Abstract The two-dimensional van der Waals ferromagnetic semiconductor CrI 3 provides an ideal platform for exploring the interplay among structural, electronic, and magnetic degrees of freedom. In this work, we systematically investigate the thickness-dependent optical properties of 5-layer and 10-layer CrI 3 under hydrostatic pressure up to 27.9 GPa by in situ Raman and UV-visible absorption spectroscopy. All A g Raman modes exhibit a continuous blueshift with increasing pressure. The low-frequency modes ( A g 1 - A g 3 ) are mainly associated with enhanced interlayer coupling, whereas the high-frequency modes ( A g 4 - A g 6 ) reflect the suppression of surface vibrations. The Raman modes disappear at approximately 4.9 GPa for the 5-layer sample and 11.2 GPa for the 10-layer sample, indicating a stronger strain sensitivity in thinner CrI 3 . Optical absorption measurements show a pronounced redshift of the absorption edge, accompanied by bandgap narrowing from 2.26 eV to 1.26 eV in the 5-layer CrI 3 . At comparable pressures, the 5-layer sample consistently exhibits a wider bandgap than the 10-layer one, which is attributed to quantum confinement effects and reduced interlayer hybridization. Above 12.7 GPa, the bandgap reduction becomes less pronounced, likely due to enhanced Cr 3d /I- 5p orbital overlap and strengthened superexchange interactions. These results reveal a clear layer-dependent structure-electronic coupling in CrI 3 under compression and provide useful insights into pressure modulation of van der Waals magnetic semiconductors.

Abstract Titanium-boron (Ti-B) compounds exhibit great promise as superhard materials due to titanium's low atomic mass and abundant valence electrons. In this work, we systematically investigated the crystal structures of TiB 6 under pressures ranging from 0 to 100 GPa using the CALYPSO algorithm combined with first-principles calculations. Phonon dispersion analysis and elastic constant evaluations confirm the dynamic and mechanical stability of five predicted TiB 6 structures. Notably, the α- Amm 2-TiB 6 structure was predicted to have a remarkable Vickers hardness of 56 GPa, as estimated by Chen’s empirical model. All five structures are thermodynamically stable under ambient conditions, suggesting viable synthetic pathways. Their outstanding bulk moduli and ultrahigh hardness further classify them as potential incompressible and superhard materials. These theoretical insights lay a robust foundation for future experimental synthesis efforts.

Abstract The pressure-induced structural transformation in metallic glass (MG) is a challenging and important subject in condensed matter physics. In the present first-principles molecular dynamics study, atomic packing of the La 75 Al 25 MG under pressure was investigated and the structure was predicted to crystallize at 92 GPa. It is found that the distributions of La and Al atoms are not homogeneous, as often anticipated. Especially, Al atoms form aggregates in the glass structure with strong covalent characteristic of the Al-Al bonds. The pressure-induced crystallization was not only caused by the dominant packing of the larger La atoms but is also facilitated by the presence of these rigid Al clusters.

Abstract Attosecond light sources serve as crucial tools for investigating the ultrafast electronic dynamics in matter with remarkable temporal resolution. Traditional methods face difficulties in accurately measuring attosecond pulses, and the prevailing approach involves utilizing attosecond streak cameras coupled with inversion algorithms to reconstruct phase information. However, these algorithms often require multiple iterations and extensive computational time. This study investigates the utilization of autocorrelation graphs as inputs for a convolutional neural network (CNN) to invert streaking traces obtained by attosecond streak camera. We explore the noise resistance capability of autocorrelation within the CNN inversion and aim to provide a physical explanation for its effectiveness. The objective of this research is to enhance the accuracy and reliability of CNN inversion for attosecond streaking traces, enabling improved resilience against experimental noises.

Abstract Interlayer excitons (IXs) in two-dimensional (2D) van der Waals heterostructures have attracted considerable attention due to their unique optical and electronic properties. Owing to the spatially indirect nature, the radiative emission efficiency highly sensitive to interlayer twist angles. Further considering that their uniformly oriented out-of-plane dipole moments limit directional emission, strategies to simultaneously improve emission efficiency and induce optical anisotropy warrant indepth investigation. In this work, we report significant photoluminescence (PL) enhancement and optical anisotropy of IXs in 2L-MoSe 2 /perovskite heterostructures mediated by energy transfer from ReS 2 . We attribute this enhancement to Förster resonance energy transfer (FRET), which increases the 2L-MoSe 2 emission by approximately eight-fold at room temperature, and nearly doubles the emission intensity of momentum-indirect IXs in 2L-MoSe 2 /perovskite heterostructures at 78 K. Importantly, the optical anisotropy of ReS 2 can be effectively imprinted onto 2L-MoSe 2 and associated indirect IXs during the energy transfer process, yielding a linear dichroism of approximately 1.1 for both intralayer excitons and IXs with identical polarization directions. These findings expand the scope of IX study beyond direct bandgap materials with strong intrinsic emission to include systems with indirect bandgaps, offering new avenues for realizing high-performance polarization-sensitive optoelectronic devices.

Abstract Rare-earth nickelate ( Re NiO 3 , with Re ≠ La) constitute a paradigmatic class of strongly correlated electron systems, exhibiting a remarkable tunability of the metal-insulator transition (MIT) in response to external stimuli such as hydrostatic pressure, temperature, and chemical doping. This tunability arises from the competitive interplay of charge, spin, and orbital degrees of freedom. However, the fundamental mechanisms governing effective MIT control under extreme conditions, particularly the intricate coupling between lattice dynamics and electronic localization, remain elusive. This knowledge gap poses a significant challenge to both fundamental research and practical applications of these materials. Herein, we present a systematic investigation of the structural phase transitions and electrical transport properties of HoNiO 3 under extreme conditions. In situ high pressure X-ray diffraction (XRD) analysis uncovers a structural evolution pathway: an initial transition from a monoclinic insulating phase ( P 2 1 / n ) to an orthorhombic metallic phase ( Pbnm ) at approximately 17 GPa, followed by the emergence of a mixed-phase region ( Pbnm and R 3 c ) at approximately 35 GPa. Complementary electrical transport measurements reveal a pronounced sensitivity of the metal-insulator transition temperature ( T MIT ) to the synergistic effects of high pressure and low temperature. These findings not only furnish crucial experimental evidence for elucidating the structure-property relationship in HoNiO 3 under extreme conditions, but also lay a conceptual foundation for designing advanced functional devices based on Re NiO 3 materials, with promising applications in high-sensitivity pressure sensors and temperature-responsive switches featuring tunable activation thresholds.

Abstract In this work, carrier modulation in beta-Gallium Oxide ( β -Ga 2 O 3 ) films through an oxygen annealing method is systematically investigated, including annealing time and annealing cap layer (ACL) design. Capacitance-voltage measurement conducted on vertical SBD structures was used to evaluate the carrier concentration after annealing. The formation of “surface layer” may suppress the diffusion of oxygen species as the annealing time increases. An 8-hour annealing time resulted in a carrier modulation with an approximately 3-µm-deep low-carrier-concentration layer. The annealing cap layer, consisting of poly-Si and SiO 2 , was deposited and patterned to achieve area-selective carrier modulation in β -Ga 2 O 3 . The effective thickness of poly-Si for blocking oxygen diffusion was confirmed by scanning electron microscopy (SEM) for the first time. A definite thickness of SiO 2 served as both etching stop layer and lift-off layer for poly-Si. According to simulation results, the non-ideal surface caused extra high peak electric field in the β -Ga 2 O 3 device. A combination of an optimized dry etching method and low-compressive-stress deposition technology was employed to eliminate the bird's beak-like shape structure that appeared at the edges of the patterns and bulges on the β -Ga 2 O 3 surface after annealing. The feasibility of the carrier modulation technology enables the diversity of β -Ga 2 O 3 devices fabrication.

Abstract Elucidating how magnetic interactions are established in high-temperature superconductors is crucial for resolving the long-standing puzzle of the superconducting pairing mechanism. However, for iron-based superconductors, due to the diversities of their magnetic and electronic structures, the mechanism of magnetic interactions remains controversial. Here, we employed in-situ alkali-metal deposition and uniaxial strain to tune the four-fold (C4) magnetic phase in Sr0.64Na0.36Fe2As2 and utilized angle-resolved photoemission spectroscopy (ARPES) to probe the response of its electronic structure. We found that the alkali-metal deposition suppresses the C4 magnetic phase effectively, driving the system into a stripe spin density wave phase with two-fold rotational (C2) symmetry. Counterintuitively, the uniaxial strain that naturally breaks the C4 rotational symmetry of the lattice exerts only a limited suppressive effect on the C4 magnetic phase. While the sensitivity of C4 magnetic phase to electron doping implies that the orbital selectivity of Fermi surface nesting plays a critical role in determining the magnetic configuration, validating the contribution of itinerant electrons in mediating the magnetic fluctuations, the insensitivity of the C4 magnetic phase to uniaxial strain suggests that the nematic order exhibits no intermediate correlation with the magnetism in iron-based superconductors. Our results provide crucial clues for a comprehensive understanding of the complex phase diagram of iron-based superconductors.