Accepted Manuscripts

Atomistic modeling is a widely employed theoretical method of computational materials science. It has found particular utility in the study of magnetic materials. Initially, magnetic empirical interatomic potentials or spinpolarized density functional theory (DFT) served as the primary models for describing interatomic interactions in atomistic simulations of magnetic systems. Furthermore, in recent years, a new class of interatomic potentials known as magnetic machine-learning interatomic potentials (magnetic MLIPs) has emerged. These MLIPs combine the computational efficiency, in terms of CPU time, of empirical potentials with the accuracy of DFT calculations. In this review, our focus lies on providing a comprehensive summary of the interatomic interaction models developed specifically for investigating magnetic materials. We also delve into the various problem classes to which these models can be applied. Finally, we offer insights into the future prospects of interatomic interaction model development for the exploration of magnetic materials.

Graphene (Gr) with widely acclaimed characteristics, such as exceptionally long spin diffusion length at room temperature, provides an outstanding platform for spintronics. However, its inherent weak spin-orbit coupling (SOC) has limited its efficiency for generating the spin currents in order to control the magnetization switching process for the application in spintronics memories. Following the theoretical prediction on the enhancement of SOC in Gr by heavy atoms adsorption, here we experimentally observe a sizeable spin-orbit torques (SOTs) in Gr by the decoration of its surface with Pt adatoms in Gr/Pt(t_Pt)/FeNi trilayers with the optimal damping-like SOT efficiency around 0.55 by 0.6-nm-thick Pt layer adsorption. The value is nearly four times larger than that of the Pt/FeNi sample without Gr and nearly twice as large as that of the Gr/FeNi sample without Pt adsorption. The efficiency of the enhanced SOT in Gr by Pt adatoms is also demonstrated by the field-free SOT magnetization switching process with a relatively low critical current density around 5.4 MA/cm² in Gr/Pt/FeNi trilayers with the in-plane magnetic anisotropy. These findings pave the way for Gr spintronics application, offering solutions for future low power consumption memories.

The Clauser-Horne-Shimony-Holt (CHSH) game provides a captivating illustration of the advantages of quantum strategies over classical ones. In a recent study, a variant of the CHSH game leveraging a single qubit system, referred to as the CHSH^* game, has been identified. We demonstrate that this mapping relationship between these two games remains effective even for a non-unitary gate. In this context, we delve into the breach of Tsirelson's bound in a nonHermitian system, predicting changes in the upper and lower bounds of the player's winning probability when employing quantum strategies in a single dissipative qubit system. We experimentally explore the impact of the CHSH^* game on the player's winning probability in a single trapped-ion dissipative system, demonstrating a violation of Tsirelson's bound under the influence of parity-time (PT) symmetry. These results contribute to a deeper understanding of the influence of non-Hermitian systems on quantum games and the behavior of quantum systems under PT symmetry, which is crucial for designing more robust and efficient quantum protocols.

The Cs₂NaInCl₆ double perovskite is one of the most promising lead-free perovskites due to its exceptional stability and straightforward synthesis. However, it faces challenges related to inefficient photoluminescence. Doping and high-pressure are employed to tailor the optical properties of Cs₂NaInCl₆. Herein, Sb³⁺ doped Cs₂NaInCl₆ (Sb³⁺:Cs₂NaInCl₆) was synthesized and exhibits blue emission with a photoluminescence quantum yield of up to 37.3%. Further, by employing pressure tuning, a blue stable emission under a very wide range from 2.7 GPa to 9.8 GPa, for the first time, realized in Sb³⁺:Cs₂NaInCl₆. Subsequently, the emission intensity of Sb³⁺:Cs₂NaInCl₆ experiences a significant increase (3.3-times) at 19.0 GPa. We reveal that the pressure-induce the distinct emissions can be attributed to the carrier self-trapping and detrapping between Cs₂NaInCl₆ and Sb³⁺. Notably, the lattice compression in the cubic phase inevitably modify the band gap of Sb³⁺:Cs₂NaInCl₆. Our findings provide valuable insights into the effects of the high pressure in further boosting unique emission characteristics but also offer promising opportunities for the development of doped double perovskites with enhanced optical functionalities.

Two-dimensional (2D) topological materials have recently garnered significant interest due to their profound physical properties and promising applications for future quantum nanoelectronics. Achieving various topological states within one type of materials is, however, seldom reported. Based on first-principles calculations and tight-binding models, we investigate topological electronic states in a novel family of 2D halogenated tetragonal stanene (T-SnX, X = F, Cl, Br, I). All the four monolayers are found being unusual topological nodal-line semimetals (NLSs), protected by a glide mirror symmetry. When spin-orbit coupling (SOC) is turned on, T-SnF and TSnCl are still ascertained as topological NLSs due to the remaining band inversion, primarily composed of Sn p_xy orbitals, while T-SnBr and T-SnI become quantum spin Hall insulators. The phase transition is ascribed to moving up in energy of Sn s orbitals and increasing of SOC strengths. The topology origin in the materials is uniformly rationalized through elementary band representations. The robust and diverse topological states found in the 2D T-SnX monolayers position them as an excellent material platform for the development of innovative topological electronics.

Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high-Tc superconductors. In iron-based superconductors, spin excitations at low energy range, especially the spinresonance mode at E_R~5k_BT_c, are important for understanding the superconductivity. Here, we use inelastic neutron scattering (INS) to investigate the symmetry and in-plane wave-vector dependence of low-energy spin excitations of uniaxial-strain detwinned FeSe. The low-energy spin excitations (E ＜ 10 meV) appear mainly at Q = (±1; 0) in the superconducting state (T ≲ 9 K) and the nematic state (T ≲ 90 K), confirming the constant C₂ rotational symmetry and ruling out the C₄ mode at E ≈ 3 meV reported in a prior INS study. Moreover, our results reveal an isotropic spin resonance in the superconducting state, which is consistent with the s^± wave pairing symmetry. At slightly higher energy, low-energy spin excitations become highly anisotropic. The full width at half maximum (FWHM) of spin excitations is elongated along the transverse (TR) direction. The Q-space isotropic spin resonance and highly anisotropic low-energy spin excitations could arise from d_yz intraorbital selective Fermi surface nesting between the hole pocket around Γ point and the electron pockets centered at M_X point.

A hypothetical photon mass, $m_{\gamma}$, can produce a frequency-dependent vacuum dispersion of light, which leads to an additional time delay between photons with different frequencies when they propagate through a fixed distance. The dispersion measure--redshift measurements of fast radio bursts (FRBs) have been widely used to constrain the rest mass of the photon. However, all current studies analyzed the effect of the frequency-dependent dispersion for massive photons in the standard $\Lambda$CDM cosmological context. In order to alleviate the circularity problem induced by the presumption of a specific cosmological model based on the fundamental postulate of the masslessness of photons, here we employ a new model-independent smoothing technique, Artificial Neural Network (ANN), to reconstruct the Hubble parameter $H(z)$ function from 34 cosmic-chronometer measurements. By combining observations of 32 well-localized FRBs and the $H(z)$ function reconstructed by ANN,we obtain an upper limit of $m_{\gamma} \le 3.5 \times 10^{-51}\;\rm{kg}$, or equivalently $m_{\gamma} \le 2.0 \times 10^{-15}\;\rm{eV/c^2}$ ($m_{\gamma} \le 6.5 \times 10^{-51}\;\rm{kg}$, or equivalently $m_{\gamma} \le 3.6 \times 10^{-15}\;\rm{eV/c^2}$) at the $1\sigma$ ($2\sigma$) confidence level. This is the first cosmology-independent photon mass limit derived from extragalactic sources.

Rare-earth-free Mn-based binary alloy L1₀-MnAl with bulk perpendicular magnetic anisotropy (PMA) holds promise for high-performance magnetic random-access memory (MRAM) devices driven by spin-orbit torque (SOT). However, the lattice-mismatch issue makes it challenging to place the conventional spin current sources, such as heavy metals, between the L1₀-MnAl layer and substrate. In this work, we propose a solution by using the B2-CoGa alloy as the spin current source. The lattice-matching enables high-quality epitaxial growth of 2-nm-thick L1₀-MnAl on B2-CoGa, and the L1₀-MnAl exhibits a large PMA constant of 1.04×10⁶ J/m³. Subsequently, the considerable spin Hall effect in B2-CoGa enables the achievement of SOT-induced deterministic magnetization switching. Moreover, we have quantitatively determined the SOT efficiency in the bilayer. Furthermore, we have designed an L1₀-MnAl/B2-CoGa/Co₂MnGa structure to achieve field-free magnetic switching. Our results offer valuable insights for achieving high-performance SOT-MRAM devices based on L1₀-MnAl alloy

The quantum anomalous Hall (QAH) insulator has highly potential applications in spintronic device. However, the available candidate with tunable Chern numbers and high working temperature is quite rare. Here, we predicted 1T-PrN2 monolayer as a stable QAH insulator with high magnetic transition temperature above 600 K and tunable high Chern numbers of C = ±3 from first-principles. Without spin-orbit coupling (SOC), 1T-PrN₂ monolayer is predicted as a p-state Dirac half metal(DHM) with high Fermi velocity. Rich topological phases depending on the magnetization directions can be found when the SOC is considered. The QAH effect with periodical changes of Chern number (±1) can be produced when the magnetic moment breaks all twofold rotational symmetries in the xy plane. And the critical state can be identified as Weyl half semimetals (WHSMs). When the magnetization direction is parallel to the z-axis, the system exhibits high Chern number QAH effect with C = ±3. Our work provide a new material for exploring the novel QAH effect and developing high-performance topological devices.

We study superradiant phase transitions in a hybrid system of a two-dimensional Bose-Einstein condensate of atoms and two cavities arranged with a tilt angle. By adjusting the loss rate of cavities, we map out the phase diagram of steady states within a mean field framework. We find that when the loss rates of the two cavities are different, superradiant transitions may not occur at the same time in the two cavities. A first-order phase transition is observed between the states with only one cavity in superradiance and both in superradiance. In the case of both cavities are superradiant, a net photon current is observed flowing from the cavity with small decay rate to the one with large decay rate. The photon current shows a non-monotonic dependence on the loss rate difference, owing to the competition of photon number difference and cavity field phase difference. Our findings can be realized and detected in experiments.