The spin-S Heisenberg antiferromagnet on the two-dimensional lattice is investigated for S=1/2 and S=1. We consider interaction at isolated dimers ($J_{\rm d}$) and interaction bonds that form the bounce lattice ($J_{\rm b}$). For $J_{\rm d}=J_{\rm b}$, the system is reduced to the maple-leaf-lattice antiferromagnet. We primarily conduct highly parallelized numerical diagonalization to examine the spin excitation gap above the ground state for various $J_{\rm b}/J_{\rm d}$ cases. For S=1/2, we report calculations for a 42-site cluster that has not been previously treated. The S=1 case is examined for the first time for clusters up to 24 sites. Regardless of whether S=1/2 or 1, we find that the system has a gapped nature for small $J_{\rm d}/J_{\rm b}$ and becomes gapless at $J_{\rm d}/J_{\rm b}\sim 1.4$. For S=1, we also find that another gapped region appears between the gapless case at $J_{\rm d}/J_{\rm b}\sim 1.4$ and the boundary of the exact-dimer phase.
We study the temperature dependence of the thermodynamic properties of spin-1/2 antiferromagnets on two-dimensional lattices. Our analysis employs the sine-square deformation (SSD), in which a real-space envelope function is applied to the Hamiltonian so that the local energy scale is smoothly reduced to zero at the system boundaries. The quantum eigenstates of the SSD Hamiltonian exhibit bulk-like behavior near the system center, effectively mimicking the thermodynamic limit even in small finite-size calculations. Using these fictitious bulk states, we compute the energy density, specific heat, and magnetic susceptibility as functions of temperature. We find that both the triangular- and kagome-lattice antiferromagnets show either a shoulder or a pronounced double-peak structure in the low-temperature specific heat, whereas the kagome case particularly shows a strong enhancement of magnetic susceptibility down to the lowest temperature range. These direct comparisons, together with the square-lattice and one-dimensional cases, reveal that although both frustrated systems retain a substantial amount of entropy, the low-energy excitations below ~ 0.5J of the kagome lattice are predo
Antiferromagnets have attracted significant attention because of their considerable potential in engineering high-density and ultrafast memory devices, a crucial and increasingly demanded component of contemporary high-performance information technology. Theoretical and experimental investigations are actively progressing to provide the capability of efficient switching and precise control of the Néel vector, which is crucial for the intended practical applications of antiferromagnets. Recently, a time-dependent Schwinger boson mean-field theory has been successfully developed to study the sublattice magnetization switching in anisotropic quantum antiferromagnets [K. Bolsmann $et \, al.$, \textcolor{blue}{\hyperlink{10.1103/PRXQuantum.4.030332}{PRX Quantum $\mathbf{4}$, 030332 (2023)}}]. Here we use a complementary exact diagonalization method to study such sublattice magnetization switching, but in small-cluster quantum antiferromagnets, by means of an external magnetic field. Furthermore, this article aims to support the findings of the Schwinger boson approach. We show that the results of both approaches are consistent at short time scales, with only about 12.5 $\%$ deviations.
In classical physics, there is a basic principle, namely "A particle cannot be located at the position of another one on the same time". Which consequences can be derived if this principle is transferred into quantum physics? For doing that, two distinguishable particles are considered to be trapped in a potential box by means of the Schrödinger equation. In result, the particles can necessarily be located only at discrete positions.
We study the Heisenberg antiferromagnet on the maple-leaf lattice using several numerical approaches, focusing on the numerical linked-cluster expansion (NLCE), which exhibits an unconventional convergence extending to low and even zero temperatures. We evaluate thermodynamic properties as well as spin-spin correlations through the equal-time structure factor. Within NLCE the specific heat capacity reveals a two-peak structure at $T_1 \approx 0.479\,J$ and $T_2 \approx 0.131\,J$, reminiscent of the corresponding result for the triangular lattice. At intermediate temperatures, the spin-spin structure factor develops features that reflect the absence of reflection symmetry in the lattice. The zero-temperature convergence of NLCE enables reliable estimates of the ground-state energy and points to a short-range correlated paramagnetic ground state composed of resonating hexagonal motifs. The NLCE results are benchmarked against Pseudo-Majorana Functional Renormalization Group, finite-temperature Lanczos, and classical Monte Carlo simulations.
We investigate flat magnonic bands in a generalized sawtooth-chain model in which three sets of exchange parameters (symmetric Heisenberg exchange, axial Ising anisotropy, and antisymmetric Dzyaloshinskii-Moriya (DM) exchange) are assigned independently to each side of the triangular plaquette. If the effective Dzyaloshinskii-Moriya (DM) interaction parameters are generated via the Katsura-Nagaosa-Balatsky (KNB) mechanism of magnetoelectricity, they become explicit functions of the electric-field magnitude and direction, as well as of the lattice geometry, which in the present casen is characterized by two bond angles. We focus on the situation in which these two angles are unequal, corresponding to a distortion of the triangular plaquette. Several electric-field induced flat-band scenarios in the distorted sawtooth chain are analyzed, and expressions are derived for the electric-field strength required to drive the one-magnon excitations into a flat-band regime when the field is aligned along the lattice bonds. The saturation field and its dependence on the distortion angle are also examined. Finally, we establish a mapping between the flat-band solutions for a general DM interact
Typicality is a well-established and very general property of quantum many-body systems, referring to the phenomenon that the expectation values of any given observable are practically indistinguishable for the overwhelming majority of all pure states (normalized vectors) in a sufficiently high-dimensional Hilbert (sub-)space. Here, we provide very simple and general arguments that analogous typicality properties of pure states (phase space points) in classical many-body systems are still expected to hold true for macroscopic observables, but not any more for microscopic (few-body) observables.
The relaxed state of a magnetized relativistic hot plasma composed of inertial electrons and positrons having different relativistic temperatures and a fraction of static positive ions is studied. From the steady-state solutions of vortex dynamics equations and the relation for current density, a non-force-free triple Beltrami (TB) relaxed state equation is derived. The TB state is characterized by three scale parameters that consequently provide three different self-organized structures. The analysis of the relaxed state shows that for specific values of generalized helicities, the disparity in relativistic temperature and the existence of a small fraction of static positive ions in pair plasma can transform the nature of scale parameters. Moreover, an analytical solution of the TB state for an axisymmetric cylindrical geometry with an internal conductor configuration demonstrates that due to asymmetries of temperature and density of plasma species, diamagnetic structures can transform into paramagnetic ones and vice versa. The present study will improve our understanding of pair plasmas in trap-based plasma confinement experiments and astrophysical environments.
We consider the $S=1/2$ Heisenberg antiferromagnet on the Tasaki square lattice (flat-band spin system) and study its low-temperature thermodynamics around the saturation magnetic field. To this end, we construct a mapping of the ground states in the subspaces with total $S^z=N/2,\ldots,N/3$ ($N$ is the number of lattice sites) on the hard squares on an auxiliary square lattice and use classical Monte Carlo simulations to examine the latter classical system. The most prominent feature of the $S=1/2$ Heisenberg antiferromagnet on the Tasaki square lattice is an order-disorder phase transition which occurs at a low temperature just below the saturation magnetic field and belongs to the 2D Ising universality class.
The neutron capture rates and Maxwellian averaged cross sections (MACS) for 90Zr(n,γ) 91Zr and 92Zr(n,γ) 93Zr processes have been computed within the framework of Talys v1.96. The effects of phenomenological nuclear level density (NLD) parameters and the gamma strength functions (GSFs) on Maxwellian averaged cross sections and neutron capture rates are examined both quantitatively and qualitatively. The present model based computed data for MACS and reaction rates gives a good comparison with the existing literature. The fine-tuning of the statistical models nuclear properties (level density and gamma-ray strength) to reproduce experimental data will allow the detailed investigation of the s process network.
The neutron optical Lloyd interferometer can serve as a potent experiment for probing fundamental physics beyond the standard models of particles and cosmology. In this article, we provide a full Green's function analysis of a Lloyd interferometer in the limit that the reflecting mirror extends to the screen. We consider two distinct situations: first, we will review the theoretical case of no external fields being present. Subsequently, we will analyze the case in which a gravitational field is acting on the neutrons. The latter case provides the theory necessary for using a Lloyd interferometer as a probe of gravitational fields.
The quantum-phase-field concept of matter is revisited with special emphasis on the introverted view of space. Extroverted space surrounds physical objects, while introverted space lies in between physical objects. Space between objects leads to a network structure of matter: a network in which one-dimensional space filaments connect massive elementary particles. Missing quantum fluctuations in the finite space filaments are interpreted as `gravitons,' the exchange particles of gravitational attraction between elementary particles.
In 2005, we proposed that the nerve pulse is an electromechanical soliton. This concept represents a challenge to the well-known Hodgkin-Huxley model which is of a purely electrical nature. The soliton theory was criticized by Nimtz and Aichmann in a recent article in Zeitung für Naturforschung A. Here, we wish to comment on some statements that we regard as misinterpretations of our views.
A compact summary of present fundamental physics is given and evaluated. Its 9 lines describe all observations exactly and contain both general relativity and the standard model of particle physics. Their precise agreement with experiments, in combination with their extreme simplicity and their internal consistency, suggest that there are no experimental effects beyond the two theories. The combined properties of the 9 lines also imply concrete suggestions for the microscopic constituents in a complete theory of relativistic quantum gravity. It is shown that the microscopic constituents cannot be described by a Lagrangian or by an equation of motion. Finally, the 9 lines specify the only decisive tests that allow checking any specific proposal for such a theory.
Building on work of Meixner [J. Meixner, Z. Naturforschung 3a, 506 (1948)], we show how to compute the exact scattering amplitude (or $T$-matrix) for electromagnetic scattering from a perfectly conducting disk. This calculation is a rare example of a non-diagonal $T$-matrix that can nonetheless be obtained in a semi-analytic form. We then use this result to compute the electromagnetic Casimir interaction energy for a disk opposite a plane, for arbitrary orientation angle of the disk, for separations greater than the disk radius. We find that the proximity force approximation (PFA) significantly overestimates the Casimir energy, both in the case of the ordinary PFA, which applies when the disk is parallel to the plane, and the "edge PFA," which applies when the disk is perpendicular to the plane.
It’s a pretty good movie, but it needed to be a great movie to thrive in an oversaturated superhero market
A new AI-powered framework could transform how astronomers measure the expansion of the Universe。 By analyzing images of Type Ia supernovae and modeling their environments in unprecedented detail, researchers can estimate cosmic distances with near-spectroscopic accuracy。 The technique is designed for the flood of data expected from the upcoming Ve
A new study suggests Earth may have been sending tiny hitchhikers to Venus for billions of years。 Researchers found that asteroid impacts could launch microbes into space, where some might survive the journey and end up suspended in Venus' clouds。 If future missions detect life there, there's a surprising chance it didn't originate on Venus at all—
Astronomers have released the largest gravitational wave catalog ever, revealing 161 new black hole collisions and pushing the total number of detections to 390。 Among the highlights are the clearest gravitational wave signal ever recorded, the most accurate location of a black hole merger, and growing evidence that some black holes are the product
Researchers have shown that ultracold atoms can be driven into a strange new quantum state called a fractional Fermi sea, where particles organize themselves in unexpected ways。 The discovery points to a new phase of matter that goes beyond established quantum theories and could expand the possibilities of quantum simulation