Journal of the Korean Physical Society最新文献

The crystallization of the liquid Sn tip following vapor–liquid–solid (VLS) growth of Sn–ITO nanostructures, presents an intriguing problem due to the confinement by the bottom substrate and side ITO wall. We investigated the crystalline structure and morphology of the Sn tips grown by VLS on c-plane sapphire using Bragg coherent diffraction imaging (BCDI) with a nanoscale spatial resolution in three dimensions. BCDI reconstructions of individual Sn tips reveal that each one is a single crystal with a high degree of crystalline order. Each tip maintains an overall spherical morphology—reminiscent of a liquid droplet—truncated at its base and one side. Despite this, distinct crystalline facets are identified on the crystal surface. Furthermore, a defective region was observed near the tip–substrate interface, characterized by high strain and reduced crystalline order.

This paper presents hardware and circuit-level enhancements to the programmable logic controller (PLC)-based control system for 51 high-power pulse modulators at the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) facility. The system addresses two critical operational challenges: severe electromagnetic interference (EMI) from thyratron switching and stringent dynamic interlock response-time requirements in a 60 Hz environment. An Analog Signal Filter Module (ASFM) was developed to convert noisy analog signals (beam voltage, beam current, and end-of-line clipper current) into stable DC outputs via multi-point sampling. The entire signal processing cycle is completed within approximately 11 µs. To meet the critical interlock response requirement of less than 2 ms, conventional mechanical relay modules were replaced with custom high-speed optical converter boards employing TLP620 photocouplers, and analog-to-digital conversion timing was optimized. These modifications reduced the total interlock response time from 15.4 ms to approximately 1.7 ms, ensuring rapid shutdown of the capacitor-charging power supply upon fault detection. The integrated solution improves operational reliability, stability, and safety while providing a cost-effective alternative to standalone high-speed interlock hardware. However, the system’s performance is currently validated primarily under 60 Hz operation; scalability to higher repetition rates and the long-term reliability of the optical components under continuous EMI exposure remain limitations that require future investigation.

We present a first-principles study of Fe(NO(_3))(_3)-functionalized monolayer germanene, focusing on its structural stability, electronic structure, magnetism, and spin-dependent thermoelectric transport. Fe(NO(_3))(_3) is weakly adsorbed on germanene and preserves the buckled honeycomb lattice, indicating a physisorption-dominated interaction. Nevertheless, interfacial charge transfer produces moderate p-type doping and induces a total magnetic moment of 4.3 (mu _B), mainly localized on the Fe atom. Bader charge analysis confirms a net electron transfer of about 0.71 e from germanene to Fe(NO(_3))(_3), with stronger charge depletion in the upper Ge sublayer near the adsorption interface. Band-unfolding and projected density of states analyses show that the Dirac cone of germanene is largely retained, while Fe-derived spin-polarized 3d states emerge near the Fermi level. These electronic changes lead to spin-dependent transport coefficients, a modified Seebeck response, and enhanced (PF/tau ) and electronic figure of merit (ZT_e). The results highlight superhalogen adsorption as a noncovalent strategy for introducing coupled charge-transfer, magnetic, and spin-dependent thermoelectric functionalities into germanene.

We study the index of (mathcal {N}=4) Yang–Mills theory on (S^3times mathbb {R}) at large angular momenta. A generalized Cardy limit exhibits macroscopic entropy at large N. Our result is derived using free QFT analysis, and also a background field method on (S^3). The index sets a lower bound on the entropy. It saturates the Bekenstein–Hawking entropy of known supersymmetric AdS(_5) black holes, thus accounting for their microstates. We further analyze the so-called MacDonald index, exploring small black holes and possibly new black holes reminiscent of hairy black holes. Finally, we study aspects of large supersymmetric AdS(_7) black holes, using background field method on (S^5) and ’t Hooft anomalies.

We hereby report the hitherto unexplored optical properties of the Fe₂Mn₂O₇ (FMO) pyrochlore compound synthesized by the solid-state reaction route. The compound parades a monoclinic structure when confirmed by the X-ray diffraction patterns. The optical energy band gap of the material was calculated from the reflectance spectrum and was found to be 1.83 eV. This compound showed higher reflectance in the UV range in comparison to that in the visible region. This makes this compound an effective candidate for blocking the harmful UV portion of the electromagnetic spectrum, which is hazardous to human health. Analysis of the extinction coefficient (k), skin depth (δ), and refractive index (n) over 200–800 nm reveals that FMO displays strong optical activity in the UV region while showing weaker interaction with visible light. These characteristics underscore its potential for UV-blocking applications and its applicability in optical and photocatalytic systems. In the study, the real and imaginary components of the dielectric constant, as well as the loss factor, were estimated and discussed. The photocatalytic performance was evaluated by monitoring the degradation of rhodamine B (RhB) in aqueous solution using FMO under visible-light irradiation, where the material achieved an 80.35% degradation efficiency under sunlight.

The vortex pinning and vortex dynamics of Nb–InAs composite thin films containing vertically aligned InAs nanorods were systematically investigated using combined analyses of pinning force scaling and activation energy. The field dependence of the activation energy U_eff exhibits two distinct regimes, characterized by relatively weak field dependence at low fields and significantly stronger field dependence at higher fields. The corresponding exponent α increases from values close to unity at low fields to substantially larger values at higher fields, suggesting a crossover in vortex dynamics. Dew–Hughes scaling analysis further indicates that a single-component description is insufficient to reproduce the full field dependence of the normalized pinning force density, particularly in the high-field region where the decrease in pinning force becomes more gradual. This behavior is more consistently described using a two-component model with peak positions near b ≈ 0.35 and b ≈ 0.6, implying the coexistence of different pinning characteristics. The overall results suggest that the pinning force scaling mainly reflects static pinning characteristics, while U_eff provides complementary information on vortex dynamics in Nb–InAs composite thin films.

We investigate a bilayer system of ({}^{87})Rb Rydberg atoms composed of (3times 3) and (2times 2) sublattices to study dynamics and quantum correlations between layers in a controlled three-dimensional geometry. Using time-resolved measurements, we observe Rydberg-mediated interactions between atoms in different layers. The measured dynamics are analyzed by fitting the experimental results to numerical simulations based on a theoretical model described by a Lindblad master equation, allowing reconstruction of the system’s density matrix. We evaluate the mutual information between the two sublattices and demonstrate that it provides an effective measure of interlayer correlations, even in the presence of dissipation. Our results establish a minimal and controllable platform for exploring quantum phases, frustration, and topological order in bilayer and multilayer quantum systems, advancing our understanding of strongly correlated many-body physics and higher-dimensional quantum simulators.

Density functional theory (DFT) serves as a first-principles calculation to thoroughly investigate the stability of the structure and analyze the thermoelectric, thermodynamic, electronic, and optical characteristics of the 2D BiOCl structure. The computation of formation energy, along with phonon dispersion and ab initio molecular dynamics (AIMD) outcomes, confirms the structural, dynamical, and thermal stability of the BiOCl material, respectively. The power factor is improved by a large Seebeck coefficient and relatively low electronic thermal conductivity, indicating the energy conversion capability of the material. The BiOCl behaves as a semiconductor with a 2.84 eV band gap (BPE) and 3.81 eV (HSE06) according to its electronic band structure and partial density of state (PDOS) analysis. Optical analysis of BiOCl reveals strong interactions in the range of visible to ultraviolet. BiOCl has high heat capacity because of the high phonon density of states, suggesting that it has superior thermal energy storage capability. It has comparatively poor lattice thermal conductivity. The increase in entropy and the stabilization of heat capacity at high temperatures indicate a shift towards a more disordered state. The results offer important insights into the potential of BiOCl for thermal management and optoelectronic applications.

The occurrence of ion-acoustic solitons (IASs) in a multicomponent unmagnetized plasma consisting of relativistic positive ions, relativistic negative ions, and non-isothermal electrons has been studied through modified Korteweg–de Vries (mKdV) equation by utilizing reductive perturbative method (RPM). The higher-order relativistic effects for (gamma_{i,j} approx Oleft( {frac{{v_{i,j}^{4} }}{{c^{4} }}} right)) as well as more pronounced relativistic effects for (gamma_{i,j} approx Oleft( {frac{{v_{i,j}^{6} }}{{c^{6} }}} right)) in the relativistic effects (gamma_{i,j} = left( {1 - frac{{v_{i,j}^{2} }}{{c^{2} }}} right)^{{ - frac{1}{2}}}) of positive and negative ions are seen to play an important role in the formation of solitons in the warm plasma. Further, the fast and slow compressive solitons are shown to exist in both the situations (Q^{prime})(negative to positive ion mass ratio) greater and less than one for (sigma_{i}) (positive ion to electron temperature ratio), (> sigma_{j}) (negative ion to electron temperature ratio), and (sigma_{i} < sigma_{j}). The relativistic effect (gamma_{i,j} approx Oleft( {frac{{v_{i,j}^{6} }}{{c^{6} }}} right)) demonstrates higher amplitude of the solitons than the relativistic effect (gamma_{i,j} approx Oleft( {frac{{v_{i,j}^{4} }}{{c^{4} }}} right)). This model can be employed to explore the dynamics of plasmas in various contexts, including both astrophysical and laboratory settings.

In this research, a novel correlation between the radiation force and sound power in an obliquely focused ultrasonic field is proposed based on a ray acoustic model. Meanwhile, the ray acoustic model is employed to derive the numerical solution for calculating the radiation force of the obliquely focused beam. Through numerical simulation, the effects of the transducer elements of the spherical focusing probe array on target parameters, half-aperture angle, and incident angle are theoretically investigated. Additionally, a comparative analysis of the performance between the established model and the far-field integration model is conducted, and the results demonstrate that the radiation forces exerted by the two models on fully absorbing targets under different half-aperture angles are relatively consistent. This verifies that the ray acoustic model is also highly effective in the sound power correction measurement of obliquely focused beams. Furthermore, the integration model derived in this study features the simplicity of a single integral, making it more convenient in practical applications and promising for wider utilization in future practices.