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2022-04-30
Abstract:
Strain engineering of 2D materials is capable of tuning the electrical and optical properties of the materials without introducing additional atoms. However, there are still great challenges in realizing straining of 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 spectra reveal that the tensile strain of MoS2 changes 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 MoS2 were 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 MoS2 FETs grown by CVD with SiO2 as 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.
Peer Review Status:Awaiting Review
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc. Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties Subjects: Physics >> Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology submitted time 2022-03-24
Abstract:
The introduction of non-Hermiticity into traditional Hermitian quantum systems generalizes their basic notions and brings about many novel phenomena, e.g., the non-Hermitian skin effect that is exclusive to non-Hermitian systems, attracting enormous attention from almost all branches of physics. Contrary to the quantum platforms, classical systems have the advantages of low cost and mature techniques under room temperature. Among them, the classical electrical circuits are more flexible on simulating quantum tight-binding models in principle with any range of hopping under any boundary conditions in any dimension, and have become a powerful platform for the simulation of quantum matters. In this paper, by constructing an electrical circuit, we simulate by SPICE the static properties of a prototypical non-Hermitian model --- the nonreciprocal Aubry-Andr\'e (AA) model that has the nonreciprocal hopping and on-site quasiperiodic potentials.
The paper is organized as follows: Following the introduction, in Sec. II we review in detail the Laplacian formalism of electrical circuits and the mapping to the quantum tight-binding model. Then, in Sec. III, an electrical circuit is proposed with resistors, capacitors, inductors, and the negative impedance converters with current inversion (INICs), establishing a mapping between the circuit's Laplacian and the non-reciprocal AA model's Hamiltonian under periodic boundary conditions (PBCs) or open boundary conditions (OBCs). Especially, the nonreciprocity, the key of this model, is realized by INICs. In Sec IV, based on the mapping, for the proposed circuit under PBCs, we reconstruct the circuit's Laplacian via SPICE by measuring voltage responses of an AC current input at each node. The complex spectrum and its winding number $\nu$ can be calculated by the measured Laplacian, which are consistent with the theoretical prediction, showing $\nu=\pm 1$ for non-Hermitian topological regimes with complex eigenenergies and extended eigenstates, and $\nu=0$ for topologically trivial regimes with real eigenenergies and localized eigenstates. In Sec V, for the circuit under OBCs, a similar method is used for measuring the node distribution of the voltage response, which simulates the competition of non-Hermitian skin effects and the Anderson localization, depending on the strength of quasiperiodic potentials; the phase transition points also appear in the inverse participation ratios of the voltage responses.
During the design process, the parameters of auxiliary resistors and capacitors are evaluated for obtaining stable responses, because the complex eigenfrequecies of the circuits are inevitable under PBCs. Our detailed scheme can directly instruct further potential experiments, and the designing method of the electrical circuit is universal and can in principle be applied to the simulation for other quantum tight-binding models.
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Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2021-12-18
Abstract: 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. " " "
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties Subjects: Physics >> Interdisciplinary Physics and Related Areas of Science and Technology submitted time 2021-02-02
Abstract: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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc. submitted time 2020-12-12
Abstract: "
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2020-10-21
Abstract: "
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2019-07-02
Abstract: " 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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2019-06-13
Abstract: " 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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2019-04-24
Abstract: "
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2018-04-24
Abstract: Electric field effects in iron- and copper-based superconductors were studied by using the first-principles calculations based on the density functional theory (DFT). The research objects include iron-based superconductors (KFe2Se2, LaFeAsO, NdFeAsO, and BaFe2As2) and copper-based superconductors (YBa2Cu3O7, HgBa2Ca2Cu3O8, Tl2Ba2CaCu2O8, and Bi2Sr2Ca2Cu3O10). To describe the strong correlation effect of 3d-electrons or 4f-electrons, the GGA+U method was used. Some results were further verified by the HSE method. The densities of states (DOS) were given. The change of the charge densities under electric fields is presented to demonstrate the electric field effect. It is found that the electron clouds of Fe ions in iron-based superconductors, Nd ions in Nd2Fe2As2O2, and Cu ions in copper-based superconductors change obviously. The pattern of the change is more like a rigid-body rotation than an elastic deformation. The author proposed that the rotation of the electron clouds of transition metal ions may be a new medium of superconducting electron pairing. The author’s views about some issues and suggestions on follow-up studies are also presented.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2017-11-27
Abstract: 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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Electronic Structure, Electrical, Magnetic, and Optical Properties submitted time 2017-11-27
Abstract: 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.
Peer Review Status:Awaiting Review