Altermagnets present a class of fully compensated collinear magnetic order, where the two sublattices are not related merely by time-reversal combined with lattice translation or inversion, but require an additional lattice rotation. This distinctive symmetry leads to a characteristic splitting of the magnon bands; however, the splitting is only partial—residual degeneracies persist along certain lines in the Brillouin zone as a consequence of the underlying altermagnetic rotation. We consider a two-dimensional d -wave altermagnetic spin model on the checkerboard lattice and introduce additional interactions such as an external magnetic field and Dzyaloshinskii-Moriya interactions that lift these degeneracies. The resulting magnon bands become fully gapped and acquire nontrivial topology, characterized by nonzero Chern numbers. We demonstrate the crucial role of altermagnetism for the generation of the Berry curvature. As a direct consequence of the topological magnons, we find finite thermal Hall conductivity κ x y , which exhibits a characteristic low-temperature scaling, κ x y ∝ T 4 . Moreover, κ x y changes signs under reversal of the magnetic field, exhibiting a sharp jump across zero field at low temperatures. We also demonstrate topologically protected chiral edge modes in a finite strip geometry.

Heat transfer is a critical aspect of modern electronics, and a deeper understanding of the underlying physics is essential for building faster, smaller, and more powerful devices with improved performance and efficiency. In such nanoscale structures, the heat transfer between two materials is limited by the finite thermal boundary conductance across their interface. Using ultrafast electron diffraction under grazing incidence we investigated the heat transfer from ultrathin epitaxial Pb films to an Si(111) substrate under strong nonequilibrium conditions. Upon applying an intense femtosecond laser pulse, the 5–7 ML thin Pb film undergoes rapid heating by 10–120 K while the Si substrate remains cold at ≈10 K. At such large temperature discontinuities, a significantly faster cooling is observed for more strongly excited Pb films. The decrease in the corresponding cooling time constant is explained by variations in thermal boundary conductance, interpreted within the framework of the diffuse mismatch model. The thermal boundary conductance is reduced by more than a factor of three in comparison with Pb films grown on H-terminated substrates, underscoring the importance of substrate, heterofilm, and interface morphologies.

Oil–water emulsions resist aggregation due to the presence of negative charges at their surface that leads to mutual repulsion between droplets, but the molecular origin of oil charge is currently under debate. Although much evidence has suggested that ionic species must accumulate at the interface, an alternative perspective attributes the negative charge on the oil droplet to charge transfer of electron density from water to oil molecules. Although the charge transfer mechanism is consistent with the correct sign of oil charge, it is just as important to provide good estimates of the charge magnitude to explain emulsion stability and electrophoresis experiments. Here, we show using energy decomposition analysis that the amount of net flow of charge from water to oil is negligibly small due to nearly equal forward and backward charge transfer through weak oil–water interactions, such that oil droplets would be unstable and coalesce, contrary to experiment. The lack of charge transfer also explains why vibrational sum frequency scattering reports a blue shift in the oil C–H frequency when forming emulsions with water, which arises from Pauli repulsion due to localized confinement at the interface. Finally, unlike ions, neither charge transfer nor dynamic polarization can produce a finite conductivity needed to couple to electric fields that would explain electrophoretic mobility.

Abstract Oil–water emulsions resist aggregation due to the presence of negative charges at their surface that leads to mutual repulsion between droplets, but the molecular origin of oil charge is currently under debate. Although much evidence has suggested that ionic species must accumulate at the interface, an alternative perspective attributes the negative charge on the oil droplet to charge transfer of electron density from water to oil molecules. Although the charge transfer mechanism is consistent with the correct sign of oil charge, it is just as important to provide good estimates of the charge magnitude to explain emulsion stability and electrophoresis experiments. Here, we show using energy decomposition analysis that the amount of net flow of charge from water to oil is negligibly small due to nearly equal forward and backward charge transfer through weak oil–water interactions, such that oil droplets would be unstable and coalesce, contrary to experiment. The lack of charge transfer also explains why vibrational sum frequency scattering reports a blue shift in the oil C–H frequency when forming emulsions with water, which arises from Pauli repulsion due to localized confinement at the interface. Finally, unlike ions, neither charge transfer nor dynamic polarization can produce a finite conductivity needed to couple to electric fields that would explain electrophoretic mobility.

The Katz-Sarnak philosophy states that statistics of zeros of L-function families near the central point as the conductors tend to infinity agree with those of eigenvalues of random matrix ensembles as the matrix size tends to infinity. While numerous results support this conjecture, S. J. Miller observed that for finite conductors, very different behavior can occur for zeros near the central point in elliptic curve L-function families. This led to the creation of the excised model of Dueñez, Huynh, Keating, Miller, and Snaith, whose predictions for quadratic twists of a given elliptic curve are well fit by the data. The key ingredients are relating the discretization of central values of the L-functions to excised matrices based on the value of the characteristic polynomials at 1 and using lower order terms in the one-level density and pair-correlation statistics to adjust the matrix size. We extended this model to a family of twists of an L-function associated to a given holomorphic cuspidal newform of odd prime level and arbitrary weight. We derive the corresponding “effective” matrix size for a given form by computing the one-level density and pair-correlation statistics for a chosen family of twists, and we show there is no repulsion for forms with weight greater than 2 and principal nebentype. We experimentally verify the accuracy of the model, and as expected, our model recovers the elliptic curve model. Further, we uncover anomalous deviation from the expected symmetry for twists of forms with unitary symmetry.

This article presents an examination of a two-dimensional, non-Hermitian Su–Schrieffer–Heeger model, which differs from its conventional Hermitian counterpart by incorporating gain and/or loss terms, mathematically represented by imaginary on-site potentials. The time-reversal symmetry is disrupted due to these on-site potentials. Exceptional points in a non-Hermitian system feature eigenvalue coalescence and non-trivial eigenvector degeneracies. Utilization of the rank-nullity theorem and graphical analysis of the phase rigidity factor enables identification of true exceptional points. Furthermore, this investigation achieves vectorized Zak phase quantization and examines a topolectric resistors–inductors–capacitors circuit to derive the corresponding topological boundary resonance condition and the quantum Hall susceptance. Although Chern number quantization is not feasible, staggered hopping amplitudes corresponding to unit-cell lattice sites lead to broken inversion symmetry with non-zero Berry curvature, resulting in finite anomalous Nernst conductivity.

Background. Periodic layered systems have recently attracted researchers and engineers due to their possible wide applications in nanoelectronics. In such systems, in addition to their direct use as a periodic structure, various defects can be studied. Against the background of an ideal periodic structure, reflection from a structure with a defect allows one to obtain important information about the defect itself. Of particular interest is the use of circularly polarized light for these purposes. Aim. The paper presents the results of calculations of the angular spectra of ellipsometric parameters from a periodic structure with a defect. The latter uses a dielectric layer and a layer with finite conductivity. Methods. Spatial. The work uses the ellipsometric method for analyzing the optical properties of material media. Using the method of characteristic matrices, the ellipsometric parameters of circularly polarized light reflected from the layered system are calculated. Results. The work notes the non-equivalence of the calculation results for different locations of the defect - the ellipsometric parameters of the reflected light significantly depend on where the defect is located inside the structure. This effect can be used to determine this location against the background of reflection from an ideal periodic structure. In addition, it has been shown that dielectric and conductive defects lead to significantly different angular spectra of ellipsometric parameters, which can also serve as a certain marker of the defect itself. Conclusion. The use of circularly polarized radiation to diagnose periodic media with defects makes it possible to obtain important information about defects against the background of an ideal periodic structure.

Quasiparticle excitations in material solids often experience a fictitious gauge field, which can be a potential source of intriguing transport phenomena. Here, we show that low-energy excitations in insulating antiferromagnetic skyrmion crystals on the triangular lattice are effectively described by magnons with an SU(3) gauge field. The three-sublattice structure in the antiferromagnetic skyrmion crystals is inherited as three internal degrees of freedom for the magnons, which are coupled to their kinetic motion via the SU(3) gauge field that arises from the topologically nontrivial spin texture in real space. We show that the noncommutativity of the SU(3) gauge field breaks an effective time-reversal symmetry and contributes to a magnon thermal Hall effect. We further demonstrate the emergence of the finite thermal Hall conductivity in the antiferromagnetic skyrmion crystals by the linear spin-wave theory. The possible impact of different gauge structures on a thermal Hall conductivity is also discussed.

Effective control of terahertz radiation requires fast and efficient modulators with a large modulation depth—a challenge that is often tackled by using metamaterials. Metamaterial-based active modulators can be created by placing graphene as a tuneable element shunting regions of high electric field confinement in metamaterials. However, in this common approach, the graphene is used as a variable resistor, and the modulation is achieved by resistive damping of the resonance. In combination with the finite conductivity of graphene due to its gapless nature, achieving 100% modulation depth using this approach remains challenging. Here, we embed nanoscale graphene capacitors within the gaps of the metamaterial resonators, and thus switch from a resistive damping to a capacitive tuning of the resonance. We further expand the optical modulation range by device excitation from its substrate side. As a result, we demonstrate terahertz modulators with over four orders of magnitude modulation depth (45.7 dB at 1.68 THz and 40.1 dB at 2.15 THz), and a reconfiguration speed of 30 MHz. These tuneable capacitance modulators are electrically controlled solid-state devices enabling unity modulation with graphene conductivities below 0.7 mS. The demonstrated approach can be applied to enhance modulation performance of any metamaterial-based modulator with a 2D electron gas. Our results open up new frontiers in the area of terahertz communications, real-time imaging, and wave-optical analogue computing.

We study the effects of the oscillating axion field present in our environment on the Casimir pressure between two metallic plates. We take into account the finite conductivity of the boundary plates and model the interactions between matter and photons in the Schwinger-Keldysh formalism. This allows us to take into account dissipation in the quantum field description of this open quantum system and retrieve the Lifschitz results for the Casimir interaction between two metallic plates. We then compute the leading correction to the Lifschitz theory in inverse powers of the axion suppression scale and show that the Casimir pressure receives oscillating corrections depending on the product of the axion mass and the distance between the plates. This contribution is repulsive at large distance compared to the axion Compton wavelength as a consequence of the breaking of parity invariance by the axion dark matter background. Published by the American Physical Society 2025

In areas with frequent lightning activity, studying lightning induced voltage on overhead distribution lines is crucial to improve the line performance under nearby lightning strikes. This article studies the impact of ground losses in the transmission line model on lighting-induced voltage using an analytical approach. The soil characteristics was represented using fixed and frequency dependent soil models. Firstly, the lightning electromagnetic fields have been computed considering the influence of finite ground conductivity using Cooray-Rubinstein model. Afterwards, the lightning-induced voltage has been computed using Agrawal coupling model in frequency domain. The results show that incorporating ground losses in the transmission line model has a considerable effect on lightning-induced voltages at different velocities. The influence of velocity was evaluated at: 40 m/μs, 120 m/μs, and 200 m/μs respectively. It was found that the influence of ground losses on the peak value of LIVs is more significant at 40 m/μs. Since the median value of lightning velocities is 120 m/μs, it is deduced that the influence of ground losses is more pronounced at lower velocities as it causes an increase in the magnitude of lightning-induced voltage. The effect of incorporating ground losses in the transmission line model on lightning-induced voltage is also evaluated at various values of transmission line height. The effect of transmission line height was examined at 6 m and 10 m respectively. It was found that the effect of ground losses is greater at the height of 10 m at the midpoint of the transmission line. Consequently, as the height of the transmission line decreases, the influence of ground losses also decreases. However, the opposite occurs at positions far from the midpoint, where the influence of ground losses increases with lower transmission line heights. The impact of incorporating ground losses in the transmission line model on lightning-induced voltage is examined at different distances between the lightning channel and the transmission line. The effect of these distances was examined at values of 50 m and 100 m respectively. It was found that the influence of ground losses diminishes at distances of 100 m and above. Furthermore, lightning induced voltage magnitude with frequency dependent soil model is lower than with fixed soil model.

We study the large-scale co-evolution of the system of currents, magnetic fields, and density perturbations arising from pulsed rf plasma heating using a loop antenna in the experiments at the Krot plasma device. Localized heating of electrons by a short rf pulse leads to redistribution of magnetized plasma particles in a fast, so-called unipolar (non-ambipolar) regime, which is accompanied by the excitation of eddy electric currents [Aidakina et al., “Experimental demonstration of the “unipolar cell” dynamics in a large laboratory magnetoplasma,” Phys. Plasmas 31, 122110 (2024)]. The pulsed currents generated in the plasma can propagate over large distances from the source in the form of low-frequency waves. It is shown that the parallel transport of the currents and magnetic field perturbations occurs at the velocity of whistler waves, whose dispersion is determined by the characteristic time of electron heating, i.e., the duration of the rf pulse and its edges. The perpendicular dynamics of the currents and magnetic fields in a dense and collisional plasma is diffusive due to the finite conductivity determined by Coulomb collisions. Density perturbations arising from electron heating propagate at significantly lower (ion sound) velocities. The experiments performed demonstrate the possibility of nonlinear generation of pulsed whistlers using a compact antenna excited by a short rf pulse.

The capability of cathode interlayer (CIL) in regulating the conductivity, interfacial dipole, and work function of the electrode plays a critical role in determining the photovoltaic performance of organic solar cells (OSCs). The widely used perylene-diimide-based CILs suffered from the inbuilt limitation of finite conductivity and poor thickness tolerance. To address this issue, we develop a universal strategy to finely optimize the functionality of perylene-diimide-type CIL (PDINN) by incorporating polyfluorine-substituted copper phthalocyanine (CuPc) derivative to form a hybrid CIL. It is found that the hydrogen bonding and π-π interaction between PDINN and CuPc can address the solvent processability issue of CuPc used as CIL. The incorporation of CuPc in the PDINN layer leads to better film morphology, increased conductivity, and reduced cathode work function, enabling greater CIL thickness tolerance and significantly improved photovoltaic performance of OSCs. Notably, the PM6:D18:L8-BO-based device using PDINN:F16CuPc as hybrid CIL yields a remarkable power conversion efficiency (PCE) of 20.17%, which is a significant improvement with regard to the PCE of 19.29% for the control device based on PDINN CIL. Particularly, this strategy demonstrates a universality in multiple photoactive layers and various perylene-diimide-based CILs, offering an effective approach to developing highly efficient OSCs.

Abstract The capability of cathode interlayer (CIL) in regulating the conductivity, interfacial dipole, and work function of the electrode plays a critical role in determining the photovoltaic performance of organic solar cells (OSCs). The widely used perylene‐diimide‐based CILs suffered from the inbuilt limitation of finite conductivity and poor thickness tolerance. To address this issue, we develop a universal strategy to finely optimize the functionality of perylene‐diimide‐type CIL (PDINN) by incorporating polyfluorine‐substituted copper phthalocyanine (CuPc) derivative to form a hybrid CIL. It is found that the hydrogen bonding and π–π interaction between PDINN and CuPc can address the solvent processability issue of CuPc used as CIL. The incorporation of CuPc in the PDINN layer leads to better film morphology, increased conductivity, and reduced cathode work function, enabling greater CIL thickness tolerance and significantly improved photovoltaic performance of OSCs. Notably, the PM6:D18:L8‐BO‐based device using PDINN:F16CuPc as hybrid CIL yields a remarkable power conversion efficiency (PCE) of 20.17%, which is a significant improvement with regard to the PCE of 19.29% for the control device based on PDINN CIL. Particularly, this strategy demonstrates a universality in multiple photoactive layers and various perylene‐diimide‐based CILs, offering an effective approach to developing highly efficient OSCs.

In light of recent experimental data indicating a substantial thermal Hall effect in square lattice antiferromagnetic Mott insulators, we investigate whether a simple Mott insulator can sustain a finite thermal Hall effect. We verify that the answer is "no" if one performs calculations within a spin-only low-energy effective spin model with noninteracting magnons. However, by performing determinant quantum MonteCarlo simulations, we show the single-band t-t^{'}-U Hubbard model coupled to an orbital magnetic field does support a finite thermal Hall effect when t^{'}≠0 and B≠0 in the Mott insulating phase. We argue that the (carrier agnostic) necessary conditions for observing a finite thermal Hall effect are time-reversal and particle-hole symmetry breaking. By considering magnon-magnon scattering using a semiclassical Boltzmann analysis, we illustrate a physical mechanism by which finite transverse thermal conductivity may arise, consistent with our symmetry argument and numerical results. Our results indicate that square and triangular lattices with SU(2) symmetry can support a finite thermal Hall effect and call for a critical reexamination of thermal Hall effect data in insulating magnets, as the magnon contribution should not be excluded apriori.

This paper presents 3D modeling for lightning electromagnetic effects to analyze the peak induced voltages on overhead conductors using the finite element method (FEM) and COMSOL Multiphysics software. It mainly focuses on the parameters that affect the peak induced voltage of overhead conductors, such as the height of the conductor from the ground, the conductivity of the ground, and the speed of the source current. Initially, a thorough observation of the return stroke current for lightning strikes to flat ground at different heights along the lightning channel and induced voltage at the center point of the horizontal conductor at distances of 40 m, 60 m, and 100 m from the stroke point has been carried out for model validation. Then the effect of conductor height on the peak induced voltages on overhead conductors, with specific numerical results (e.g., peak induced voltage reaching 75.70 kV at the center point and − 14.87 kV at the terminal point for the 50 m horizontal distance from the stroke point, 4.8 m lower conductor height, and finite ground). It observed that there is a significant impact on peak induced voltages at the center and terminal points at different conductor heights for finite ground conductivity. The findings also show that for finite ground conductivity (0.001 Sm−1), the peak induced voltage at the center point is more than twice the value observed in a perfectly electric conducting ground (5.98 × 107 Sm−1) at a 4.8 m lower conductor height.

Competition between stationary and oscillatory thermocapillary convection of a Cattaneo–Christov fluid over a thick wall with finite thermal conductivity

This paper explores nanodiode and nanotriode structures with incorporated dielectric films in vacuum electronics. Such emission structures allow for very high (on the order of 1012A/m2 and more) current densities and differ greatly from conventional field emitters. For all structures considered, we derive the electrostatic Green’s function, construct potential barrier profiles, calculate tunneling coefficients, and determine the volt–ampere (VAC) characteristics, taking into account the distribution of electron energies. This work presents novel results, including a precise formula for the potential distribution in a structure with a dielectric film. This formula accounts for the finite conductivity of the semiconductor film and incorporates the reverse tunnel current within the structure. Considering this effect in nanostructures is crucial, particularly at low anodic voltages.

Radiation Pressure-Driven Magneto-Gravitational Instability in Finitely Conducting Strongly Coupled Quantum Plasmas

Let [Formula: see text] be a commutative ring graded by an arbitrary commutative cancellation monoid [Formula: see text]. We say that [Formula: see text] is a graded finite conductor ring if [Formula: see text] and [Formula: see text] are finitely generated for every homogeneous elements [Formula: see text] of [Formula: see text]. In this paper, we generalize several results on finite conductor rings to graded finite conductor rings. We then study the possible transfer of this property to the graded trivial ring extension and the graded amalgamation. Our goal is to provide examples of new classes of [Formula: see text]-graded rings that satisfy the above property.