Ground State Research Articles

High acoustic velocity x-cut lithium niobate sub-terahertz electromechanics

Micromechanical resonators operating above 100 GHz are favorable candidates for quantum physics studies due to their stronger ability to withstand thermal fluctuations, allowing them to remain in the quantum ground state even at kelvin temperatures. Furthermore, electromechanical resonators at sub-terahertz frequencies enable high-speed data transfer in modern communication technologies, making them attractive for communication industries. Recently, sub-terahertz electromechanics has been demonstrated on z-cut thin-film lithium niobate. Yet, the x-cut thin-film lithium niobate is more advantageous for scaling above 100 GHz due to its faster acoustic velocity. Here, we report sub-terahertz electromechanics on x-cut thin-film lithium niobate utilizing the thickness-longitudinal mode. In addition, we study the orientation dependence of these mechanical resonators due to the anisotropy of lithium niobate. We find that devices with a cross section close to the xy plane can be more efficiently excited, in contrast to those near the xz plane. This difference stems from the orientation-dependent nature of the e12 piezoelectric coupling element of the x-cut lithium niobate film. This investigation could assist in optimizing resonator designs by choosing the crystallographic direction that offers the best performance for specific functionalities.

Magnetic properties of ferro-antiferromagnetic spin triangle chain

Frustrated spin- 12 model consisting of a linear chain of triangles with ferro (F)- and antiferromagnetic interactions connected by ferromagnetic interactions (triangles chain) is studied. The ground state phase diagram depending on the interaction ratios consists of ferromagnetic, two ferrimagnetic and singlet phases. The magnetic properties in these phases are analyzed both analytically and numerically. We show that in some regions of the singlet phase the magnetization curves have magnetization plateau and magnetization jumps. We study the thermodynamics and its relation to the specific structure of the excitation spectrum of the triangle chain.

Experimental Study on High-Speed Aviation Gear Scuffing Based on Tooth Profile and Surface Treatment Improvements

Scuffing failure in high-speed aviation gears is a critical issue that hinders the improvement of operating performance and reliability in modern aviation equipment. The unclear failure mechanism limits the effective design of anti-scuffing measures. In this study, a scuffing test method was designed for high-speed aviation gears to investigate the effects of tooth profiles and surface treatment on the gear scuffing performance. The results indicate that both the pressure angle and surface treatment significantly affect gear scuffing behavior. Under different geometric treatment states, the range of the Ryder load stages at which gear scuffing initiated was between 5 and 13. The 25° pressure angle gear with barrel finishing treatment exhibited the optimal anti-scuffing performance. Compared to the ground state, barrel finishing increases gear scuffing loading capacity by 30% to 33%. Tooth profile optimization based on pressure angle changes improves gear loading capacity by 56.9%. This work provides an exploration of the anti-scuffing design of high-speed gears.

Visible Light Induced Exciton Dynamics and trans-to-cis Isomerization in Azobenzene Aggregates: Insights from Surface Hopping/Semiempirical Configuration Interaction Molecular Dynamics Simulations.

Assemblies of photochromic molecules feature exciton states, which govern photochemical and photophysical processes in multichromophoric systems. Understanding the photoinduced dynamics of the assemblies requires nonadiabatic treatment involving multiple exciton states and numerous nuclear degrees of freedom, thus posing a challenge for simulations. In this work, we address this challenge for aggregates of azobenzene, a prototypical molecular switch, performing on-the-fly surface hopping calculations combined with semiempirical configuration interaction electronic structure and augmented with transition density matrix analysis to characterize exciton evolution. Specifically, we consider excitation of azobenzene tetramers in the nπ* absorption band located in the visible (blue) part of the electromagnetic spectrum, thus extending our recent work on dynamics after ππ* excitation corresponding to the ultraviolet region [Titov, J. Phys. Chem. C2023, 127, 13678-13688]. We find that the nπ* excitons, which are initially strongly localized by ground-state conformational disorder, undergo further (very strong) localization during short-time photodynamics. This excited-state localization process is extremely ultrafast, occurring within the first 10 fs of photodynamics. We observe virtually no exciton transfer of the localized excitons in the nπ* manifold. However, the transfer may occur via secondary pathways involving ππ* states or the ground state. Moreover, we find that the nπ* quantum yields of the trans-to-cis isomerization are reduced in the aggregated state.

AbInitio Calculation of the Alpha-Particle Monopole Transition Form Factor.

We present a parameter-free abinitio calculation of the α-particle monopole transition form factor in the framework of nuclear lattice effective field theory. We use a minimal nuclear interaction that was previously used to reproduce the ground state properties of light nuclei, medium-mass nuclei, and neutron matter simultaneously with no more than a few percent error in the energies and charge radii. The results for the monopole transition form factor are in good agreement with recent precision data from Mainz.

Sub-Doppler laser cooling and magnetic trapping of natural-abundance fermionic potassium

We demonstrate the largest number of 40K atoms that has ever been cooled to deeply sub-Doppler temperatures in a single-chamber apparatus without using an enriched source of potassium. With gray molasses cooling on the D 1-line following a standard D 2-line magneto-optical trap, we obtain 3×105 atoms at 10(2) µK. We reach densities high enough to measure the temperature via absorption imaging using the time-of-flight method. We magnetically trap a mixture of mF=−3/2,−5/2 and −7/2 Zeeman states of the F=7/2 hyperfine ground state confining 5×104 atoms with a lifetime of 0.6 s or ∼103 atoms with a lifetime of 2.8 s—depending on whether the temperature of the potassium dispensers was chosen to maximize the atom number or the lifetime. The background pressure-limited lifetime of 0.6 s is a reasonable starting point for proof-of-principle experiments with atoms and/or molecules in optical tweezers as well as for sympathetic cooling with another species if transport to a secondary chamber is implemented. Our results show that unenriched potassium can be used to optimize experimental setups containing 40K in the initial stages of their construction, which can effectively extend the lifetime of enriched sources. Moreover, the demonstration of sub-Doppler cooling and magnetic trapping of a relatively small number of potassium atoms might influence experiments with laser-cooled radioactive isotopes of potassium.

Bistability between π-diradical open-shell and closed-shell states in indeno[1,2-a]fluorene.

Indenofluorenes are non-benzenoid conjugated hydrocarbons that have received great interest owing to their unusual electronic structure and potential applications in nonlinear optics and photovoltaics. Here we report the generation of unsubstituted indeno[1,2-a]fluorene on various surfaces by the cleavage of two C-H bonds in 7,12-dihydroindeno[1,2-a]fluorene through voltage pulses applied by the tip of a combined scanning tunnelling microscope and atomic force microscope. On bilayer NaCl on Au(111), indeno[1,2-a]fluorene is in the neutral charge state, but it exhibits charge bistability between neutral and anionic states on the lower-workfunction surfaces of bilayer NaCl on Ag(111) and Cu(111). In the neutral state, indeno[1,2-a]fluorene exhibits one of two ground states: an open-shell π-diradical state, predicted to be a triplet by density functional and multireference many-body perturbation theory calculations, or a closed-shell state with a para-quinodimethane moiety in the as-indacene core. We observe switching between open- and closed-shell states of a single molecule by changing its adsorption site on NaCl.

Spectroscopic properties and laser cooling feasibility with the X1∏21/2↔X2∏23/2 transition for the PbX (X = F, Cl, Br, and I) molecules

The highly diagonal Frank–Condon factors (FCFs) are necessary for the laser cooling scheme, which means that only the molecules with the appropriate ground and excited electronic states can become candidates. Here, the laser cooling feasibility of the PbX (X = F, Cl, Br, and I) molecules is explored through four-component relativistic calculations. The potential energy curves and transition dipole moments of five Ω states are calculated and used to solve the Schrödinger equation of nuclear motion to obtain the rovibrational energy levels, spectroscopic parameters, the Einstein coefficients, and FCFs. Using the X1 2Π1/2 ↔ X2 2Π3/2 transition with highly diagonal FCFs, we construct optical schemes that can provide 104 ∼ 105 scattering phonons with four pumping lasers for PbX. The Doppler/recoil temperatures of PbX are 419.05 / 57.55, 9.63 / 61.20, 4.95 / 49.98, and 0.71 / 40.17 nK, respectively. Since the 10−4 s of the long spontaneous emission lifetime, the temperatures below microkelvin orders of magnitude can be achieved only if the adequate pre-cooling temperature is satisfied.

Bright solitons in a spin-orbit-coupled dipolar Bose-Einstein condensate trapped within a double-lattice.

By effectively controlling the dipole-dipole interaction, we investigate the characteristics of the ground state of bright solitons in a spin-orbit coupled dipolar Bose-Einstein condensate. The dipolar atoms are trapped within a double-lattice which consists of a linear and a nonlinear lattice. We derive the motion equations of the different spin components, taking the controlling mechanisms of the dipole-dipole interaction into account. An analytical expression of dipole-dipole interaction is derived. By adjusting the dipole polarization angle, the dipole interaction can be adjusted from attraction to repulsion. On this basis, we study the generation and manipulation of the bright solitons using both the analytical variational method and numerical imaginary time evolution. The stability of the bright solitons is also analyzed and we map out the stability phase diagram. By adjusting the long-range dipole-dipole interaction, one can achieve manipulation of bright solitons in all aspects, including the existence, width, nodes, and stability. Considering the complexity of our system, our results will have enormous potential applications in quantum simulation of complex systems.

A comprehensive investigation of ethyl 2-(3-methoxybenzyl) acrylate substituted pyrazolone analogue: Synthesis, computational and biological studies

In this study, we successfully synthesized ethyl 2-(3-methoxybenzyl) acrylate-substituted pyrazolones derivative (EMH) through the reaction of Baylis-Hillman acetate with pyrazolones. We conducted comprehensive screenings to evaluate its invitro antifungal, antibacterial, and antioxidant properties. The molecule demonstrated notable in vitro antifungal and antibacterial activities attributed to the presence of anisole, enhancing absorption rates through increased lipid solubility and improving pharmacological effects. Structure-activity relationship (SAR) studies supported these findings. Additionally, insilico studies delved into the molecular interactions of the synthesized molecule with DNA Gyrase, Lanosterol 14 alpha demethylase, and KEAP1-NRF2 proteins, revealing strong binding interactions at specific sites. Furthermore, we employed ab-initio techniques to theoretically estimate the photophysical properties of the compounds. Ground state optimization, dipole moment, and HOMO-LUMO energy levels were calculated using the DFT-B3LYP-6-31G(d) basis set. The theoretical HOMO-LUMO values indicated high electronegativity and electrophilicity index. NBO analysis confirmed the presence of intermolecular ON...H hydrogen bonds resulting from the interaction of the lone pair of oxygen with the anti-bonding orbital. Overall, our results suggest that anisole-substituted pyrazolones derivatives exhibit promising applications in both photophysical and biological domains.

Dependence of protective effect of Ti1–xAlxN coatings in 3 wt.% NaCl solution on dissolution mechanism of their phases c‐Ti0.5Al0.5N, c‐AlN, and c‐TiN

AbstractThe dissolution mechanism of phases c‐Ti0.5Al0.5N, c‐aluminium nitride (AlN), c‐TiN, and Al2Ti, and elements of the Ti1–xAlxN coatings (for x < 0.6) in 3 wt.% NaCl solution is described based on the results of X‐ray diffraction analysis, energy‐dispersive X‐ray spectroscopy, and scanning electron microscope and previous electrochemical tests. Researchers studied the protective effectiveness of Ti1–xAlxN coatings in 3 wt.% NaCl solution by analyzing the factors: composition, thickness, porosity, total energy of ground state, stresses, structure, and texture. It was first established that the additional c‐TiN phase with Rpmax and Ecormax, and secondary phase Ti0.70–0.82N formed after Al's dissolution in the main phase c‐Ti0.5Al0.5N increases the N content and prevents the Ti dissolution in the Ti1–xAlxN coatings. The phase c‐AlN with icormin reduces the dissolution rate of Al in the c‐Ti0.5Al0.5N phase. The stoichiometric c‐Ti0.5Al0.5N is the most thermodynamically stable phase. The described phase transformations in Ti1–xAlxN coatings during phases dissolution in 3 wt.% NaCl can predict the coating protective effect. A multilayer coating with layers of c‐AlN, c‐TiN, and c‐Ti0.5Al0.5N is recommended for industrial use.

Cationic disorder: Governing the spin-insulatronic properties of nanocrystalline ZnFe2O4 thin films

Controlling cation order/disorder in spinel offers a highly effective means of tailoring material properties by modifying inter- and intra-sub-lattice ionic interactions. In this study, we conducted high-temperature magnetization measurements (300–1000 K) to determine average Curie temperatures (TC) for nanocrystalline ZnFe2O4 thin films. Thermodynamical stability of these films under extreme conditions was investigated by assessing lattice structures, oxygen vacancies, magnetization, and electric resistivity for spin-insulatronic applications. Reversible cation inversion via heat treatments (in-situ and ex-situ) yields tunable ferrimagnetic (FiM) order in ZnFe2O4, with TC ranging from 425 to 710 K. First-principles calculations highlight effective cation inversion mitigating magnetic frustration, promoting collinear FiM ordering, and elevating TC. Oxygen vacancies further reinforce ferrimagnetism, slightly reducing resistivity through the formation of Fe-3d gap states near the Fermi level. A proposed magnetic nanophase diagram elucidates dominant competing magnetic ground states (cluster spin-glassy state, FiM, and antiferromagnetic) with increasing growth temperature, fostering innovative homo-architectures from multiple ZnFe2O4 thin films with diverse functionalities.

Large N master field optimization: the quantum mechanics of two Yang-Mills coupled matrices

We study the large N dynamics of two massless Yang-Mills coupled matrix quantum mechanics, by minimization of a loop truncated Jevicki-Sakita effective collective field Hamiltonian. The loop space constraints are handled by the use of master variables. The method is successfully applied directly in the massless limit for a range of values of the Yang-Mills coupling constant, and the scaling behaviour of different physical quantities derived from their dimensions are obtained with a high level of precision. We consider both planar properties of the theory, such as the large N ground state energy and multi-matrix correlator expectation values, and also the spectrum of the theory. For the spectrum, we establish that the U(N) traced fundamental constituents remain massless and decoupled from other states, and that bound states develop well defined mass gaps, with the mass of the two degenerate lowest lying bound states being determined with a particularly high degree of accuracy. In order to confirm, numerically, the physical interpretation of the spectrum properties of the U(N) traced constituents, we add masses to the system and show that, indeed, the U(N) traced fundamental constituents retain their “bare masses”. For this system, we draw comparisons with planar results available in the literature.

Circumventing data imbalance in magnetic ground state data for magnetic moment predictions

Magnetic materials play a crucial role in the transition to more sustainable forms of energy and electric vehicles. There is an anticipated shortage in magnetic materials in the future, and as a result there is an urgent need to discover and design new magnetic materials. Computational magnetic material design using density functional theory is daunting because of the challenge in identifying magnetic ground states from a combinatorially large set of possibilities. Machine learning offers a path forward by enabling efficient surrogate models that can more readily enumerate these states, but there is a dearth of training data available, and what is available tends to be imbalanced with too much non-magnetic data. In this work we show that the discrete and previously tackled data imbalance that exists at the level of the magnetic ordering leads to an imbalanced continuous distribution with many zeros when the data is unraveled at the atomic magnetic moment level, which subsequently leads to models with low accuracy for magnetic properties. We mitigate this by using a two-part model framework. Our scheme is able to classify atoms into magnetic and non-magnetic with an F1 score and Matthew’s correlation coefficient (MCC) of ~91% and then to provide an implicit embedding representation that maps directly onto the magnitude of the magnetic moment with a mean absolute error of 0.1 μB . Beyond screening for new magnetic materials, we demonstrate an additional practical use case of our scheme: the provision of good initial guesses for magnetic moments in first-principles electronic relaxations. Such initialization is shown to lead to faster convergence to configurations that lie closer to the ground state.

Emergent Superconductivity and Competing Charge Orders in Hole-Doped Square-Lattice t-J Model.

The square-lattice Hubbard and closely related t-J models are considered as basic paradigms for understanding strong correlation effects and unconventional superconductivity (SC). Recent large-scale density matrix renormalization group simulations on the extended t-J model have identified d-wave SC on the electron-doped side (with the next-nearest-neighbor hopping t_{2}>0) but a dominant charge density wave (CDW) order on the hole-doped side (t_{2}<0), which is inconsistent with the SC of hole-doped cuprate compounds. We re-examine the ground-state phase diagram of the extended t-J model by employing the state-of-the-art density matrix renormalization group calculations with much enhanced bond dimensions, allowing more accurate determination of the ground state. On six-leg cylinders, while different CDW phases are identified on the hole-doped side for the doping range δ=1/16-1/8, a SC phase emerges at a lower doping regime, with algebraically decaying pairing correlations and d-wave symmetry. On the wider eight-leg systems, the d-wave SC also emerges on the hole-doped side at the optimal 1/8 doping, demonstrating the winning of SC over CDW by increasing the system width. Our results not only suggest a new path to SC in general t-J model through weakening the competing charge orders, but also provide a unified understanding on the SC of both hole- and electron-doped cuprate superconductors.

Photo-Controlled Reversible Uptake and Release of a Modified Sulfamethoxazole Antibiotic Drug from a Pillar[5]arene Cross-Linked Gelatin Hydrogel.

Pillararene cross-linked gelatin hydrogels were designed and synthesized to control the uptake and release of antibiotics using light. A suite of characterization techniques ranging from spectroscopy (FT-IR, 1H and 13C NMR, and MAS NMR), X-ray crystallographic analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) was employed to investigate the physicochemical properties of hydrogels. The azobenzene-modified sulfamethoxazole (Azo-SMX) antibiotic was noncovalently incorporated into the hydrogel via supramolecular host-guest interactions to afford the A-hydrogel. While in its ground state, the Azo-SMX guest has a trans configuration structure and forms a thermodynamically stable inclusion complex with the pillar[5]arene motif in the hydrogel matrix. When the A-hydrogel was exposed to 365 nm UV light, Azo-SMX underwent a photoisomerization reaction. This changed the structure of Azo-SMX from trans to cis, and the material was released into the environment. The Azo-SMX released from the hydrogel was effective against both Gram-positive and Gram-negative bacteria. Importantly, the A-hydrogel exhibited a striking difference in antibacterial activity when applied to bacterial colonies in the presence and absence of UV light, highlighting the switchable antibacterial activity of A-hydrogel aided by light. In addition, all hydrogels containing pillar[5]arenes have demonstrated biocompatibility and effectiveness as scaffolds for biological and medical purposes.

Normalized ground states to the p-Laplacian equation with general nonlinearities

In this paper, we consider the existence of ground state solutions to the following p-Laplacian equation{−Δpu+λ|u|p−2u=f(u)inRN,∫RN|u|pdx=a>0, where 1<p<N and λ∈R. Under general assumptions on the nonlinearity f, we treat two cases. Firstly, in a Lp -subcritical framework, we show the existence of ground state solutions with negative energy and zero, which is a global minimizer. Secondly, in the at least Lp-critical growth, we establish the existence of a mountain pass solution at positive energy level by exploiting a natural constraint related to the Pohozaev identity.

Signatures of a surface spin–orbital chiral metal

The relation between crystal symmetries, electron correlations and electronic structure steers the formation of a large array of unconventional phases of matter, including magneto-electric loop currents and chiral magnetism1–6. The detection of such hidden orders is an important goal in condensed-matter physics. However, until now, non-standard forms of magnetism with chiral electronic ordering have been difficult to detect experimentally7. Here we develop a theory for symmetry-broken chiral ground states and propose a methodology based on circularly polarized, spin-selective, angular-resolved photoelectron spectroscopy to study them. We use the archetypal quantum material Sr2RuO4 and reveal spectroscopic signatures that, despite being subtle, can be reconciled with the formation of spin–orbital chiral currents at the surface of the material8–10. As we shed light on these chiral regimes, our findings pave the way for a deeper understanding of ordering phenomena and unconventional magnetism.

Spin–spin interaction in a highly stable neutral diradical: σ-boned dimer of trioxotriangulene

Abstract A σ-bonded dimer of 4,8,10-trioxotriangulene (TOT) was newly synthesized and its electronic spin structure was characterized. The neutral diradical had a singlet ground state due to the strong antiferromagnetic interaction through the σ-bond. The strong intramolecular interaction within the σ-dimer caused a near-infrared photoabsorption of around 700–1,000 nm, which is close to that of the π-stacked dimer of TOT monoradical.

Electronic structure of ground and low-lying excited states of BaLi+ molecular ion: spin-orbit effect, radiative lifetimes and Franck-Condon factor

The study of BaLi+ and its reactivity plays a crucial role in advancing our understanding of chemical bonding or reaction mechanisms. The aim of this work is to represent a complete and extended theoretical study of BaLi+ molecular ion including ground and highly excited electronic states of 1,3Σ, 1,3Π and 1,3Δ symmetries, dissociated to the first seven dissociation limits. The corresponding potential energy curves (PECs), permanent and transition dipole moments have been investigated. These calculations were performed using the multireference configuration interaction (MRCI) method in combination with optimized basis sets and non-empirical pseudopotentials (ECP) for both Ba and Li atoms. Afterwards, the spin–orbit (SO) operator is incorporated in valence MRCI calculation using optimized relativistic spin–orbit pseudopotentials and 16 Ω states are generated and splitted into Λ-S states. The SO effect gives rise to a more complicated structure of electronic states presented in PEC and permanent and transition dipole moments. Nonadiabatic coupling matrix elements between the five lowest 1Σ+ states are also presented for the nonrelativistic results. Based on the vibrational radiative lifetime and Franck–Condon calculation, the possibilities of laser cooling of this system have been also discussed.