Showing 1–50 of 91 results for author: Geng, Y

A New Paradigm for 3D Turbomachinery Design: Generative Diffusion Model Based Framework with Direct Geometry Encoding

Authors: Yingfan Geng, Jinhong Wang, Lazaros Papachristodoulou, Sibo Cheng, Teng Cao

Abstract: The aerodynamic design of turbomachinery is critical to the performance of the overall energy system, yet it is challenging due to the complex non-linear flow physics and the presence of multiple-target design compromises. Denoising diffusion model, as one of the leading approaches in generative machine learning, has shown its advantages of high design solution accuracy and diversity in many engin… ▽ More The aerodynamic design of turbomachinery is critical to the performance of the overall energy system, yet it is challenging due to the complex non-linear flow physics and the presence of multiple-target design compromises. Denoising diffusion model, as one of the leading approaches in generative machine learning, has shown its advantages of high design solution accuracy and diversity in many engineering applications. In this study, we bring it to the 3D inverse design problem of turbomachinery, using centrifugal compressors as a classic representative, to demonstrate the new methodology for complex geometry designs. A diffusion model-centred design framework has been developed in this study. By specifying the desired design condition (mass flow rate and rotational speed) and targeted performance (pressure ratio and efficiency), the trained diffusion model returns directly the 3D compressor geometry that satisfies the condition inputs. Compared to traditional deterministic forward design approaches, the proposed method not only generates accurate geometry solutions to inverse design problems, but also enables effective exploration of the entire design space, providing a diverse set of candidate solutions. In addition, this paper presents the first study to directly train on 3D blade geometry coordinates rather than parametrised representations, demonstrating the feasibility of coordinate-based learning while enabling a highly flexible framework applicable to a wide range of designs. The trained diffusion model achieves excellent design capability, with solution accuracy up to 99% and unfeasible designs less than 1%. Furthermore, the solution diversity of the trained diffusion model is also quantitatively verified by means of comparing the distribution of the solution sets generated from the diffusion model and from direct sampling of physical parameters. △ Less

Submitted 29 July, 2026; originally announced July 2026.

Impact of Residual Angular Chirp in a Petawatt-class Laser System on Laser-driven Proton Acceleration

Authors: Qingfan Wu, Minjian Wu, Jiarui Zhao, Ying Gao, Haoran Chen, Tan Song, Zhongshuai Zhang, Zhangyi Wu, Tianhao Liang, Shirui Xu, Ziyang Peng, Hui Zhang, Tianqi Xu, Qihang Han, Chenghao Hua, Ke Chen, Pengcheng Fan, Yuntian Xie, Xianduo Li, Peiqiang Liu, Xiangyu Nong, Shengxuan Xu, Liyong Ma, Yixing Geng, Chen Lin , et al. (3 additional authors not shown)

Abstract: Laser-driven proton acceleration has attracted considerable interest owing to its appealing potential in versatile applications including cancer therapy. Proton energies depend critically on the on-target intensities, yet the detrimental impact of focal spot degradation induced by spatiotemporal couplings on the acceleration remains insufficiently elucidated. In this study, we demonstrate that res… ▽ More Laser-driven proton acceleration has attracted considerable interest owing to its appealing potential in versatile applications including cancer therapy. Proton energies depend critically on the on-target intensities, yet the detrimental impact of focal spot degradation induced by spatiotemporal couplings on the acceleration remains insufficiently elucidated. In this study, we demonstrate that residual angular chirp (AC), stemming from minor misalignments of the grating compressor in a Petawatt-class laser system, acts as a critical bottleneck for proton acceleration. Experimental results reveal that even around 100 microradians of grating misalignment induces substantial focal-spot elongation and a pronounced reduction in peak intensity. By implementing an in situ spectral-blocking diagnostic, we effectively eliminated the residual AC and restored a near-diffraction-limited focus. This optimization led to a significant recovery of the on-target intensity, resulting in a twofold increase in the proton cutoff energy. Our work presents a successful demonstration of diagnosing and eliminating residual AC. This provides a practical reference for generating high-energy proton beams and supporting their diverse applications in a PW-class laser. △ Less

Submitted 14 July, 2026; originally announced July 2026.

Comments: Accepted by Matter and Radiation at Extremes (MRE)

HotLoop Optimization of Petawatt Laser Focal Spot via a Twin-Focus Scheme

Authors: Qingfan Wu, Ying Gao, Minjian Wu, Jiarui Zhao, Shiyou Chen, Tianhao Liang, Haoran Chen, Tan Song, Zhongshuai Zhang, Zhangyi Wu, Shirui Xu, Ziyang Peng, Tianqi Xu, Zhuo Pan, Yujia Zhang, Qihang Han, Ke Chen, Chenghao Hua, Pengcheng Fan, Yuntian Xie, Yifei Shen, Shengxuan Xu, Liyong Ma, Yixing Geng, Chen Lin , et al. (3 additional authors not shown)

Abstract: Achieving diffraction-limited focusing of high-power laser pulses to generate ultra-high intensities is crucial for developing compact laser-driven particle accelerators and exploring strong-field quantum electrodynamics. However, accurately diagnosing and optimizing the focal spots of petawatt (PW) laser pulses remains a significant challenge. In this work, we present an experimental methodology… ▽ More Achieving diffraction-limited focusing of high-power laser pulses to generate ultra-high intensities is crucial for developing compact laser-driven particle accelerators and exploring strong-field quantum electrodynamics. However, accurately diagnosing and optimizing the focal spots of petawatt (PW) laser pulses remains a significant challenge. In this work, we present an experimental methodology utilizing a twin-focus scheme to precisely characterize the intensity distribution and wavefront of focused PW femtosecond laser pulses, and employ it to elucidate their power-dependent evolution. Furthermore, we optimized the focal spots at full power via our in-situ wavefront correction method termed ``HotLoop', achieving a Strehl ratio of 0.80 for 1 PW laser pulses. Consequently, the cutoff proton energies in laser proton acceleration experiments were significantly enhanced. The success of this approach underscores the necessity of in-situ high-energy wavefront correction for ultra-high intensity laser-matter interactions. △ Less

Submitted 19 May, 2026; originally announced May 2026.

Comments: Accepted by Matter and Radiation at Extremes (MRE)

General linear correction method for DFT+X energy: application to U-M (M=Al, Ga, In) alloys under high pressure

Authors: X. L. Pan, H. X. Song, Y. Sun, F. C. Wu, H. Wang, Y. F. Wang, Y. Chen, X. R. Chen, Hua Y. Geng

Abstract: DFT+X methods, such as DFT+U and DFT+DMFT, are important supplements to standard density functional theory when strong on-site Coulomb interactions are present. However, the involvement of external parameters in the underlying model Hamiltonian introduces intrinsic ambiguity when comparing the total energies obtained with different model parameters. This renders DFT+X approaches semi-empirical and… ▽ More DFT+X methods, such as DFT+U and DFT+DMFT, are important supplements to standard density functional theory when strong on-site Coulomb interactions are present. However, the involvement of external parameters in the underlying model Hamiltonian introduces intrinsic ambiguity when comparing the total energies obtained with different model parameters. This renders DFT+X approaches semi-empirical and severely hinders their capability to describe phase ordering and phase stability, especially when reliable experimental benchmarks are unavailable, such as under high pressure. In this work, we resolve this longstanding problem by proposing a general linear correction method that eliminates the ambiguous energy contributions introduced by the model Hamiltonian in DFT+X approaches, thereby enabling direct comparison of their energies calculated with different interaction parameters. The method is demonstrated and validated within the framework of DFT+U, an important member of the DFT+X family. It is then applied to important nuclear materials of uranium-based binaries U-M (M=Al, Ga, In) alloys. With this approach, we resolve the long-standing discrepancy between theoretical predictions and experimental observations of phase stability with unprecedented accuracy, and predict several previously unknown stable intermetallic compounds under high pressure. The broad applicability of the method is further confirmed by accurate predictions of formation enthalpies for diverse systems, including Np-Al, U-Si, and Cu-O binaries, the ternary MnSnAu compound, and oxygen adsorption on the Cu(111) surface. This work establishes linear-corrected DFT+U as a fully first-principles approach and validates the linear correction method as a robust and general scheme that can be readily extended to other DFT+X methods. △ Less

Submitted 28 February, 2026; originally announced March 2026.

Comments: 45 pages, 5 figures, with Supplementary Material

Journal ref: Acta Materialia 306, 121935 (2026)

Effects of realistic laser intensity and phase distribution on high-charge laser wakefield acceleration

Authors: Yuhui Xia, Zhenan Wang, Ziyao Tang, Jianghao Hu, Qianyi Ma, Yuekai Chen, Letian Liu, Zhiyan Yang, Hui Zhang, Chenxu Wang, Haoyang Lan, Di Wu, Xiuhong Yang, Yixing Geng, Yanying Zhao, Xueqin Yan, Xinlu Xu

Abstract: Laser wakefield acceleration (LWFA) can produce relativistic electron beams and various secondary particles in centimeter-long plasmas, making it a valuable particle source with important applications in many disciplines. In this work, we examine the effects of non-ideal transverse intensity and phase distribution of laser pulses on LWFA through both experimental measurements and particle-in-cell… ▽ More Laser wakefield acceleration (LWFA) can produce relativistic electron beams and various secondary particles in centimeter-long plasmas, making it a valuable particle source with important applications in many disciplines. In this work, we examine the effects of non-ideal transverse intensity and phase distribution of laser pulses on LWFA through both experimental measurements and particle-in-cell simulations. The complex transverse profile of the 75 TW laser pulses reduces the self-focused intensity in plasma compared with a transversely Gaussian laser. Furthermore, the sheath structure of the nonlinear plasma wake excited by realistic laser pulses is wider and more complicated than that of a Gaussian laser. These hinder the injection of the plasma electrons. As the laser pulse propagates through the plasma, its intensity profile gradually becomes elliptical and drives a plasma wake with a sharp sheath near the azimuths of the major axis, leading to an injection. When using a realistic laser profile in simulations, both the charge and energy of injected electrons closely match experimental results ($\sim200$ pC of charge and $\sim 200$ MeV peak energy), whereas the Gaussian laser simulations produce much higher charge ($\sim500$ pC). Our findings reveal the difference in injection dynamics between LWFA driven by non-ideal laser pulses and those driven by Gaussian pulses, and are useful for applications of LWFA which demand high-charge electron beams. △ Less

Submitted 25 February, 2026; originally announced February 2026.

Comments: 11 pages, 10 figures

Remote dispersion scan: transformer-network retrieval of ultrafast pulses after non-linear propagation

Authors: Kevin Watson, Yutong Geng, Tobias Saule, Thomas Weinacht, Carlos A. Trallero-Herrero

Abstract: Accurate and rapid characterization of broadband electric fields is essential for all ultrafast applications and remains an active field of research. In this work, we introduce remote dispersion scan, a transformer neural network enabled dispersion scan based pulse characterization method that can characterize femtosecond laser pulses. A local scan of the non-linear spectral phase before several l… ▽ More Accurate and rapid characterization of broadband electric fields is essential for all ultrafast applications and remains an active field of research. In this work, we introduce remote dispersion scan, a transformer neural network enabled dispersion scan based pulse characterization method that can characterize femtosecond laser pulses. A local scan of the non-linear spectral phase before several linear and nonlinear processes, including amplification, compression, and self phase modulation, allows for the field retrieval remotely at the interaction region. We show that the reconstruction accuracy obtained from a single measurement of the fundamental and second harmonic is comparable to that of a full two dimensional scan. We confirm the technique experimentally by compressing a 300 W, 1.3 ps, 1030 nm pulse in a hollow core fiber to 100 fs and measuring the fundamental and second harmonic spectra while scanning the second order phase in a pulse shaper before power amplification. These results establish a simple, robust, alignment insensitive live-view pulse reconstruction modality. △ Less

Submitted 23 January, 2026; originally announced January 2026.

Diffusion Model Driven Airfoil Design: From Geometry Encoding to Practical Applications

Authors: Yingfan Geng, Jinhong Wang, Teng Cao

Abstract: Diffusion model, the state-of-the-art generative machine learning architecture, has shown promising results airfoil inverse designs. In this study, we implemented and trained a series of diffusion models on three different airfoil geometry data encoding formats -- principal component weights, ordered $x$-$y$ coordinates, and 2D signed distance functions (SDF) -- to generate 2D airfoils. By systema… ▽ More Diffusion model, the state-of-the-art generative machine learning architecture, has shown promising results airfoil inverse designs. In this study, we implemented and trained a series of diffusion models on three different airfoil geometry data encoding formats -- principal component weights, ordered $x$-$y$ coordinates, and 2D signed distance functions (SDF) -- to generate 2D airfoils. By systematically comparing the performance of diffusion models trained on different data structures, it is found that for 2D airfoil design problems, the diffusion model performs the best when directly trained with coordinates. Training with latent space (PCA weights in this study) limits the model's design freedom, and decreases the training effectiveness. Although the 2D SDF data appears to result in the least performing model, it proves its feasibility in aerodynamic shape generation, paving the way towards 3D problems where SDF is more favored. This study also investigated deploying the diffusion model in practical engineering applications. A multi-target optimization procedure is proposed based on the stochastic nature of the diffusion process, which drastically simplifies the procedure compared to conventional methods. The extrapolation performance of the model is also investigated by tasking the model with both aerodynamic and flow condition labels that are extrapolated beyond the training set boundaries. △ Less

Submitted 20 January, 2026; originally announced January 2026.

Comments: This draft paper contains 26 pages, 13 figures and 7 tables. Pre-print to be submitted to AIAA journal

Dynamics of Multi-Agent Actor-Critic Learning in Stochastic Games: from Multistability and Chaos to Stable Cooperation

Authors: Yuxin Geng, Wolfram Barfuss, Feng Fu, Xingru Chen

Abstract: Achieving robust coordination and cooperation is a central challenge in multi-agent reinforcement learning (MARL). Uncovering the mechanisms underlying such emergent behaviors calls for a dynamical understanding of learn processes. In this work, we investigate the dynamics of actor-critic agents in stochastic games, focusing on the impact of entropy regularization. By leveraging time-scale separat… ▽ More Achieving robust coordination and cooperation is a central challenge in multi-agent reinforcement learning (MARL). Uncovering the mechanisms underlying such emergent behaviors calls for a dynamical understanding of learn processes. In this work, we investigate the dynamics of actor-critic agents in stochastic games, focusing on the impact of entropy regularization. By leveraging time-scale separation, we derive the system's evolution equations, which are then formally analyzed using dynamical systems theory. We find that in the constant-sum game of Matching Pennies, the system exhibits chaotic behavior. Entropy regularization mitigates this chaos and drives the dynamics toward convergence to fair cooperation. In contrast, in the general-sum game of the Prisoner's Dilemma, the system displays multistability. Interestingly, the three stable equilibria of the system correspond to the well-known ALLC (Always Cooperate), ALLD (Always Defect), and GRIM (Grim Trigger) strategies from evolutionary game theory (EGT). Entropy regularization strengthens system resilience by enlarging the basin of attraction of the cooperative equilibrium. Our findings reveal a close link between the mechanism of direct reciprocity in EGT and how cooperation emerges in MARL, offering insights for designing more robust and collaborative multi-agent systems. △ Less

Submitted 11 January, 2026; originally announced January 2026.

Calibration Method of Spacecraft-Inertial Sensor Center-of-Mass Offset for the Taiji Gravitational Wave Detection Mission under Science Mode

Authors: Haoyue Zhang, Dong Ye, Peng Xu, Yunhai Geng, Li-E Qiang, Ziren Luo

Abstract: Accurately calibrating the center-of-mass (CoM) offset between the spacecraft (SC) and the inertial sensor test mass (TM) is crucial for space-based gravitational-wave (GW) antennas, such as LISA and Taiji. Current calibration methods require additional spacecraft maneuvers that disrupt science data continuity and inter-satellite links, compromising the coherence of gravitational wave signals. Her… ▽ More Accurately calibrating the center-of-mass (CoM) offset between the spacecraft (SC) and the inertial sensor test mass (TM) is crucial for space-based gravitational-wave (GW) antennas, such as LISA and Taiji. Current calibration methods require additional spacecraft maneuvers that disrupt science data continuity and inter-satellite links, compromising the coherence of gravitational wave signals. Here, we present a maneuver-free calibration scheme that directly estimates the CoM offset vector using only standard science-mode measurements from inertial sensors, interferometers, and differential wavefront sensors. By embedding the CoM offset induced coupling acceleration as an extended state in a model-based adaptive Kalman filter, we achieve estimation accuracy of 0.01-1.5 mm across all axes with a maximum error below 1%. This approach enables continuous, high-precision calibration during nominal observation runs, ensuring continuous and coherent gravitational wave data collection while maintaining the required precision, and also facilitating advanced DFACS functions such as performance evaluations and fault diagnosis. For LISA-like missions, where data continuity is paramount for detecting faint gravitational wave signals, this method will enhance scientific output and reliability. △ Less

Submitted 22 January, 2026; v1 submitted 23 December, 2025; originally announced December 2025.

Comments: 15 pages, 12 figures, Calibration study for the Taiji gravitational-wave mission in science mode

Rational regulation strategies of interstitial localized electrons in electride: A density functional theory study

Authors: L. Zhang, D. Wang, H. Wang, J. Li, Y. F. Wang, Q. Wu, Hua Y. Geng

Abstract: As a class of electron-rich materials, electrides demonstrate promising applications in many fields. However, the required high pressure restricts the practical applications to some extent. This study reveals that the unique feature of electride, i.e., the localization of interstitial electrons, can be greatly enhanced and tuned by self-defective doping, applying tensile/compressive stress, or she… ▽ More As a class of electron-rich materials, electrides demonstrate promising applications in many fields. However, the required high pressure restricts the practical applications to some extent. This study reveals that the unique feature of electride, i.e., the localization of interstitial electrons, can be greatly enhanced and tuned by self-defective doping, applying tensile/compressive stress, or shear stress. Moreover, the requirement of orbital orthogonality between the valence and core electron wave functions, as well as the Pauli exclusion principle, should be the driven force for the electron interstitial localization; and the exertion of external pressure modifies the available space to accommodate the electronic wave functions, thus enhances the interstitial localization. These discoveries lay down the ground for searching for promising electrides that are practicable at ambient conditions. △ Less

Submitted 2 December, 2025; originally announced December 2025.

Comments: 33 pages, 7 figures, with supplementary material

Journal ref: Computational Materials Science 258 (2025) 114117

High-pressure melting and elastic behavior of vanadium and niobium based on ab initio and machine learning molecular dynamics

Authors: Hao Wang, Dan Wang, Long Hao, Jun Li, Hua Y. Geng

Abstract: Under high pressure, the group-VB transition metals vanadium (V) and niobium (Nb) exhibit simple crystal structures but complex physical behaviors, such as anomalous compression-induced softening and heating-induced hardening (CISHIH). Meanwhile, the impact of lattice thermal expansion-induced softening at elevated temperatures on HIH is yet to be investigated. Therefore, this study utilized ab in… ▽ More Under high pressure, the group-VB transition metals vanadium (V) and niobium (Nb) exhibit simple crystal structures but complex physical behaviors, such as anomalous compression-induced softening and heating-induced hardening (CISHIH). Meanwhile, the impact of lattice thermal expansion-induced softening at elevated temperatures on HIH is yet to be investigated. Therefore, this study utilized ab initio (AIMD) and machine learning molecular dynamics (MLMD) to investigate the melting and abnormal mechanical softening-hardening behaviors of V and Nb under high pressure. Simulations reveal that the high-temperature Pnma phase of Nb reported in previous experimental studies is highly susceptible to mechanical instability and reverts to the body-centered cubic (BCC) phase. This discovery prompted a revised determination of the high-pressure melting line of Nb. The melting temperature of Nb significantly exceeds the existing theoretical and experimental estimate compared with that of V. AIMD simulations demonstrate that atomic thermal displacements have a greater influence on the HIH of V and Nb than pure electron temperature effects. In addition, the temperature-dependent anomalous elastic properties of V and Nb were investigated within a pressure range of 0-250 GPa using MLMD. The mechanical properties of V and Nb transitioned from HIH to heating-induced softening, elucidating the competition between thermal-expansion-induced softening and HIH. This study advances fundamental understanding of V and Nb physics, providing crucial theoretical foundations for establishing accurate equations of state and constitutive models for these metals. △ Less

Submitted 25 November, 2025; originally announced November 2025.

Comments: 34 pages, 10 figures, with supplementary material

Journal ref: Phys. Rev. B 112, 094108 (2025)

Appraising the absolute limits of nanotubes and nanospheres to preserve high-pressure materials

Authors: Yin L. Xu, Guang F. Yang, Yi Sun, Hong X. Song, Yu S. Huang, Hao Wang, Xiao Z. Yan, Hua Y. Geng

Abstract: Matter under high pressure often exhibits attractive properties, which, unfortunately, are typically irretrievable when released to ambient conditions. Intuitively, nanostructure engineering might provide a promising route to contain high-pressure phase of materials because of the exceptional mechanical strength at nanoscale. However, there is no available theoretical model that can analyze this p… ▽ More Matter under high pressure often exhibits attractive properties, which, unfortunately, are typically irretrievable when released to ambient conditions. Intuitively, nanostructure engineering might provide a promising route to contain high-pressure phase of materials because of the exceptional mechanical strength at nanoscale. However, there is no available theoretical model that can analyze this possibility, not to mention to quantitatively evaluate the pressure-bearing capability of nano-cavities. Here, a physical model is proposed to appraise the absolute theoretical limit of various nanotubes/nanospheres to preserve high-pressure materials to ambient conditions. By incorporating with first-principles calculations, we screen and select four types of representative nanomaterials: graphene, hexagonal boron nitride (h-BN), biphenylene, and γ-graphyne, and perform systematic investigations. The results indicate that nanotube/nanosphere of graphene exhibits the best pressure-bearing capability, followed by h-BN, biphenylene and γ-graphyne. Our model reveals that the structure with the largest average binding energy per bond and the highest density of bonds will have the highest absolute limit to contain pressure materials, while electron/hole doping and interlayer interactions have minor effects. Our finding suggests that one can utilize nanotube/nanosphere with multiple layers to retrieve compressed material with higher pressures. For example, a single layer graphene sphere can retrieve compressed LaH10 with a volume size of 26 nm3 that corresponding to a pressure of 170 GPa and with a near room temperature superconductor transition of Tc=250 K. Similarly, in order to retrieve the metastable atomic hydrogen or molecular metallic hydrogen at about 250 GPa, it requires only three layers of a nanosphere to contain a volume size of 173 nm^3. △ Less

Submitted 21 November, 2025; originally announced November 2025.

Comments: 34 pages, 9 figures, with supplementary material

Journal ref: ACS Appl. Mater. Interfaces 17, 60985-60996 (2025)

Validation of the copper equation of state via shock loading experiments of loosely associated powders

Authors: Yufeng Wang, Long Hao, Lixin Liu, Fengchao Wu, Shijia Ye, Yuanchao Gan, Yi Sun, Hua Y. Geng

Abstract: High-fidelity shock experiments were performed on copper powders with controlled porosity via improved target fabrication and assembly. Optical velocimetry and multi-channel pyrometry were used to obtain Hugoniot data, isentropic release paths, and interface temperature histories. The results validate a modified two-phase equation of state (EOS) for copper based on the framework of Greeff et al. T… ▽ More High-fidelity shock experiments were performed on copper powders with controlled porosity via improved target fabrication and assembly. Optical velocimetry and multi-channel pyrometry were used to obtain Hugoniot data, isentropic release paths, and interface temperature histories. The results validate a modified two-phase equation of state (EOS) for copper based on the framework of Greeff et al. The measured Hugoniot shows good agreement with the present model but exhibits significant softening above ~156 GPa relative to the original Greeff EOS, indicating that reduction in lattice specific heat becomes essential when shock temperatures exceed three times the melting point (T > 3Tm). Unloading behavior matches hydrodynamic simulations incorporating the recalibrated EOS, confirming its accuracy for off-Hugoniot states. Theoretical analysis of temperature release profiles suggests that the thermal conductivity of shocked copper powders may be considerably higher than first-principles predictions. Crucially, despite heterogeneity in shock heating, the macroscopic dynamic response of copper powders with a porosity of ~1.7 is well captured by an average-density EOS model, supporting the use of porous material experiments for EOS validation under extreme conditions. △ Less

Submitted 21 November, 2025; originally announced November 2025.

Comments: 21 pages, 10 figures

Journal ref: J. Appl. Phys. 138, 175902 (2025)

Hyperbolic Dispersion and Low-Frequency Plasmons in Electrides

Authors: Qi-Dong Hao, Hao Wang, Hong-Xing Song, Xiang-Rong Chen, Hua Y. Geng

Abstract: Natural hyperbolic materials have attracted significant interest in the field of photonics due to their unique optical properties. Based on the initial successful explorations on layered crystalline materials, hyperbolic dispersion was associated with extreme structural anisotropy, despite the rarity of natural materials exhibiting this property. Here we show that non cubic electrides are generall… ▽ More Natural hyperbolic materials have attracted significant interest in the field of photonics due to their unique optical properties. Based on the initial successful explorations on layered crystalline materials, hyperbolic dispersion was associated with extreme structural anisotropy, despite the rarity of natural materials exhibiting this property. Here we show that non cubic electrides are generally promising natural hyperbolic materials owing to charge localization in interstitial sites. This includes elemental and binary electrides, as well as some two-dimensional materials that show prominent in-plane hyperbolic dispersion. They exhibit low plasma frequencies and a broad hyperbolic window spanning the infrared to the ultraviolet. In semiconductor electrides, anisotropic interband transitions provide an additional mechanism for hyperbolic behaviour. These findings remove the previously held prerequisite of structural anisotropy for natural hyperbolic materials, and open up new opportunities, which might change the current strategy for searching and design photonic materials. △ Less

Submitted 21 November, 2025; originally announced November 2025.

Comments: 32 pages, 6 figures, with supplementary information

Journal ref: Communications Physics 8, 384 ( 2025)

Acoustic Phonon-Induced Dephasing in Gallium Nitride Defect-Based Quantum Emitters

Authors: Yifei Geng

Abstract: GaN defect based quantum emitters have recently gained attention as promising single photon sources for quantum information applications. However, dephasing processes, manifested as photoluminescence (PL) linewidth broadening, pose a limitation to photon indistinguishability. In this study, we use a custom built confocal scanning microscope to examine the temperature dependent PL spectra of GaN de… ▽ More GaN defect based quantum emitters have recently gained attention as promising single photon sources for quantum information applications. However, dephasing processes, manifested as photoluminescence (PL) linewidth broadening, pose a limitation to photon indistinguishability. In this study, we use a custom built confocal scanning microscope to examine the temperature dependent PL spectra of GaN defect quantum emitters integrated with solid immersion lenses, with the goal of elucidating their dephasing mechanisms. Our experimental findings show that at low temperatures, the PL lineshape exhibits a Gaussian profile with a constant, temperature independent linewidth, consistent with spectral diffusion. As the temperature increases, the PL lineshape evolves into a Lorentzian, and the temperature dependent linewidth deviates from the common T3 law. Considering the Debye temperature of GaN (about 600 K), the experimentally observed temperature dependent linewidth can be modeled by the quadratic Stark effect modulated by acoustic phonons in defect rich crystals. Furthermore, this model exhibits a level of accuracy comparable to that of the defect-E2(low) optical phonon coupling model previously reported in the literature. Our work reveals the mechanism of acoustic phonon induced dephasing in GaN defect emitters and demonstrates that both acoustic and optical phonons can contribute to their dephasing. △ Less

Submitted 15 June, 2025; originally announced June 2025.

Efficient production of sodium Bose-Einstein condensates in a hybrid trap

Authors: Yanda Geng, Shouvik Mukherjee, Swarnav Banik, Monica Gutierrez Galan, Madison J. Anderson, Hector Sosa-Martinez, Stephen P. Eckel, Ian B. Spielman, Gretchen K. Campbell

Abstract: We describe an apparatus that efficiently produces $^{23}$Na Bose-Einstein condensates (BECs) in a hybrid trap that combines a quadrupole magnetic field with a far-detuned optical dipole trap. Using a Bayesian optimization framework, we systematically optimize all BEC production parameters in modest sized batches of highly correlated parameters. Furthermore, we introduce a Lagrange multiplier-base… ▽ More We describe an apparatus that efficiently produces $^{23}$Na Bose-Einstein condensates (BECs) in a hybrid trap that combines a quadrupole magnetic field with a far-detuned optical dipole trap. Using a Bayesian optimization framework, we systematically optimize all BEC production parameters in modest sized batches of highly correlated parameters. Furthermore, we introduce a Lagrange multiplier-based technique to optimize the duration of different evaporation stages constrained to have a fixed total duration; this enables the progressive creation of increasingly rapid experimental sequences that still generate high quality BECs. Taken together, our techniques constitute a general approach for refining and accelerating sequence-based experimental protocols. △ Less

Submitted 26 September, 2025; v1 submitted 27 May, 2025; originally announced May 2025.

Comments: 10 pages, 6 figures

Journal ref: Rev. Sci. Instrum. 96, 093202 (2025)

Temperature-Dependent Emission Polarization in GaN Defect-Based Quantum Emitters

Authors: Yifei Geng

Abstract: GaN defect-based quantum emitters show significant potential for quantum information technologies, yet their intrinsic nature is not fully understood. In this work, we present results on the temperature-dependent emission polarization of GaN defect single-photon emitters integrated with solid immersion lenses. The photoluminescence (PL) remains linearly polarized over the temperature range of 10K… ▽ More GaN defect-based quantum emitters show significant potential for quantum information technologies, yet their intrinsic nature is not fully understood. In this work, we present results on the temperature-dependent emission polarization of GaN defect single-photon emitters integrated with solid immersion lenses. The photoluminescence (PL) remains linearly polarized over the temperature range of 10K to 300K, with a slight rotation in the polarization direction observed at intermediate temperatures. Possible mechanisms underlying this behavior are analyzed, and a roadmap for future research is outlined. △ Less

Submitted 18 May, 2025; v1 submitted 13 April, 2025; originally announced April 2025.

He-Mg compounds and helium-driven nonmetal transition in metallic magnesium

Authors: Y. S. Huang, H. X. Song, Q. D. Hao, X. L. Pan, D. Wang, H. Wang, Y. F. Wang, Y. Sun, Hua Y. Geng

Abstract: The polymorphism and mechanism of helium compounds is crucial for understanding the physical and chemical nature of He-bearing materials under pressures. Here, we predict two new types of He-bearing compounds, MgHe and MgnHe (n = 6, 8, 10, 15, 18), being formed above 750 GPa by unbiased ab initio structure search. An unexpected bandgap is opened up in MgHe at as low as around 200 GPa. This is the… ▽ More The polymorphism and mechanism of helium compounds is crucial for understanding the physical and chemical nature of He-bearing materials under pressures. Here, we predict two new types of He-bearing compounds, MgHe and MgnHe (n = 6, 8, 10, 15, 18), being formed above 750 GPa by unbiased ab initio structure search. An unexpected bandgap is opened up in MgHe at as low as around 200 GPa. This is the first case of noble gas driven metal-nonmetal transition in all elements. The same mechanism is demonstrated also being applicable to other metallic elements, and making beryllium transform into a non-metallic state, a triumph that is impossible otherwise. Furthermore, the stability of the simple cubic phase of Mg (Mg-sc) is greatly enhanced by mixing with He, which lowers the critical pressure of pure Mg-sc from about 1.1 TPa down to 750 GPa to form ordered substitutional alloying phase of MgnHe on a simple cubic lattice of Mg. This is the first report on Mg-based noble gas substitutional alloy, in sharp contrast to the conventional wisdom that He preferring interstitial sites. The observed striking influences of He demonstrate the rich physics and chemistry of He-bearing compounds under ultra-high pressures. △ Less

Submitted 31 March, 2025; originally announced March 2025.

Comments: 22 pages, 5 figures, with supporting materials

Journal ref: Phys. Rev. B 110, 214102 (2024)

Predicting performance-related properties of refrigerant based on tailored small-molecule functional group contribution

Authors: Peilin Cao, Ying Geng, Nan Feng, Xiang Zhang, Zhiwen Qi, Zhen Song, Rafiqul Gani

Abstract: As current group contribution (GC) methods are mostly proposed for a wide size-range of molecules, applying them to property prediction of small refrigerant molecules could lead to unacceptable errors. In this sense, for the design of novel refrigerants and refrigeration systems, tailoring GC-based models specifically fitted to refrigerant molecules is of great interest. In this work, databases of… ▽ More As current group contribution (GC) methods are mostly proposed for a wide size-range of molecules, applying them to property prediction of small refrigerant molecules could lead to unacceptable errors. In this sense, for the design of novel refrigerants and refrigeration systems, tailoring GC-based models specifically fitted to refrigerant molecules is of great interest. In this work, databases of potential refrigerant molecules are first collected, focusing on five key properties related to the operational efficiency of refrigeration systems, namely normal boiling point, critical temperature, critical pressure, enthalpy of vaporization, and acentric factor. Based on tailored small-molecule groups, the GC method is combined with machine learning (ML) to model these performance-related properties. Following the development of GC-ML models, their performance is analyzed to highlight the potential group-to-property contributions. Additionally, the refrigerant property databases are extended internally and externally, based on which examples are presented to highlight the significance of the developed models. △ Less

Submitted 22 March, 2025; originally announced March 2025.

Pressure induced Structure Change and Anomalies in Thermodynamic Quantities and Transport Properties in Liquid Lithium Hydride

Authors: X. Z. Yan, Y. M. Chen, Hua Y. Geng, Y. F. Wang, Y. Sun, L. L. Zhang, H. Wang, Y. L. Xu

Abstract: Understand the nature of liquid structure and its evolution under different conditions is a major challenge in condensed physics and materials science. Here, we report a pressure-induced structure change spanning a wide pressure range in liquid-state lithium hydride (LiH) by first-principles molecular dynamic simulations. This behavior can be described as a continuous crossover from low pressure l… ▽ More Understand the nature of liquid structure and its evolution under different conditions is a major challenge in condensed physics and materials science. Here, we report a pressure-induced structure change spanning a wide pressure range in liquid-state lithium hydride (LiH) by first-principles molecular dynamic simulations. This behavior can be described as a continuous crossover from low pressure liquid with Li$^+$-H$^-$ duality symmetry to high pressure one with broken of duality symmetry. The thermodynamic quantities such as heat capacity and ionic transport properties such as diffusivity are also saliently impacted. It is important to stress that such behavior is firstly predicted for this category of materials, which is ubiquitous in universe as well as in industry applications. Lastly, a comprehensive high-pressure high-temperature phase diagram of LiH is constructed, which embodies rich physics in this previously-thought-simple ionic compound. △ Less

Submitted 26 January, 2025; originally announced January 2025.

Comments: 23 pages, 4 figures, with Supplementary Information

Journal ref: Phys. Rev. B 111, 024102 (2025)

Simultaneous Superconducting and Topological Properties in Mg-Li Electrides at High Pressures

Authors: D. Wang, H. Song, Q. Hao, G. Yang, H. Wang, L. Zhang, Y. Chen, X. Chen, Hua Y. Geng

Abstract: Electrides as a unique class of emerging materials exhibit fascinating properties and hold important significance for understanding the matter under extreme conditions, which is characterized by valence electrons localized into the interstitial space as quasi-atoms (ISQs). In this work, using crystal structure prediction and first-principles calculations, we identified seven stable phases of Mg-Li… ▽ More Electrides as a unique class of emerging materials exhibit fascinating properties and hold important significance for understanding the matter under extreme conditions, which is characterized by valence electrons localized into the interstitial space as quasi-atoms (ISQs). In this work, using crystal structure prediction and first-principles calculations, we identified seven stable phases of Mg-Li that are electride with novel electronic properties under high pressure. Among them, MgLi10 is a semiconductor with a band gap of 0.22 eV; and Pm-3m MgLi is superconductor with a superconducting transition temperature of 22.8 K. The important role played by the localization degree of ISQ in the superconducting transition temperature of these electrides is revealed by systematic comparison of Mg-Li with other Li-rich electride superconductors. Furthermore, we proved that Pm-3m MgLi and Pnma MgLi also have distinct topological behavior with metallic surface states and the non-zero $Z_2$ invariant. The simultaneous coexistence of superconductivity, electronic band topology and electride property in the same structure of Pm-3m MgLi and Pnma MgLi demonstrates the feasibility of realizing multi-quantum phases in a single material, which will stimulate further research in these interdisciplinary fields. △ Less

Submitted 26 January, 2025; originally announced January 2025.

Comments: 38 pages, 7 figures, with Supporting Information

Journal ref: J. Phys. Chem. C 129, 689-698 (2025)

The Rayleigh-Taylor instability in a binary quantum fluid

Authors: Yanda Geng, Junheng Tao, Mingshu Zhao, Shouvik Mukherjee, Stephen Eckel, Gretchen K. Campbell, Ian B. Spielman

Abstract: Instabilities, where small fluctuations seed the formation of large-scale structures, govern dynamics in a variety of fluid systems. The Rayleigh-Taylor instability (RTI), present from tabletop to astronomical scales, is an iconic example characterized by mushroom-shaped incursions appearing when immiscible fluids are forced together. Despite its ubiquity, RTI experiments are challenging; here, we… ▽ More Instabilities, where small fluctuations seed the formation of large-scale structures, govern dynamics in a variety of fluid systems. The Rayleigh-Taylor instability (RTI), present from tabletop to astronomical scales, is an iconic example characterized by mushroom-shaped incursions appearing when immiscible fluids are forced together. Despite its ubiquity, RTI experiments are challenging; here, we report the observation of the RTI in an immiscible binary superfluid consisting of a two-component Bose-Einstein condensate. We force these components together to initiate the instability, and observe the growth of mushroom-like structures. The interface can also be stabilized, allowing us to spectroscopically measure the "ripplon" interface modes. Lastly, we use matter-wave interferometry to transform the superfluid velocity field at the interface into a vortex chain. These results-in agreement with our theory-demonstrate the close connection between the RTI in classical and quantum fluids. △ Less

Submitted 3 September, 2025; v1 submitted 29 November, 2024; originally announced November 2024.

Comments: 10 pages (including SM), 4 figures + 3 figures in SM

Journal ref: Sci. Adv. 11, eadw9752 (2025)

Distinctive Electronic Characteristics and Ultra-high Thermoelectric Power Factor in Be-Fe Intermetallics

Authors: Q. D. Hao, H. Wang, X. R. Chen, Hua Y. Geng

Abstract: Beryllium (Be) alloys are indispensable in cutting-edge applications due to their unique advantages. However, the scientific understanding about their structure and property is deficient, which greatly restricts their applications within a narrow field. In this work, a systematic investigation on the structure and properties of Be-Fe binary was carried out with first-principles unbiased evolutiona… ▽ More Beryllium (Be) alloys are indispensable in cutting-edge applications due to their unique advantages. However, the scientific understanding about their structure and property is deficient, which greatly restricts their applications within a narrow field. In this work, a systematic investigation on the structure and properties of Be-Fe binary was carried out with first-principles unbiased evolutionary algorithms. Five new intermetallics unreported before, including insulating Be11Fe and Be4Fe, metallic Be3Fe, and metastable BeFe and BeFe2 were discovered, among which Be11Fe has a unique clathrate structure and is an electride. Surprisingly, we found that Fe unexpectedly acts as an anion in all known Be-Fe intermetallics, and its valence state can even reach -5, leading to the complete filling of its 3d orbitals. Most of these compounds exhibiting a gap or pseudogap at the Fermi level. Specifically, the band gap is determined as 0.22 eV and 0.85 eV for Be11Fe and Be4Fe at the level of single-shot GW, respectively. This is the first report of insulating phases in Be-based intermetallics. We also discovered that Be11Fe exhibits an impressive thermoelectric power factor of 178 $μW cm^{-1}K^2$ at room temperature, to our best knowledge, the highest among known semiconductors under ambient conditions, indicating its potential for waste heat harvesting and active cooling. These findings will deepen our understanding of Be-based and Fe-based compounds, and expand the application fields of Be-based alloys to a brand-new realm. △ Less

Submitted 24 November, 2024; originally announced November 2024.

Comments: 29 pages, 6 figures, with Supplementary Information

Journal ref: J. Mater. Chem. A, 12, 24370-24379 (2024)

Theoretical Study on the Structural and Thermodynamic Properties of U-He compounds under High Pressure

Authors: Ye Cao, Hongxing Song, Xiaozhen Yan, Hao Wang, Yufeng Wang, Fengchao Wu, Leilei Zhang, Qiang Wu, Hua Y. Geng

Abstract: Uranium is considered as a very important nuclear energy material because of the huge amount of energy released. As the main products of spontaneous decay of uranium, helium is difficult to react with uranium for its chemical inertness. Therefore, bubbles will be formed inside uranium, which could greatly reduce the performance of uranium or cause the safety problems. Additionally, nuclear materia… ▽ More Uranium is considered as a very important nuclear energy material because of the huge amount of energy released. As the main products of spontaneous decay of uranium, helium is difficult to react with uranium for its chemical inertness. Therefore, bubbles will be formed inside uranium, which could greatly reduce the performance of uranium or cause the safety problems. Additionally, nuclear materials are usually operated in an environment of high-temperature and high-pressure, so it is necessary to figure out the exact state of helium inside uranium at extreme conditions. Here, we explored the structural stability of U-He system under high-pressure and high-temperature by using density functional theory calculations. Two metastable phases are found between 50 and 400 GPa: U4He with space group Fmmm and U6He with space group P-1. Both are metallic and adopt layered structures. Electron localization function calculation combined with charge density difference analysis indicate that there are covalent bonds between U and U atoms in both Fmmm-U4He and P-1-U6He. Compared with the elastic modulus of $α$-U, the addition of helium has certain influence on the mechanical properties of uranium. Besides, first-principles molecular dynamics simulations were carried out to study the dynamical behavior of Fmmm-U4He and P-1-U6He at high-temperature. It is found that Fmmm-U4He and P-1-U6He undergo one-dimensional superionic phase transitions at 150 GPa. Our study revealed exotic structure of U-He compounds beyond the form of bubble under high-pressure and high-temperature, that might be relevant to the performance and safety issue of nuclear materials at extreme conditions. △ Less

Submitted 21 July, 2024; originally announced July 2024.

Comments: 8 pages, 4 figures, with Supplementary Information

Journal ref: Phys. Chem. Chem. Phys. 26, 19228-19235 (2024)

First-principles study of structural and electronic properties of multiferroic oxide Mn3TeO6 under high pressure

Authors: Xiao-Long Pan, Hao Wang, Lei Liu, Xiang-Rong Chen, Hua Y. Geng

Abstract: Mn3TeO6 (MTO) has been experimentally found to adopt a P21/n structure under high pressure, which exhibits a significantly smaller band gap compared to the atmospheric R-3 phase. In this study, we systematically investigate the magnetism, structural phase transition and electronic properties of MTO under high pressure through first-principles calculations. Both R-3 and P21/n phases of MTO are anti… ▽ More Mn3TeO6 (MTO) has been experimentally found to adopt a P21/n structure under high pressure, which exhibits a significantly smaller band gap compared to the atmospheric R-3 phase. In this study, we systematically investigate the magnetism, structural phase transition and electronic properties of MTO under high pressure through first-principles calculations. Both R-3 and P21/n phases of MTO are antiferromagnetic at zero temperature. The R-3 phase transforms to the P21/n phase at 7.58 GPa, accompanied by a considerable volume collapse of about 6.47%. Employing the accurate method that combines DFT+U and G0W0, the calculated band gap of R-3 phase at zero pressure is very close to the experimental values, while that of the P21/n phase is significantly overestimated. The main reason for this difference is that the experimental study incorrectly used the Kubelka-Munk plot for the indirect band gap to obtain the band gap of the P21/n phase instead of the Kubelka-Munk plot for the direct band gap. Furthermore, our study reveals that the transition from the R-3 phase to the P21/n phase is accompanied by a slight reduction in the band gap. △ Less

Submitted 21 July, 2024; originally announced July 2024.

Comments: 17 pages, 11 figures

Journal ref: Chin. Phys. B 33, 076102 (2024)

Fast and accurate extraction of ultra-high quality factor from cavity ring-down measurement

Authors: Yanping Yang, Shihan Liu, Yong Geng, Huashun Wen, Heng Zhou

Abstract: Cavity ring-down is an essential test to measure ultra-high quality factor (UHQ) optical cavities, which is, however, frequently misinterpreted due to lacking of a specified analysis guideline. Here we clarify the basic property of cavity ring down and present a step-by-step method that enables extraction of the overall quality factor, as well as the intrinsic loss and coupling state of UHQ caviti… ▽ More Cavity ring-down is an essential test to measure ultra-high quality factor (UHQ) optical cavities, which is, however, frequently misinterpreted due to lacking of a specified analysis guideline. Here we clarify the basic property of cavity ring down and present a step-by-step method that enables extraction of the overall quality factor, as well as the intrinsic loss and coupling state of UHQ cavities with better fidelity and simplicity than prior schemes. Our work can facilitate acurrate design and characterization of UHQ cavities for ultra-low noise lasers, high finesse reference cavities, and ultra-narrow optical filters. △ Less

Submitted 21 May, 2024; originally announced June 2024.

Unbending strategies shepherd cooperation and suppress extortion in spatial populations

Authors: Zijie Chen, Yuxin Geng, Xingru Chen, Feng Fu

Abstract: Evolutionary game dynamics on networks typically consider the competition among simple strategies such as cooperation and defection in the Prisoner's Dilemma and summarize the effect of population structure as network reciprocity. However, it remains largely unknown regarding the evolutionary dynamics involving multiple powerful strategies typically considered in repeated games, such as the zero-d… ▽ More Evolutionary game dynamics on networks typically consider the competition among simple strategies such as cooperation and defection in the Prisoner's Dilemma and summarize the effect of population structure as network reciprocity. However, it remains largely unknown regarding the evolutionary dynamics involving multiple powerful strategies typically considered in repeated games, such as the zero-determinant (ZD) strategies that are able to enforce a linear payoff relationship between them and their co-players. Here, we consider the evolutionary dynamics of always cooperate (AllC), extortionate ZD (extortioners), and unbending players in lattice populations based on the commonly used death-birth updating. Out of the class of unbending strategies, we consider a particular candidate, PSO Gambler, a machine-learning-optimized memory-one strategy, which can foster reciprocal cooperation and fairness among extortionate players. We derive analytical results under weak selection and rare mutations, including pairwise fixation probabilities and long-term frequencies of strategies. In the absence of the third unbending type, extortioners can achieve a half-half split in equilibrium with unconditional cooperators for sufficiently large extortion factors. However, the presence of unbending players fundamentally changes the dynamics and tilts the system to favor unbending cooperation. Most surprisingly, extortioners cannot dominate at all regardless of how large their extortion factor is, and the long-term frequency of unbending players is maintained almost as a constant. Our analytical method is applicable to studying the evolutionary dynamics of multiple strategies in structured populations. Our work provides insights into the interplay between network reciprocity and direct reciprocity, revealing the role of unbending strategies in enforcing fairness and suppressing extortion. △ Less

Submitted 29 May, 2024; originally announced May 2024.

Comments: 21 pages, 6 figures

A compact and open-source microcontroller-based rapid auto-alignment system

Authors: Yanda Geng, Alan Tsidilkovski, Kevin Weber, Shouvik Mukherjee, Alessandro Restelli, Sarthak Subhankar

Abstract: Maintaining stable and precise alignment of a laser beam is crucial in many optical setups. In this work, we present a microcontroller-based rapid auto-alignment system that detects and corrects for drifts in a laser beam trajectory using a pair of two-dimensional duo-lateral position sensing detectors (PSDs) and a pair of mirror mounts with piezoelectric actuators. We develop hardware and softwar… ▽ More Maintaining stable and precise alignment of a laser beam is crucial in many optical setups. In this work, we present a microcontroller-based rapid auto-alignment system that detects and corrects for drifts in a laser beam trajectory using a pair of two-dimensional duo-lateral position sensing detectors (PSDs) and a pair of mirror mounts with piezoelectric actuators. We develop hardware and software for interfacing with the PSDs and for controlling the motion of the piezoelectric mirrors mounts. Our auto-alignment strategy -- implemented as a state machine on the microcontroller by a FreeRTOS kernel -- is based on a simple linearized geometrical optical model. We benchmark our system using the standard case of coupling laser light efficiently into the guided mode of a single-mode fiber optic patch cable. We can recover the maximum fiber coupling efficiency in $\sim10$ seconds, even for a laser beam that was misaligned to the point of zero fiber coupling. △ Less

Submitted 22 March, 2024; originally announced May 2024.

Comments: 6 pages, 5 figures

Journal ref: Rev. Sci. Instrum. 95, 095003 (2024)

Real-Time Recognition of Vortex Beams Modes Through Random Diffusive at the Speed of Light

Authors: Tong Fu, Gang Luo, Jia Cheng Li, Yuan Chao Geng, Xiao Dong Yuan

Abstract: Optical vortex beam with orbital angular momentum (OAM) has great potential to increase the capacity of optical communication and information processing in classical and quantum regimes. Nevertheless, important challenges that influence the optical data transmission in free space is the existence of diffusers along the optical path, which causes inevitable information loss during the wave propagat… ▽ More Optical vortex beam with orbital angular momentum (OAM) has great potential to increase the capacity of optical communication and information processing in classical and quantum regimes. Nevertheless, important challenges that influence the optical data transmission in free space is the existence of diffusers along the optical path, which causes inevitable information loss during the wave propagation. Numerous algorithms have been proposed successively for identifying the modes of vortex beams propagating through scattering media. However, these methods all require completion on a computer, which is energyintensive and energy consuming. Here, we propose an all-optical regime for identifying the modes of vortex light fields propagating through scattering media. After training by deep learning, our model can recognize the mode of vortex beam through unknown phase diffusers, demonstrating generalization to new random diffusers that have never been encountered before. Once physically deployed, the entire setup will rapidly identify the modes of vortex light propagating through scattering media at the speed of light, and the entire inference process will consume zero energy except for illumination source. Our research represents a significant step towards highly accurate recognition of vortex light modes propagating through complex scattering media, providing significant guidance for the application of optical communication in complex environments. △ Less

Submitted 25 March, 2024; originally announced March 2024.

Modified Steinberg-Guinan elasticity model to describe softening-hardening dual anomaly in vanadium

Authors: Hao Wang, Yuan-Chao Gan, Xiang-Rong Chen, Yi-Xian Wang, Hua Y. Geng

Abstract: Constitutive models are essential for describing the mechanical behavior of materials under high temperatures and pressures, among which the Steinberg-Guinan (SG) model is widely adopted. Recent work has discovered a peculiar dual anomaly of compression-induced softening and heating-induced hardening in the elasticity of compressed vanadium [Phys. Rev. B 104, 134102 (2021)], which is beyond the ca… ▽ More Constitutive models are essential for describing the mechanical behavior of materials under high temperatures and pressures, among which the Steinberg-Guinan (SG) model is widely adopted. Recent work has discovered a peculiar dual anomaly of compression-induced softening and heating-induced hardening in the elasticity of compressed vanadium [Phys. Rev. B 104, 134102 (2021)], which is beyond the capability of the SG model to describe. In this work, a modified SG constitutive model is proposed to embody such an anomalous behavior. Elemental vanadium is considered as an example to demonstrate the effectiveness of this improved model in describing the dual anomalies of mechanical elasticity. This new variant of the SG model can also be applied to other materials that present an irregular variation in the mechanical elasticity, and is important to faithfully model and simulate the mechanical response of materials under extreme conditions. △ Less

Submitted 17 March, 2024; originally announced March 2024.

Comments: 14 pages, 4 figures

Journal ref: J. Appl. Phys. 135, 115901 (2024)

Topological and superconducting properties of two-dimensional C6-2x(BN)x biphenylene network: a first-principles investigation

Authors: Guang F. Yang, Hong X. Song, Dan Wang, Hao Wang, Hua Y. Geng

Abstract: First-principles calculations have been used to investigate the electronic and topological properties of the two-dimensional C6-2x(BN)x biphenylene network, a graphene-like structure composed of not only hexagonal ring but also octagonal and square rings. Nontrivial topological properties have been found in two of them, with a stoichiometry of C4BN and C2(BN)2. The former C4BN is predicted to be a… ▽ More First-principles calculations have been used to investigate the electronic and topological properties of the two-dimensional C6-2x(BN)x biphenylene network, a graphene-like structure composed of not only hexagonal ring but also octagonal and square rings. Nontrivial topological properties have been found in two of them, with a stoichiometry of C4BN and C2(BN)2. The former C4BN is predicted to be a type-II Dirac semimetal with a superconducting critical temperature Tc=0.38K, which is similar to the pure carbon biphenylene network (C-BPN). The latter shows a novel isolated edge state exists between the conduction and valence bands. By regulation of strains and virtual-crystal approximation calculations, we found the annihilation of two pairs of Dirac points (DPs) in the non-high symmetric region (non-HSR) causes the two corresponding edge states stick together to generate this isolated edge state. In addition, we found that one pair of DPs arises from the shift of DPs in the C-BPN, while another new pair of DPs emerges around the Time Reversal Invariant Momenta (TRIM) point X due to the doping of boron and nitrogen. We constructed a tight-binding (TB) model to reveal the mechanism of forming the isolated edge state from the C-BPN to C2(BN)2. This study not only demonstrates the existence and mechanism of forming the isolated edge state in semimetals, but also provides an example in which the DPs can move away from the high-symmetry region. △ Less

Submitted 24 February, 2024; originally announced February 2024.

Comments: 32 pages, 10 figures, with supplementary materials

Journal ref: Phys. Rev. B 109, 125424 (2024)

Universal Metallic Surface States in Electride

Authors: Dan Wang, Hongxing Song, Leilei Zhang, Hao Wang, Yi Sun, Fengchao Wu, Ying Chen, Xiangrong Chen, Hua Y. Geng

Abstract: Robust metallic surface states (MSS) of topological insulator (TI) against imperfections and perturbations are important in broad applications such as chemical catalysis and quantum computing. Unfortunately, they are suffered from the narrow band gap that can be accessed. Searching for MSS with large bulk band gap beyond conventional TIs becomes a quest. In this work, inspired by the adiabatic con… ▽ More Robust metallic surface states (MSS) of topological insulator (TI) against imperfections and perturbations are important in broad applications such as chemical catalysis and quantum computing. Unfortunately, they are suffered from the narrow band gap that can be accessed. Searching for MSS with large bulk band gap beyond conventional TIs becomes a quest. In this work, inspired by the adiabatic connection principle in real space, we identify that all electrides, a new class of emerging materials, must host robust and universal MSS that resists any disturbances, in spite of the fact that some of them could be classified as trivial in standard topology theory. This counterintuitive property is traced to the specific charge localization-delocalization change intrinsic to electride when approaching the crystalline surface or interface, which is a kind of interstice-centered to atom-centered transition in the real-space topology of the charge density distribution, and is sharply different from the band inversion in the standard topology theory. The new mechanism circumvents the obstacle that limits the band gap of TI. Robust and universal MSS in an electride that conventionally-determined as trivial but with a colossal band gap beyond 6.13 eV are demonstrated. This gap size is about 6-fold larger than the highest record of known "wide-gap" TIs, thus opens up new avenues to universal MSS with gigantic bulk gap. △ Less

Submitted 24 February, 2024; originally announced February 2024.

Comments: 32 pages, 7 figures, with supporting information

Journal ref: J. Phys. Chem. C 2024, 128, 1845-1854

Prediction of novel ordered phases in U-X (X= Zr, Sc, Ti, V, Cr, Y, Nb, Mo, Hf, Ta, W) binary alloys under high pressure

Authors: Xiao L. Pan, Hong X. Song, H. Wang, F. C. Wu, Y. C. Gan, Xiang R. Chen, Ying Chen, Hua Y. Geng

Abstract: U-based binary alloys have been widely adopted in fast nuclear reactors, but their stability under extreme conditions of high-pressure is almost unknown, mounting up to latent risk in applications. Here, possible ordered phases in U-Zr system up to 200 GPa are comprehensively investigated by unbiased first-principles structure prediction. Stable U2Zr, metastable U3Zr and U4Zr phases are discovered… ▽ More U-based binary alloys have been widely adopted in fast nuclear reactors, but their stability under extreme conditions of high-pressure is almost unknown, mounting up to latent risk in applications. Here, possible ordered phases in U-Zr system up to 200 GPa are comprehensively investigated by unbiased first-principles structure prediction. Stable U2Zr, metastable U3Zr and U4Zr phases are discovered for the first time, which exhibit strong stability under compression. They all are metallic, with 5f electrons of uranium dominating the electronic density of states near the Fermi level. Prominent ionic interactions between U and Zr atoms, as well as covalent interactions between adjacent uranium atoms, are found. The same strategy is applied to explore the stability of ordered phases in other U-based binary transition metal alloys, U-X (X= Sc, Ti, V, Cr, Y, Nb, Mo, Hf, Ta, W). Stable and metastable ordered phases similar to U-Zr alloy are unveiled, all with similar electronic structures. For these alloys, we find that the structure of U2X (X=Zr, Ti, Hf) hosts a unique hybrid phase transition similar to U2Nb, which is a superposition of a first-order transition and a second-order transition. The prediction of these novel phases not only refutes the stability of the long-believed ordered phase I4/mmm-U2Mo, but also rewrites the phase diagrams of U-X (X= Zr, Sc, Ti, V, Cr, Nb, Mo, Hf, Ta) alloys under high pressure. All of these findings promote our understanding of the high-pressure behavior of the broad category of U-based binary alloys with transition metals. △ Less

Submitted 24 February, 2024; originally announced February 2024.

Comments: 27 pages, 12 figures, with supplementary material

Journal ref: Acta Materialia 263, 119489 (2024)

Prediction of Superionic State in LiH2 at Conditions Enroute to Nuclear Fusion

Authors: Fude Li, Hao Wang, Jinlong Li, Hua Y. Geng

Abstract: Hydrogen and lithium, along with their compounds, are crucial materials for nuclear fusion research. High-pressure studies have revealed intricate structural transitions in all these materials. However, research on lithium hydrides beyond LiH has mostly focused on the low-temperature regime. Here, we use density functional theory and ab initio molecular dynamics simulations to investigate the beha… ▽ More Hydrogen and lithium, along with their compounds, are crucial materials for nuclear fusion research. High-pressure studies have revealed intricate structural transitions in all these materials. However, research on lithium hydrides beyond LiH has mostly focused on the low-temperature regime. Here, we use density functional theory and ab initio molecular dynamics simulations to investigate the behavior of LiH2, a hydrogen-rich compound, near its melting point. Our study is particularly relevant to the low-pressure region of the compression pathway of lithium hydrides toward fusion. We discovered a premelting superionic phase transition in LiH2 that has significant implications for its mass transportation, elastic properties, and sound velocity. The theoretical boundary for the superionic transition and melting temperature was then determined. In contrast, we also found that the primary compound of lithium hydrides, LiH, does not exhibit a superionic transition. These findings have important implications for optimizing the compression path to achieve the ignition condition in inertial confinement fusion research, especially when lithium tritium-deuteride(LiTD) are used as the fuel. △ Less

Submitted 24 February, 2024; originally announced February 2024.

Comments: 17 pages, 7 figures, with supplementary material

Journal ref: Chinese Physics B 32, 106103 (2023)

Ultra-short lifetime isomer studies from photonuclear reactions using laser-driven ultra-intense γ-ray

Authors: Di Wu, Haoyang Lan, Jiaxing Liu, Huangang Lu, Jianyao Zhang, Jianfeng Lv, Xuezhi Wu, Hui Zhang, Yadong Xia, Qiangyou He, Jie Cai, Qianyi Ma, Yuhui Xia, Zhenan Wang, Meizhi Wang, Zhiyan Yang, Xinlu Xu, Yixing Geng, Chen Lin, Wenjun Ma, Yanying Zhao, Haoran Wang, Fulong Liu, Chuangye He, Jinqing Yu , et al. (7 additional authors not shown)

Abstract: Isomers, ubiquitous populations of relatively long-lived nuclear excited states, play a crucial role in nuclear physics. However, isomers with half-life times of several seconds or less barely had experimental cross section data due to the lack of a suitable measuring method. We report a method of online γ spectroscopy for ultra-short-lived isomers from photonuclear reactions using laser-driven ul… ▽ More Isomers, ubiquitous populations of relatively long-lived nuclear excited states, play a crucial role in nuclear physics. However, isomers with half-life times of several seconds or less barely had experimental cross section data due to the lack of a suitable measuring method. We report a method of online γ spectroscopy for ultra-short-lived isomers from photonuclear reactions using laser-driven ultra-intense γ-rays. The fastest time resolution can reach sub-ps level with γ-ray intensities >10^{19}/s ({\geqslant} 8 MeV). The ^{115}In(γ, n)^{114m2}In reaction (T_{1/2} = 43.1 ms) was first measured in the high-energy region which shed light on the nuclear structure studies of In element. Simulations showed it would be an efficient way to study ^{229m}Th (T_{1/2} = 7 μs), which is believed to be the next generation of nuclear clock. This work offered a unique way of gaining insight into ultra-short lifetimes and promised an effective way to fill the gap in relevant experimental data. △ Less

Submitted 23 February, 2024; originally announced February 2024.

Evolutionary Dynamics with Randomly Distributed Benevolent Individuals

Authors: Yuxin Geng, Xingru Chen

Abstract: Understanding the evolution of cooperation is pivotal in biology and social science. Public resources sharing is a common scenario in the real world. In our study, we explore the evolutionary dynamics of cooperation on a regular graph with degree $k$, introducing the presence of a third strategy, namely the benevolence, who does not evolve over time, but provides a fixed benefit to all its neighbo… ▽ More Understanding the evolution of cooperation is pivotal in biology and social science. Public resources sharing is a common scenario in the real world. In our study, we explore the evolutionary dynamics of cooperation on a regular graph with degree $k$, introducing the presence of a third strategy, namely the benevolence, who does not evolve over time, but provides a fixed benefit to all its neighbors. We find that the presence of the benevolence can foster the development of cooperative behavior and it follows a simple rule: $b/c > k - p_S(k-1)$. Our results provide new insights into the evolution of cooperation in structured populations. △ Less

Submitted 30 December, 2023; originally announced January 2024.

Extremely powerful and frequency-tunable terahertz pulses from a table-top laser-plasma wiggler

Authors: Jie Cai, Yinren Shou, Yixing Geng, Liqi Han, Xinlu Xu, Shuangchung Wen, Baifei Shen, Jinqing Yu, Xueqing Yan

Abstract: The production of broadband, terawatt terahertz (THz) pulses has been demonstrated by irradiating relativistic lasers on solid targets. However, the generation of extremely powerful, narrow-band, and frequency-tunable THz pulses remains a challenge. Here, we present a novel approach for such THz pulses, in which a plasma wiggler is elaborated by a table-top laser and a near-critical density plasma… ▽ More The production of broadband, terawatt terahertz (THz) pulses has been demonstrated by irradiating relativistic lasers on solid targets. However, the generation of extremely powerful, narrow-band, and frequency-tunable THz pulses remains a challenge. Here, we present a novel approach for such THz pulses, in which a plasma wiggler is elaborated by a table-top laser and a near-critical density plasma. In such a wiggler, the laser-accelerated electrons emit THz radiations with a period closely related to the plasma thickness. Theoretical model and numerical simulations predict a THz pulse with a laser-THz energy conversion over 2.0$\%$, an ultra-strong field exceeding 80 GV/m, a divergence angle approximately 20$^\circ$, and a center-frequency tunable from 4.4 to 1.5 THz, can be generated from a laser of 430 mJ. Furthermore, we demonstrate that this method can work across a wide range of laser and plasma parameters, offering potential for future applications with extremely powerful THz pulse. △ Less

Submitted 25 August, 2023; originally announced August 2023.

Violation of the Wiedemann-Franz law in coupled thermal and power transport of optical waveguide arrays

Authors: Meng Lian, Yin-Jie Chen, Yue Geng, Yun-Tian Chen, Jing-Tao Lü

Abstract: In isolated nonlinear optical waveguide arrays with bounded energy spectrum, simultaneous conservation of energy and power of the optical modes enables study of coupled thermal and particle transport in the negative temperature regime. Here, based on exact numerical simulation and rationale from Landauer formalism, we predict generic violation of the Wiedemann-Franz law in such systems. This is ro… ▽ More In isolated nonlinear optical waveguide arrays with bounded energy spectrum, simultaneous conservation of energy and power of the optical modes enables study of coupled thermal and particle transport in the negative temperature regime. Here, based on exact numerical simulation and rationale from Landauer formalism, we predict generic violation of the Wiedemann-Franz law in such systems. This is rooted in the spectral decoupling of thermal and power current of optical modes, and their different temperature dependence. Our work extends the study of coupled thermal and particle transport into unprecedented regimes, not reachable in natural condensed matter and atomic gas systems. △ Less

Submitted 31 July, 2023; originally announced July 2023.

Optical Dipole Structure and Orientation of GaN Defect Single-Photon Emitters

Authors: Yifei Geng, Debdeep Jena, Gregory D. Fuchs, Warren R. Zipfel, Farhan Rana

Abstract: GaN has recently been shown to host bright, photostable, defect single photon emitters in the 600-700 nm wavelength range that are promising for quantum applications. The nature and origin of these defect emitters remain elusive. In this work, we study the optical dipole structures and orientations of these defect emitters using the defocused imaging technique. In this technique, the far-field rad… ▽ More GaN has recently been shown to host bright, photostable, defect single photon emitters in the 600-700 nm wavelength range that are promising for quantum applications. The nature and origin of these defect emitters remain elusive. In this work, we study the optical dipole structures and orientations of these defect emitters using the defocused imaging technique. In this technique, the far-field radiation pattern of an emitter in the Fourier plane is imaged to obtain information about the structure of the optical dipole moment and its orientation in 3D. Our experimental results, backed by numerical simulations, show that these defect emitters in GaN exhibit a single dipole moment that is oriented almost perpendicular to the wurtzite crystal c-axis. Data collected from many different emitters shows that the angular orientation of the dipole moment in the plane perpendicular to the c-axis exhibits a distribution that shows peaks centered at the angles corresponding to the nearest Ga-N bonds and also at the angles corresponding to the nearest Ga-Ga (or N-N) directions. Moreover, the in-plane angular distribution shows little difference among defect emitters with different emission wavelengths in the 600-700 nm range. Our work sheds light on the nature and origin of these GaN defect emitters. △ Less

Submitted 29 June, 2023; originally announced June 2023.

Comments: 15 pages, 4 figures

Prediction of novel final phases in aged uranium-niobium alloys

Authors: Xiao L. Pan, Hao Wang, Lei L. Zhang, Yu F. Wang, Xiang R. Chen, Hua Y. Geng, Ying Chen

Abstract: Ordered intermetallics are long believed to be the final products of the aging of U-Nb solid solutions at low temperatures, a crucial property for the practical applications of this alloy in engineering and industry. However, such conjectured ordered compounds have not been experimentally or theoretically established. Herein, numerical evidence for ordered intermetallic U-Nb compounds is presented… ▽ More Ordered intermetallics are long believed to be the final products of the aging of U-Nb solid solutions at low temperatures, a crucial property for the practical applications of this alloy in engineering and industry. However, such conjectured ordered compounds have not been experimentally or theoretically established. Herein, numerical evidence for ordered intermetallic U-Nb compounds is presented using thorough first-principles structure predictions up to 500 GPa. Two stable U2Nb compounds and one metastable U2Nb and one metastable U3Nb were discovered. A unique hybridized transition driven by pressure was observed in U2Nb, which is a superposition of one first-order transition and another second-order transition, leading to striking features near the transition pressure of 21.6 GPa. The decomposition limit of these compounds at high temperature was also investigated. The strong stability of U2Nb in the region of low pressure and high temperature was revealed. This discovery of ordered U2Nb and its strong stability over a wide pressure range completely changed the phase diagram of U-Nb alloys and shed new light on the dynamic response and aging mechanism of U-Nb alloys. △ Less

Submitted 25 March, 2023; originally announced March 2023.

Comments: 21 pages, 16 figures, with Supplementary Material

Journal ref: Journal of Nuclear Materials 579 (2023) 154394

Phase regeneration of QPSK signals based on Kerr soliton combs in a highly nonlinear optical fiber

Authors: Xinjie Han, Yong Geng, Haocheng Ke, Kun Qiu

Abstract: We demonstrate an all-optical phase regeneration technique based on Kerr soliton combs, which can realize degraded quaternary phase shift keying (QPSK) signal regeneration through phase-sensitive amplification. A Kerr soliton comb is generated at the receiver side of optical communication systems based on a carrier recovery scheme and is used as coherent dual pumps to achieve phase regeneration. O… ▽ More We demonstrate an all-optical phase regeneration technique based on Kerr soliton combs, which can realize degraded quaternary phase shift keying (QPSK) signal regeneration through phase-sensitive amplification. A Kerr soliton comb is generated at the receiver side of optical communication systems based on a carrier recovery scheme and is used as coherent dual pumps to achieve phase regeneration. Our study will enhance the relay and reception performance of all-optical communication systems. △ Less

Submitted 26 March, 2023; v1 submitted 22 March, 2023; originally announced March 2023.

Comments: 8pages;5figures

Full Temperature-Dependent Potential and Anharmonicity in Metallic Hydrogen: Colossal NQE and the Consequences

Authors: Hua Y. Geng

Abstract: The temperature-dependent effective potential (TDEP) method for anharmonic phonon dispersion is generalized to the full potential case by combining with path integral formalism. This extension naturally resolves the intrinsic difficulty in the original TDEP at low temperature. The new method is applied to solid metallic hydrogen at high pressure. A colossal nuclear quantum effect (NQE) and subsequ… ▽ More The temperature-dependent effective potential (TDEP) method for anharmonic phonon dispersion is generalized to the full potential case by combining with path integral formalism. This extension naturally resolves the intrinsic difficulty in the original TDEP at low temperature. The new method is applied to solid metallic hydrogen at high pressure. A colossal nuclear quantum effect (NQE) and subsequent anharmonicity are discovered, which not only leads to unexpectedly large drift of protons, but also slows down the convergence rate substantially when computing the phonon dispersions. By employing direct ab initio path integral molecular dynamics simulations as the benchmark, a possible breakdown of phonon picture in metallic hydrogen due to colossal NQE is indicated, implying novel lattice dynamical phenomena might exist. Inspired by this observation, a general theoretical formalism for quantum lattice dynamics beyond phonon is sketched, with the main features being discussed. △ Less

Submitted 25 November, 2022; originally announced November 2022.

Comments: 35 pages, 9 figures, 1 table, with Supporting Information

Journal ref: J. Phys. Chem. C 2022, 126, 19355-19366

Lattice dynamics and elastic properties of alpha-U at high-temperature and high-pressure by machine learning potential simulations

Authors: Hao Wang, Xiao-Long Pan, Yu-Feng Wang, Xiang-Rong Chen, Yi-Xian Wang, Hua Y. Geng

Abstract: Studying the physical properties of materials under high pressure and temperature through experiments is difficult. Theoretical simulations can compensate for this deficiency. Currently, large-scale simulations using machine learning force fields are gaining popularity. As an important nuclear energy material, the evolution of the physical properties of uranium under extreme conditions is still un… ▽ More Studying the physical properties of materials under high pressure and temperature through experiments is difficult. Theoretical simulations can compensate for this deficiency. Currently, large-scale simulations using machine learning force fields are gaining popularity. As an important nuclear energy material, the evolution of the physical properties of uranium under extreme conditions is still unclear. Herein, we trained an accurate machine learning force field on alpha-U and predicted the lattice dynamics and elastic properties at high pressures and temperatures. The force field agrees well with the ab initio molecular dynamics (AIMD) and experimental results, and it exhibits higher accuracy than classical potentials. Based on the high-temperature lattice dynamics study, we first present the temperature-pressure range in which the Kohn anomalous behavior of the $Σ$4 optical mode exists. Phonon spectral function analysis showed that the phonon anharmonicity of alpha-U is very weak. We predict that the single-crystal elastic constants C44, C55, C66, polycrystalline modulus (E,G), and polycrystalline sound velocity ($C_L$,$C_S$) have strong heating-induced softening. All the elastic moduli exhibited compression-induced hardening behavior. The Poisson's ratio shows that it is difficult to compress alpha-U at high pressures and temperatures. Moreover, we observed that the material becomes substantially more anisotropic at high pressures and temperatures. The accurate predictions of alpha-U demonstrate the reliability of the method. This versatile method facilitates the study of other complex metallic materials. △ Less

Submitted 4 October, 2022; originally announced October 2022.

Comments: 21 pages, 9 figures, with Supplementary Material

Journal ref: Journal of Nuclear Materials 572, 154029 (2022)

MyElas: An automatized tool-kit for high-throughput calculation, post-processing and visualization of elasticity and related properties of solids

Authors: Hao Wang, Y. C. Gan, Hua Y. Geng, Xiang-Rong Chen

Abstract: Elasticity is one of the most fundamental mechanical properties of solid. In high-throughput design of advanced materials, there is an imperative demand for the capability to quickly calculate and screen a massive pool of candidate structures. A fully automatized pipeline with minimal human intervention is the key to provide high efficiency to achieve the goal. Here, we introduce a tool-kit MyElas… ▽ More Elasticity is one of the most fundamental mechanical properties of solid. In high-throughput design of advanced materials, there is an imperative demand for the capability to quickly calculate and screen a massive pool of candidate structures. A fully automatized pipeline with minimal human intervention is the key to provide high efficiency to achieve the goal. Here, we introduce a tool-kit MyElas that aims to address this problem by forging all pre-processing, elastic constant and other related property calculations, and post-processing into an integrated framework that automatically performs the assigned tasks to drive data flowing through parallelized pipelines from input to output. The core of MyElas is to calculate the second and third order elastic constants of a solid with the energy-strain method from first-principles. MyElas can auto-analyze the elastic constants, to derive other related physical quantities. Furthermore, the tool-kit also integrates a visualization function, which can, for example, plot the spatial anisotropy of elastic modulus and sound velocity of monocrystalline. The validity and efficiency of the toolkit are tested and bench-marked on several typical systems. △ Less

Submitted 4 October, 2022; originally announced October 2022.

Comments: 31 pages, 8 figures

Journal ref: Computer Physics Communications 281, 108495 (2022)

$^{197}$Au($γ,\,xn;\,x\,=\,1\thicksim9$) Reaction Cross Section Measurements using Laser-Driven Ultra-Intense $γ$-Ray Source

Authors: D. Wu, H. Y. Lan, J. Y. Zhang, J. X. Liu, H. G. Lu, J. F. Lv, X. Z. Wu, H. Zhang, J. Cai, Q. Y. Ma, Y. H. Xia, Z. N. Wang, M. Z. Wang, Z. Y. Yang, X. L. Xu, Y. X. Geng, Y. Y. Zhao, C. Lin, W. J. Ma, J. Q. Yu, H. R. Wang, F. L. Liu, C. Y. He, B. Guo, P. Zhu , et al. (4 additional authors not shown)

Abstract: We present a new method for the measurements of photonuclear reaction flux-weighted average cross sections and isomeric ratios using a laser-driven bremsstrahlung $γ$-ray source. An ultra-bright ultra-fast 60$\,\thicksim\,$250 MeV bremsstrahlung $γ$-ray source was established using the 200 TW laser facility in the Compact Laser Plasma Accelerator Laboratory, Peking University, which could cover th… ▽ More We present a new method for the measurements of photonuclear reaction flux-weighted average cross sections and isomeric ratios using a laser-driven bremsstrahlung $γ$-ray source. An ultra-bright ultra-fast 60$\,\thicksim\,$250 MeV bremsstrahlung $γ$-ray source was established using the 200 TW laser facility in the Compact Laser Plasma Accelerator Laboratory, Peking University, which could cover the energy range from knocking out neutrons to producing pions. Stable quasi-monoenergetic electron beams were generated via laser wakefield acceleration with a charge of 300$\,\thicksim\,$600 pC per shot. The averaged $γ$-ray intensities ($\geqslant$8 MeV) were higher than 10$^{8}$ per shot and the instantaneous intensities can reach above 10$^{19}$ s$^{-1}$ with a duration time about 6.7 ps. $^{65}$Cu($γ,\,n$)$^{64}$Cu and $^{27}$Al($γ,\,x$)$^{24}$Na reactions were used as $γ$-ray flux monitors in the experiments. The flux-weighted average cross sections and isomeric ratios of $^{197}$Au($γ,\,xn;\,x\,=\,1\thicksim9$) reactions were analyzed through activation measurements. The results showed good agreement with previous works and proved this method to be accurate. The $^{197}$Au($γ,\,xn;\,x\,=\,7\thicksim\,9$) reaction cross sections were first achieved with the highest threshold energy of 71.410 MeV. Theoretical cross sections of TALYS 1.9 were calculated to compare with experiment results. This method offered a unique way of gaining insight into photonuclear reaction research, especially for short-lived isomers which extremely lack experimental data. △ Less

Submitted 23 November, 2023; v1 submitted 28 September, 2022; originally announced September 2022.

Alpha-particle generation from H-11B fusion initiated by laser-accelerated boron ions

Authors: Defeng Kong, Shirui Xu, Yinren Shou, Ying Gao, Zhusong Mei, Zhuo Pan, Zhipeng Liu, Zhengxuan Cao, Yulan Liang, Ziyang Peng, Pengjie Wang, Di Luo, Yang Li, Zhi Li, Huasheng Xie, Guoqiang Zhang, Wen Luo, Jiarui Zhao, Shiyou Chen, Yixing Geng, Yanying Zhao, Jianming Xue, Xueqing Yan, Wenjun Ma

Abstract: Here we report the generation of MeV alpha-particles from H-11B fusion initiated by laser-accelerated boron ions. Boron ions with maximum energy of 6MeV and fluence of 10^9/MeV/sr@5MeV were generated from 60-nm-thick self-supporting boron nanofoils irradiated by 1J femtosecond pulses at an intensity of 10^19W/cm^2. By bombarding secondary hydrogenous targets with the boron ions, 3*10^5/sr alpha-pa… ▽ More Here we report the generation of MeV alpha-particles from H-11B fusion initiated by laser-accelerated boron ions. Boron ions with maximum energy of 6MeV and fluence of 10^9/MeV/sr@5MeV were generated from 60-nm-thick self-supporting boron nanofoils irradiated by 1J femtosecond pulses at an intensity of 10^19W/cm^2. By bombarding secondary hydrogenous targets with the boron ions, 3*10^5/sr alpha-particles from H-11B fusion were registered, which is consistent with the theoretical yield calculated from the measured boron energy spectra. Our results demonstrate an alternative way toward ultrashort MeV alpha-particle sources employing compact femtosecond lasers. The ion acceleration and product measurement scheme are referential for the studies on the ion stopping power and cross-section of the H-11B reaction in solid or plasma. △ Less

Submitted 11 September, 2022; originally announced September 2022.

Journal ref: Laser Part. Beams 2022 (2022) e7

Wavelength-division multiplexing communications using integrated soliton microcomb laser source

Authors: Yong Geng, Yanlan Xiao, Qingsong Bai, Xinjie Han, Wenchan Dong, Wenting Wang, Jinggu Xue, Baicheng Yao, Guangwei Deng, Qiang Zhou, Kun Qiu, Jing Xu, Heng Zhou

Abstract: In this Letter, we investigate the feasibility and performance of wavelength division multiplexed (WDM) optical communications using an integrated dissipative Kerr soliton micro-comb as the multi-channel laser source. First, we confirm that soliton microcomb pumped directly by a DFB laser self-injection locked to the host micro-cavity has sufficiently low frequency and amplitude noises to encode a… ▽ More In this Letter, we investigate the feasibility and performance of wavelength division multiplexed (WDM) optical communications using an integrated dissipative Kerr soliton micro-comb as the multi-channel laser source. First, we confirm that soliton microcomb pumped directly by a DFB laser self-injection locked to the host micro-cavity has sufficiently low frequency and amplitude noises to encode advanced data formats. Second, perfect soliton crystals are exploited to boost the power level of each microcomb line, so that they can be directly used for data modulation excluding pre-amplification. Third, in a proof-of-concept experiment we demonstrate 7-channel 16-QAM data transmissions using an integrated perfect soliton microcomb as the laser carriers, excellent data receiving performances are obtained under various fiber link distances and amplifier configurations. Our study reveals that fully integrated Kerr soliton microcombs are viable and advantageous for optical data communications. △ Less

Submitted 1 June, 2022; originally announced June 2022.

Polarization multiplexed dissipative Kerr solitons in on-chip micro-resonator

Authors: Yong Geng, Yanlan Xiao, Xinjie Han, Kun Qiu, Jing Xu, Heng Zhou

Abstract: We demonstrate polarization multiplexed dissipative Kerr solitons in an on-chip silicon nitride micro-resonator. In our experiment, TE- and TM-polarized soliton can be individually generated and controlled, thanks to their weak mutual interaction as the result of sufficiently different repetition rates and orthogonal polarization states. Furthermore, we find that TE- and TM-polarized solitons usua… ▽ More We demonstrate polarization multiplexed dissipative Kerr solitons in an on-chip silicon nitride micro-resonator. In our experiment, TE- and TM-polarized soliton can be individually generated and controlled, thanks to their weak mutual interaction as the result of sufficiently different repetition rates and orthogonal polarization states. Furthermore, we find that TE- and TM-polarized solitons usually exhibit uncorrelated time jitters, therefore the frequency and phase coherence between the polarization multiplexed soliton microcombs change dramatically as a function of pump laser parameters, by optimizing which we achieve narrow dual-microcomb beat note linewidth as small as 4.4 kHz. Potential applications of on-chip polarization multiplexed soliton microcombs include Kerr comb spectral expansion, dual-comb metrology, and measurement of quantum entanglements. △ Less

Submitted 30 May, 2022; v1 submitted 26 May, 2022; originally announced May 2022.

Mamba: a systematic software solution for beamline experiments at HEPS

Authors: Yu Liu, Yan-Da Geng, Xiao-Xue Bi, Xiang Li, Ye Tao, Jian-She Cao, Yu-Hui Dong, Yi Zhang

Abstract: To cater for the diverse experiment requirements at the High Energy Photon Source (HEPS) with often limited human resources, Bluesky is chosen as the basis for our software framework, Mamba. In our attempt to address Bluesky's lack of integrated GUIs, command injection with feedback is chosen as the main way for the GUIs to cooperate with the CLI; a RPC service is provided, which also covers funct… ▽ More To cater for the diverse experiment requirements at the High Energy Photon Source (HEPS) with often limited human resources, Bluesky is chosen as the basis for our software framework, Mamba. In our attempt to address Bluesky's lack of integrated GUIs, command injection with feedback is chosen as the main way for the GUIs to cooperate with the CLI; a RPC service is provided, which also covers functionalities unsuitable for command injection, as well as pushing of status updates. In order to fully support high-frequency applications like fly scans, Bluesky's support for asynchronous control is being improved; to support high-throughput experiments, Mamba Data Worker (MDW) is being developed to cover the complexity in asynchronous online data processing for these experiments. To systematically simplify the specification of metadata, scan parameters and data-processing graphs for each type of experiments, an experiment parameter generator (EPG) will be developed; experiment-specific modules to automate preparation steps will also be made. The integration of off-the-shelf code in Mamba for domain-specific needs is under investigation, and Mamba GUI Studio (MGS) is being developed to simplify the implementation and integration of GUIs. △ Less

Submitted 28 March, 2022; originally announced March 2022.

Comments: 9 pages, 6 figures, accepted for J. Synchrotron Rad

Journal ref: J. Synchrotron Rad. 2022, 29(3), 664-669

Evidence for mechanical softening-hardening dual anomaly in transition metals from shock compressed vanadium

Authors: Hao Wang, J. Li, X. M. Zhou, Y. Tan, L. Hao, Y. Y. Yu, C. D. Dai, K. Jin, Q. Wu, Q. M. Jing, X. R. Chen, X. Z. Yan, Y. X. Wang, Hua Y. Geng

Abstract: Solid usually becomes harder and tougher under compression, and turns softer at elevated temperature. Recently, compression-induced softening and heating-induced hardening (CISHIH) dual anomaly was predicted in group VB elements such as vanadium. Here, the evidence for this counterintuitive phenomenon is reported. By using accurate high-temperature high-pressure sound velocities measured at Hugoni… ▽ More Solid usually becomes harder and tougher under compression, and turns softer at elevated temperature. Recently, compression-induced softening and heating-induced hardening (CISHIH) dual anomaly was predicted in group VB elements such as vanadium. Here, the evidence for this counterintuitive phenomenon is reported. By using accurate high-temperature high-pressure sound velocities measured at Hugoniot states generated by shock-waves, together with first-principles calculations, we observe not only the prominent compression-induced sound velocity reduction, but also strong heating-induced sound velocity enhancement, in shocked vanadium. The former corresponds to the softening in shear modulus by compression, whereas the latter reflects the reverse hardening by heat. These experiments also unveil another anomaly in Young's modulus that wasn't reported before. Based on the experimental and theoretical data, we infer that vanadium might transition from BCC into two different rhombohedral (RH1 and RH2) phases at about 79GPa and 116GPa along the Hugoniot, respectively, which implies a dramatic difference in static and dynamic loading, as well as the significance of deviatoric stress and rate-relevant effects in high-pressure phase transition dynamics. △ Less

Submitted 31 January, 2022; originally announced January 2022.

Comments: 43 pages, 16 figures, with Supplementary Material

Journal ref: Physical Review B 104, 134102 (2021)