Matter and Radiation at Extremes

Recent advances in synthesis, structure, and properties of binary and ternary transition metal phosphides

Xinyue Wang, Xin Yang, Liyunxiao Wu, Jun Deng, Qingyang Hu, Huiyang Gou

2026, 11(4) doi: 10.1063/5.0325095

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Abstract:
Transition metal phosphides exhibit diverse crystal structures and intriguing physical properties, including superconductivity and magnetism. Despite extensive studies, obtaining a comprehensive understanding of the synthesis methods, structural variations, and emergent phenomena in binary and ternary phosphides remains an essential task. Here, we review recent progress in the synthesis, crystal structures, and physical properties of binary (e.g., Mo–P, Rh–P, Re–P, and Ir–P) and ternary (transition metal–transition metal–phosphorus, alkaline earth metal–transition metal–phosphorus, and rare earth element–transition metal–phosphorus) phosphides. Emphasis is placed on superconductivity, magnetism, and electronic structures, highlighting correlations between composition, structure, and properties. This synthesis of current knowledge provides insights into the design of novel phosphide materials and can guide future exploration of functional materials with tailored electronic and magnetic behaviors.

Long-lasting plasma density structures utilizing tailored density profiles

M. Luo, C. Riconda, A. Grassi, N. Wang, J. S. Wurtele, I. Pusztai, T. Fülöp

2026, 11(4) doi: 10.1063/5.0312402

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Abstract:
Using fully kinetic particle-in-cell simulations, we investigate the stability and performance of autoresonant plasma beat-wave excitation in plasmas with tailored density profiles. We show that a prescribed spatial variation of the background density sustains continuous phase locking between the driving laser beat and the excited plasma mode, thereby enabling precise control of the shape and group velocity of the plasma wavepacket and providing an alternative to frequency chirping of the drive lasers. The density-gradient scale is found to govern the nonlinear autoresonant growth, and the attainable saturation amplitude can exceed the classical Rosenbluth–Liu prediction and, for appropriate laser intensities, approach the nonrelativistic wave-breaking limit. We show that a four-laser configuration in a steep parabolic density profile can generate a specially confined two-phase quasi-periodic plasma lattice. The generation of such structures may lead to novel applications in plasma photonics.

Electron–positron pair generation using a single kJ-class laser pulse in a foam–reflector setup

Oliver Mathiak, Lars Reichwein, Alexander Pukhov

2026, 11(4) doi: 10.1063/5.0317574

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Abstract:
We investigate the process of creating electron–positron pairs from laser–matter interaction in pre-ionized foam targets using particle-in-cell simulations. A high-intensity laser pulse drives electrons via direct laser acceleration up to a cone-shaped reflector. The high-energy electrons interact with the reflected laser pulse, generating abundant pairs. The effects of the plasma-channel shape on the propagation of the laser pulse and subsequent pair production are studied. The results show that the number of Compton emission and Breit–Wheeler pair creation events is highly sensitive to the diffraction of the laser due to its interaction with the foam.

Ion correlation effect on electron screening of moderately coupled plasma

Fuyang Zhou, Guangwei Meng, Yizhi Qu, Yong Wu, Jianguo Wang

2026, 11(4) doi: 10.1063/5.0299045

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Abstract:
For moderately/strongly coupled plasmas, modeling of the electron screening effect remains an unresolved problem, owing to the complicated many-body correlations among the surrounding electrons and ions. In this work, we investigate the ion correlation effect on electron screening of moderately coupled plasmas using an atomic-state-dependent electron-screening model. It is found that the electron density around a target ion is significantly enhanced by the ion correlation effect from surrounding ions. By considering this ion correlation effect, the electron density fluctuation induced by the target ion becomes non-spherically symmetric, which causes traditional electron screening models to underestimate the screening effects, especially for moderately/strongly coupled and weakly degenerate plasmas. The present model and findings are validated by molecular dynamics simulations of moderately coupled ultracold neutral plasmas. For moderately coupled plasmas, the Coulomb logarithm is found to decrease by about 10%–30% owing to the ion correlation effect, which should be considered when modeling plasma effects on atomic processes, radiation transport, and thermodynamic properties.

Generation of high-yield, azimuthally spin-polarized positron beams from relativistic electrons in cone–channel targets

Yue Cao, Si-Man Liu, Kun Xue, Li-Xiang Hu, Jing-Yi Wang, Qian-Ni Li, Xin-Yu Liu, Jian-Xing Li, Tong-Pu Yu

2026, 11(4) doi: 10.1063/5.0324067

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Abstract:
High-energy, high-yield structured spin-polarized positron beams have important applications in nuclear physics, high-energy physics, and information storage. However, their generation remains a significant challenge. Here, we put forward a scheme to generate these beams using a dense relativistic electron beam interacting with a gas-filled cone–channel target. The interaction induces composite focusing fields comprising the electric field from a plasma bubble and skin-layer magnetic fields from the electron beam and displacement currents. These fields compress the seed beam to ultrahigh density, thereby inducing extreme fields that enable efficient γ-photon emission and subsequent pair production, leading to a high positron yield. Furthermore, the azimuthal topology of these fields is imprinted onto the generated positrons, creating unique azimuthal polarization. Our simulations demonstrate the generation of an azimuthally polarized positron beam with a charge of 0.63 nC, a polarization approaching 60%, and an energy conversion efficiency exceeding 3%. Our method provides a highly efficient pathway for generating azimuthally polarized positrons, paving the way for their potential applications.

High-contrast and high-resolution X-ray phase-contrast imaging based on betatron sources driven by a laser wakefield accelerator

Sijie Fan, Jiaxing Wen, Hansheng Ye, Hang Guo, Sixin Wu, Mao Peng, Gaojie Zeng, Xiangjun Xiang, Tao Zhu, Qiang Gong, Lai Wei, Shaoyi Wang, Bo Zhang, Yuchi Wu, Song Li, Xianfeng Shen, Zhentian Wang, Wentao Wang, Shuke Huang, Wenhui Huang, Zongqing Zhao

2026, 11(4) doi: 10.1063/5.0320107

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Abstract:
X-ray phase-contrast imaging (XPCI) provides superior sensitivity for the diagnosis of low-Z materials compared with absorption-based techniques. Betatron radiation generated by laser wakefield accelerators, which offers high photon flux, ultra-short duration, and relatively high spatial coherence, is a promising compact source for XPCI. At present, there is a lack of knowledge about how to control wakefield accelerators and realize high-quality XPCI. This study investigates the influence of gas pressure (plasma density) on betatron source characteristics and on the performance of propagation-based XPCI. Through particle-in-cell and wave-optics simulations, it explores the relationship between gas pressure and imaging characteristics such as spatial resolution and brightness and determines an optimal operation window. Experimental results confirm this optimal operation window at 40–45 psi [plasma density ∼3–4×1018cm−3], with which a peak photon flux of 8×1012 photons/sr and a contrast of 20.32% at a spatial resolution of 5 μm are realized. This study demonstrates a pathway for the optimization of betatron-based XPCI, enabling synchrotron-comparable spatial resolution in a laboratory-scale setup and shows the potential of XPCI in ultrafast microscopic imaging applications.

High-power, low-coherence laser pulse generation via plasma-based optical modulation

Hong Ai, Suming Weng, Ping Li, Zhao Liu, Xiaobo Zhang, Zhichao Shen, Xiangbing Wang, Zhaohui Wu, Kaiqiang Pan, Ji Yan, Xiantao Cheng, Zhengming Sheng

2026, 11(4) doi: 10.1063/5.0304306

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Abstract:
High-power, low-coherence laser pulses are essential for suppressing laser–plasma instabilities (LPIs) in inertial confinement fusion (ICF). However, it remains challenging for conventional optical techniques to generate high-power, low-coherence lasers with a fractional bandwidth Δω/ω₀ exceeding 1%. Here, we propose and numerically validate a plasma-based optical modulation scheme for generating high-power, low-coherence laser pulses with an ultrabroad bandwidth of Δω/ω₀ ∼ 5%. This scheme utilizes two laser pulses co-propagating in an underdense plasma: an intense femtosecond driver laser pulse that excites an electron plasma wave, and a subsequent picosecond signal pulse that is spectrally broadened via forward stimulated Raman scattering within the electron plasma wave. More importantly, when the initial signal pulse already possesses a continuous spectrum with a bandwidth Δω larger than the electron plasma frequency ω_pe, the modulated signal pulse exhibits not only a broadened continuous spectrum, but also a significantly shortened coherence time, which is nearly an order of magnitude shorter than that achieved using an initially monochromatic signal pulse. For high-power ICF lasers, the coherence time is a more critical parameter than the bandwidth in evaluating their capability to suppress LPIs. Furthermore, this plasma-based optical modulation scheme achieves a high energy conversion efficiency (η ≳ 99%) and is applicable to frequency-doubled or -tripled laser pulses. Therefore, it offers a promising pathway to the generation of high-power, low-coherence laser pulses for suppressing LPIs in ICF.

Ablation loading efficiency of carbon nanostructured foams produced with the pulsed laser deposition technique

M. Cipriani, A. Maffini, D. Orecchia, M. S. Galli De Magistris, V. Ciardiello, M. Scisciò, P. Andreoli, G. Cristofari, E. Di Ferdinando, V. P. Loschiavo, D. Davino, M. Passoni, F. Consoli

2026, 11(4) doi: 10.1063/5.0316156

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Abstract:
Porous materials have particular advantages for a variety of applications in inertial confinement fusion. To identify suitable new materials for these applications, it is important to investigate their interaction with high-power lasers and the associated plasma evolution. In this work, we report on the results of an experimental campaign performed at the ABC laser facility, employing carefully characterized nanostructured carbon foams obtained with the pulsed laser deposition technique. The enhancement of the ablation loading due to the foam buffer is evaluated by comparing the volume of the crater left after the interaction among different samples. Particular foam parameters and morphology are found to increase the ablation loading by producing a larger crater volume. Visible side-on streak camera images confirm these results. The absorption efficiency is investigated by time-resolved measurement of the laser light collected by focusing lenses and acquired by two fast photodiodes.

Langmuir decay instability for localized Langmuir wave packets in two-dimensional inhomogeneous plasmas

Yongxin Li, Yong Chen, Han Wen, Shang Tan, Yugu Chen, Chengzhuo Xiao

2026, 11(4) doi: 10.1063/5.0314537

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Abstract:
The Langmuir decay instability (LDI) is a key saturation mechanism for stimulated Raman scattering (SRS) in inertial confinement fusion plasmas. However, a quantitative characterization of the two-dimensional angular spectrum of LDI in such inhomogeneous environments, particularly its dependence on the pump-wave incidence angle, remains limited. Here, we combine a k-space theoretical model with two-dimensional particle-in-cell simulations to study a localized Langmuir wave packet in a linear density gradient. Our results show that although the density gradient suppresses the overall strength of LDI, the backscattering channel (φ ≈ 180°) remains the dominant decay mode across all tested pump incidence angles. These results help clarify the multidimensional evolution of LDI in inhomogeneous plasmas and may be useful for developing more predictive models of SRS saturation in laser-fusion schemes.

Phase-field modeling of shock initiation in β-HMX: From hotspot growth to steady detonation

Chengbo Wu, Sui Jia, Yiyuan Jiang, Songlin Yao, Xiaoyang Pei

2026, 11(4) doi: 10.1063/5.0315293

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Abstract:
Understanding how hotspots affect detonation in energetic materials has important scientific and engineering value. The unique material properties of energetic materials impose limitations on research methods, particularly concerning the dynamic characteristics of mesoscale microstructures. In the present work, a coupled crystal plasticity and phase-field model is proposed to address shock initiation in β-HMX explosives. This model employs the phase-field approach to describe hotspot growth processes, enabling entire process simulation from individual hotspot evolution to steady detonation. It quantitatively links collective evolution of multiple hotspots with experimentally measured macroscopic initiation characteristics across stages from slow reaction, through rapid growth, to steady detonation. Phase-field simulations provide a clear physical picture of shock-to-detonation transition (SDT): the growth of individual hotspot leads to the generation of a compression wave that interacts with and catches up to the shock front; numerous compression waves converge at the shock front to form steady detonation waves. Given the strong dependence of explosive SDT on hotspot density and distribution, this method quantifies how individual hotspot growth affects initiation properties. Consequently, it enables evaluation of internal hotspot density and distribution by inversely analyzing macroscopic shock-initiated particle velocity profiles. Furthermore, crystal plasticity simulations allow assessment of how shear strain energy and single-crystal anisotropy influence detonation performance. This work provides a novel means for simulating SDT in energetic explosives, demonstrating substantial engineering application prospects.

Pressure-driven dimensional evolution and two-dimensional superionic state in AlI₃

Yanlei Geng, Junwei Li, Jianfu Li, Yong Liu, Jianan Yuan, Saori Imada Kawaguchi, Qingyang Hu, Xiaoli Wang

2026, 11(4) doi: 10.1063/5.0320987

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Abstract:
Iodide ions can form crystal lattices with large interstitial spaces, making them archetypal systems for investigating superionic phase transitions. Understanding how iodine-based lattices evolve under different thermodynamic conditions is therefore a central problem in condensed matter physics and functional materials design. Aluminum iodide (AlI₃) is a molecular solid crystal with low ionic conductivity under ambient conditions, and it plays important roles in batteries and catalytic applications, motivating exploration of its pressure-tunable ionic transport behavior. Here, we reveal the pressure-induced structural dimensionality evolution in AlI₃ through first-principles structural searches and synchrotron X-ray diffraction (XRD). We identify a sequence of phase transitions: from the molecular P2₁/c phase to a two-dimensional layered rhombohedral (R-3) phase above 1.3 GPa, and subsequently to a one-dimensional chain-like orthorhombic (Cmcm) phase beyond 49 GPa. Notably, in situ laser-heating XRD and ab initio molecular dynamics simulations reveal that the R-3 phase undergoes a transition to a superionic state at high temperatures, where Al³⁺ ions undergo partially disordered, rapid diffusion within the rigid iodine layers. We further demonstrate that the introduction of Al³⁺ vacancies substantially reduces the superionic transition temperature. Our work not only maps the structural evolution of AlI₃ under pressure, but also provides a key reference for the structural design of metal halides under high pressure.

Revisiting the structural and optical properties of γ-N₂

Jinwei Yan, Hai-An Xu, Pu Wang, Lewis J. Conway, Wan Xu, Chuansheng Hu, Zeming Qi, Xiao-Di Liu, Eugene Gregoryanz

2026, 11(4) doi: 10.1063/5.0315313

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Abstract:
For decades, γ-N₂ has been known to exist at very low temperatures and pressures, located in a tiny area of the nitrogen phase diagram. Recently, it was shown that γ-N₂ occupies most of the P–T space usually associated with molecular phases such as δ, ɛ, and ζ, and that it plays a pivotal role in shaping nitrogen’s phase diagram. Using powder synchrotron X-ray diffraction, Raman and infrared spectroscopy, and density function theory calculations, we have investigated the structural and optical properties of γ-N₂ in a wide P–T range. The combined X-ray diffraction and infrared spectroscopy results unequivocally demonstrate that γ-N₂ adopts the monoclinic (P2₁/c space group) configuration with two N₂ molecules per unit cell. It appears that the γ-N₂ is structurally closely related to θ-N₂, leading to both phases having very similar Raman signatures. Additionally, the Raman spectroscopy reveals a vibrational mode intensity resonance effect in both phases, caused by a strong vibrational coupling between the isotopic ¹⁵N¹⁴N and ¹⁴N₂ vibrational excitations.

Current Issue
2026, Volume 11, Issue 4

Current Issue

Current Issue 2026, Volume 11, Issue 4

Current Issue

Current Issue
2026, Volume 11, Issue 4