Minimum Energy and Total Dipole Moment

Several magnetic materials consisting of dipoles owe their properties to the specific nature of the dipole–dipole interaction. In the present work, systems of particles possessing a dipole moment arranged on various types of 2D and 3D structures, completely arbitrary and, in some 2D instances, periodic (albeit finite), are studied. Noteworthy, the work is in the regime of strong dipole moments where a classical treatment is possible. The ultimate goal is to quantitatively address the unknown relation existing between the minimum possible energy of a system of dipoles and the concomitant total dipole moment. To such an end, classical numerical methods are used to the previous minimum energy–total dipole moment tandem for various magnetic configurations at zero temperature. An analytic bound for the minimal energy valid for any dimension is also obtained. With this exploration, new light is shed on the connection between the two former physical quantities, establishing an analytic inequality for $N=3$ particles, and describing other instances of physical interest.     

Large Magnetic Anisotropy Energy and Robust Half-Metallic Ferromagnetism in 2D MnXSe4 (X = As,Sb)

In recent years, intrinsic 2D magnetism has aroused great interest because of its potential application in spintronic devices. However, low Curie temperature (T_c) and magnetic anisotropy energy (MAE) limit its application prospects. Here, using first-principles calculations based on density-functional theory, a series of stable MnXSe₄ (X=As, Sb) single-layer is predicted. The MAE of single-layer MnAsSe₄ and MnSbSe₄ is 648.76 and 808.95 $\mu$eV per Mn atom, respectively. Monte Carlo simulations suggest the T_c of single-layer MnAsSe₄ and MnSbSe₄ is 174 and 250 K, respectively. The energy band calculation with hybrid Heyd–Scuseria–Ernzerhof (HSE06) function indicates the MnXSe₄ (X = As, Sb) is ferromagnetic half-metallic. Also, it has 100% spin-polarization ratio at the Fermi level. For MnAsSe₄ and MnSbSe₄, the spin-gaps are 1.59 and 1.48 eV, respectively. These excellent magnetic properties render MnXSe₄ (X = As, Sb) as promising candidate materials for 2D spintronic applications.     

Possible Link between the Distribution of Atomic Spectral Lines and the Radiation–Matter-Equilibrium in the Early Universe

The uncanny resemblance of the global distribution of all experimentally known atomic spectral lines to the Planckian spectral distribution associated with black body radiation at a temperature of $T\approx 9000\mathrm{K}$ is reported. This value coincides with the critical temperature of equilibrium between the respective densities of radiation and matter in the early universe.     

Efficient Ultraviolet Nanosources Based on Third-Harmonic Generation in Dielectric–Metal Composite Nanodisks

Dielectric materials with high indices have recently attracted much attention in the community of nanophotonics. Severe optical losses in visible–ultraviolet (UV) region, however, limit their applications. This article proposes dielectric–metal nanocomposites as alternative high-index materials for Mie-resonance-based applications. Such composite materials have high indices in the range of wavelength longer than plasmon resonance of inclusion metal nanoparticles, while they have much lower losses in the range from blue-violet down to near-UV compared with commonly used high-index materials such as silicon, enabling near-UV generation with high efficiency based on third-harmonic generation (THG). The numerical results show that ZnO nanodisk containing silver nanoparticles can generate near-UV radiation at 351.3 nm via THG with an efficiency about 20 times higher compared with silicon nanodisk under same pumping condition. Significantly high THG efficiency of 0.015% has been predicted with such a composite nanodisk supported by aluminum substrate under pumping with a peak intensity of 20 GW cm⁻², a spot size of 0.8 $\mu \mathrm{m}$, a duration of 50 fs at 1054 nm, respectively.     

Phantom Cosmological Model with Observational Constraints in f(Q)$f(Q)$ Gravity

In this paper, the cosmological model of the Universe has been presented in $f(Q)$ gravity and the parameters are constrained from the cosmological data sets. At the beginning, a well motivated form of $f(Q)=\alpha +\beta Q^n$ has been employed, where α, β, and n are model parameters. The Hubble parameter is obtained in redshift with some algebraic manipulation from the considered form of $f(Q)$. Then it is parameterized with the recent $\text{Hubble}$ data and $\text{Pantheon}+\text{SHOES}$ data using Markov chain Monte Carlo analysis. The obtained model parameter values are validated with the baryon acoustic oscillation data set. A parametrization of the cosmographic parameters shows the early deceleration and late time acceleration with the transition at $z_{\mathrm{t}}\approx 0.75$. The $Om(z)$ diagnostics gives positive slope which shows that the model is in the phantom phase. Also the current age of the Universe has been obtained as, $t_0=13.85\text{Gyrs}$. Based on the present analysis, it indicates that the $f(Q)$ gravity may provide an alternative to dark energy for addressing the current cosmic acceleration.     

Phase Diagrams of Periodically Driven Spin–Orbit Coupled 87Rb and 23Na Bose–Einstein Condensates

The phase boundaries of periodically driven spin–orbit coupled BECs with effective two‐body interactions are analytically calculated by using variational method. The phase diagrams of periodically driven ${}^{87}\mathrm{Rb}$ and ${}^{23}\mathrm{Na}$ systems present distinguished features from undriven systems, respectively. For the ${}^{87}\mathrm{Rb}$ BECs, the critical density $n_c$ (density at quantum tricritical point) will be dramatically reduced in some parameter regions, and the prospect of observing this intriguing quantum tricritical point is greatly enlarged. Moreover, a series of quantum tricritical points emerge quasi‐periodically when increasing the Raman coupling strength with fixed ${}^{87}\mathrm{Rb}$ density. In the ${}^{23}\mathrm{Na}$ BECs, two hyperfine states of ${}^{23}\mathrm{Na}$ atoms can be miscible within the suitable regions of driving parameter space. As a result, ${}^{23}\mathrm{Na}$ systems will stay in the stripe phase with small Raman frequency at typical density, which expands the region of stripe phase in the phase diagram. In addition, an absence of quantum tricritical point in such ${}^{23}\mathrm{Na}$ system is observed, which is very unlike ${}^{87}\mathrm{Rb}$ systems.     

Modeling Wormholes Generated by Dark Matter Galactic Halos in f(R)$f(R)$ Modified Gravity

Wormholes (WHs) are hypothetical topologically non-trivial spacetime structures that can be freely traversed by observers and connect two asymptotic regions or infinities. From the current theoretical development, the prospect of their existence is challenging but cannot be excluded. In this paper, generalized Ellis–Bronikov (GEB) traversable WH geometries for static and spherically symmetric spacetime in the background of $f(R)$ gravity is explored. First, the Tsujikawa-like $f(R)$ model and the shape function for the GEB model is considered, which depend on a sequence of simple Lorentzian WHs with two parameters: a free even integer exponent, n, besides the throat radius, r₀. One also consider that these WHs are generated by dark matter galactic halos (DMGHs), based on the three most common phenomenological models, viz., Navarro–Frenk–White (NFW), Thomas–Fermi (TF), and pseudo-isothermal (PI). In this concern, the satisfaction of the energy conditions (ECs) which are dependent on the dark matter (DM) models, viz., dominant energy condition (DEC) and strong energy condition (SEC) and those which are not dependent viz., null energy condition (NEC) and WEC at the WH throat and its neighborhood is investigated. Finally, the presence of exotic matter is confirmed by the violation of the NEC in all cases, revealing the supremacy and physical acceptability to support the existence of the WHs and making them compatible and traversable in Tsujikawa's-like $f(R)$ model.     

Measurement of the Ratio between g‐Factors of the Ground States of 87Rb and 85Rb

The ratio between the Landé g‐factors of the ${}^{87}$Rb $F=2$ and ${}^{85}$Rb $F=3$ ground‐state hyperfine levels is experimentally measured to be $g_F(87)/g_F(85)=1.4988586(1)$, consistent with previous measurements. The g‐factor ratio is determined by comparing the Larmor frequencies of overlapping ensembles of ${}^{87}$Rb and ${}^{85}$Rb atoms contained within an evacuated, antirelaxation‐coated vapor cell. The atomic spins are polarized via synchronous optical pumping and the Larmor frequencies are measured by off‐resonant probing using optical rotation of linearly polarized light. The accuracy of this measurement of $g_F(87)/g_F(85)$ exceeds that of previous measurements by a factor of ≈50 and is sensitive to effects related to quantum electrodynamics.     

Transmission in Graphene through Tilted Barrier in Laser Field

The transmission of Dirac fermions in graphene through a tilted barrier potential in the presence of a laser field of frequency ω is studied. By using Floquet theory, the Dirac equation is solved and then the energy spectrum is obtained. The boundary conditions together with the transfer matrix method allow to determine the transmission probabilities corresponding to all energy bands $E+l\hslash \omega$ $(l=0,\pm 1,\text{…})$. By limiting to the central band $l=0$ and the two first side bands $l=\pm 1$, it is shown that the transmissions are strongly affected by the laser field and barrier. Indeed, it is found that the Klein effect is still present, a variety of oscillations are inside the barrier, and there is essentially no transmission across all bands.