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MnBi2Te4 can generate a variety of exotic topological quantum states, which are closely related to its special structure. We conduct comprehensive multiple-cycle high-pressure research on MnBi2Te4 by using a diamond anvil cell to study its phase transition behaviors under high pressure. As observed, when the pressure does not exceed 15 GPa, the material undergoes an irreversible metal–semiconductor–metal transition, whereas when the pressure exceeds 17 GPa, the layered structure is damaged and becomes irreversibly amorphous due to the lattice distortion caused by compression, but it is not completely amorphous, which presents some nano-sized grains after decompression. Our investigation vividly reveals the phase transition behaviors of MnBi2Te4 under high pressure cycling and paves the experimental way to find topological phases under high pressure. [ABSTRACT FROM AUTHOR]

Nonlayered palladium sulfide (PdS) is of interest due to its rich physical properties and promising applications in optoelectronic devices. However, the growth of thin nonlayered PdS remains challenging because of its intrinsic 3D lattice structure. Here, the first demonstration of the direct synthesis of thin rectangular PdS ribbons/flakes on SiO2/Si substrates by a facile chemical vapor deposition (CVD) approach is presented. The atomic structure and high crystalline quality of CVD‐derived PdS crystals are shown by scanning transmission electron microscopy. The nonlinear saturable absorption and absorption enhancement are revealed by using ultrafast optical pump‐probe spectroscopy, and the photocarrier dynamics present the hot phonon bottleneck and Auger recombination effects. Additionally, the Raman vibration modes display the polarization‐dependent properties verified by angle‐resolved polarized Raman spectroscopy. Importantly, the photodetector based on PdS ribbon demonstrates a decent photoresponsivity of ≈7.7 × 103 A W−1. These results provide an effective way to form thin nonlayered PdS with potential applications in the field of photodetection. [ABSTRACT FROM AUTHOR]

Terahertz (THz) time-domain spectroscopy (THz-TDS) of polycrystalline MnCr2O4 was performed at <9 T and low temperatures. A resonance absorption in the sub-THz range with linear blueshifts was observed as the magnetic field was increased from 4 T to 9 T. These magnetism-driven absorptions originated from a ferromagnetic resonance, which agrees with low-field electron spin resonance measurements and ferromagnetic resonance theory. The low-temperature g -factors of MnCr2O4 were also obtained using THz-TDS. This work provides new insights into the spin dynamics of chromite spinel compounds in the THz region. [ABSTRACT FROM AUTHOR]

The emerging two-dimensional (2D) platinum disulfide (PtS2) has driven increasing attentions due to its high electron mobility, good air-stability, and strong interlayer interaction which leads to a widely tunable electronic structure. However, a detailed study on its covalent-like layer-dependent properties remains infant. Herein, we demonstrate the successful production of ultrathin 1T-PtS2 ribbons with thickness centralized almost at monolayer 1L–4L and large domain size up to 210 µm on Au foils using chemical vapor deposition (CVD) technique, which enables macro- and microscopic study of its extraordinary layer-dependent features with precise control of the number of layers. Using electron energy loss spectroscopy (EELS) and optical pump-probe spectroscopy (OPPS), we reveal that both the electron and ultrafast optical absorption signals of the as-grown 2D PtS2 show strong nonlinear layer-dependent responses which manifest discriminated transition in 1L–4L PtS2 ribbons. The layer-dependent nonlinear response of 2D PtS2 can be well interpreted in the frame of calculated electron and phonon structures. These achievements offer a platform for successfully fabricating large-sized ultrathin 2D PtS2 and facilitating our knowledge about its electronic and optoelectronic properties. [ABSTRACT FROM AUTHOR]

We employ polarization-resolved femtosecond optical pump–probe spectroscopy to investigate the nonequilibrium photocarrier dynamics in excitonic insulator Ta2NiSe5. The electronic dynamics, including hot carrier cooling, exciton formation, and recombination in the timescale ranging from subpicoseconds to a few tens of picoseconds, have been established from the transient reflectivity spectra, showing strong in-plane anisotropy with respect to the probe polarization. Such anisotropic photocarrier dynamics possibly arise from the crystalline orientation dependence of the excitonic polarizability. Furthermore, we find that the amplitude of coherent phonons with a frequency of 1 THz is subject to the probe polarization, whereas it is not sensitive to the pump polarization. This substantiates that the displacive excitation of coherent phonons plays a decisive role in lattice dynamics. In addition, we find that the photo-induced dielectric screening tends to suppress the amplitude of coherent phonons with increasing pump fluence, manifesting a remarkable polarization dependence. Our work provides valuable insights into the excitonic dynamics and the origin of coherent phonon generation and also may contribute to the development of polarization-sensitive photoelectric devices based on Ta2NiSe5. [ABSTRACT FROM AUTHOR]

A systemic investigation of the terahertz (THz) transmission of La0.67Ca0.33MnO3 film on the (001)-oriented NdGaO3 substrate under external magnetic field and low temperature have been performed. The significant THz absorption difference between the out-of-plane and the in-plane magnetic field direction is observed, which is consistent with the electrical transport measurement using the standard four-probe technique. Furthermore, we find that the complex THz conductivities can be reproduced in terms of the Drude Smith equation as the magnetic field is perpendicular to the film plane, whereas it deviates from this model when the in-plane magnetic field is applied. We suggest that such anisotropies in THz transport dynamics have close correspondences with the phase separation and anisotropic magnetoresistance effects in the perovskite-structured manganites. Our work demonstrates that the THz time-domain spectroscopy (TDS) can be an effective non-contact method for studying the magneto-transport properties of the perovskite-structured manganites. [ABSTRACT FROM AUTHOR]