Charge density wave (CDW) systems have been widely studied and proposed to be potential candidates for next‐generation electronic devices. However, the lack of room‐temperature CDW materials has limited the development of CDW‐based electronic devices, and thus finding a way to manipulate the CDW transitions and orders toward room temperature will be of importance. Room‐temperature and above CDW transition in 1T‐VSe2 is reported. The CDW transition is found to shift to ≈114 K at 0.7 GPa, and further compression enhances the transition temperature dramatically, reaching ≈358 K at 14.6 GPa. High‐pressure Raman spectroscopy measurement confirms that room‐temperature CDW order is achieved and persists up to 15 GPa. Such significant enhancement in CDW can be attributed to the pressure enhanced out‐of‐plane Fermi surface nesting and CDW gap in 1T‐VSe2. The observation of room‐ and high‐temperature CDW transition in 1T‐VSe2 under pressure provides an engineering approach to optimizing the CDW as needed in applications, which does not only open up a new platform for searching and controlling novel states of two‐dimensional materials, but also promotes a practical development of CDW‐related technology and devices.

Two-dimensional van der Waals (vdW) magnetic materials have emerged as possible candidates for future ultrathin spintronic devices, and finding a way to tune their physical properties is desirable for wider applications. Owing to the sensitivity and tunability of the physical properties to the variation of interatomic separations, this class of materials is attractive to explore under pressure. Here, we present the observation of direct to indirect band gap crossover and an insulator-metal transition in the vdW antiferromagnetic insulator CrPS 4 under pressure through in-situ photoluminescence, optical absorption, and resistivity measurements. Raman spectroscopy experiments revealed no changes in the spectral feature during the band gap crossover whereas the insulator-metal transition is possibly driven by the formation of the high-pressure crystal structure. Theoretical calculations suggest that the band gap crossover is driven by the shrinkage and rearrangement of the CrS 6 octahedra under pressure. Such high tunability under pressure demonstrates an interesting interplay between structural, optical and magnetic degrees of freedom in CrPS 4 , and provides further opportunity for the development of devices based on tunable properties of 2D vdW magnetic materials.

A pressure-induced structural phase transition and its intimate link with the superconducting transition was studied for the first time in TiSe2 up to 40 GPa at room temperature using X-ray diffraction, transport measurement, and first-principles calculations. We demonstrate the occurrence of a first-order structural phase transition at 4 GPa from the standard trigonal structure (S.G.P3̅m1) to another trigonal structure (S-G-P3̅c1). Additionally, at 16 GPa, the P3̅c1 phase spontaneously transforms into a monoclinic C2/m phase, and above 24 GPa, the C2/m phase returns to the initial P3̅m1 phase. Electrical transport results show that metallization occurs above 6 GPa. The charge density wave observed at ambient pressure is suppressed upon compression up to 2 GPa with the emergence of superconductivity at 2.5 GPa, with a critical temperature (T c) of 2 K. A structural transition accompanies the emergence of superconductivity that persists up to 4 GPa. The results demonstrate that the pressure-induced phase transitions explored by the experiments along with the theoretical predictions may open the door to a new path for searching and controlling the phase diagrams of transition metal dichalcogenides.

We report the superconductivity enhancement of ZrTe on compression up to 33 GPa. The superconducting transition occurs above 4.1 GPa and the superconducting temperature (T ) increases with pressure in further compression, reaching a maximum of 7.1 K at ~28 GPa. An anomalous change of superconducting temperature is seen in the compression above 21 GPa. No structural phase transition is observed in the whole compression up to 36 GPa, but a subtle change in structural parameter is seen between 17-19 GPa, which seems relevant to the anomalous increase in the superconducting temperature. First-principle calculations reveal that the density of states at the Fermi level increases with pressure, which explains the enhancement of T in ZrTe under compression.

Abstract. We have determined the magnetic structure of the intermetallic compound HoGa by high-resolution neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and the magnetic structure comprises ferromagnetic order of the Ho sublattice along the c-axis. The Curie temperature is 66(3) K. Upon cooling below 20 K, the Ho magnetic moments cant away from the c-axis towards the ab-plane. At 3 K, the Ho moment is 8.8(2) µB and the Ho magnetic moments point in the direction θ = 30(2)• and φ = 49(4)• with respect to the crystallographic c-axis. The observation of an ab-plane component at around 50• from the a-axis is in contrast with the suggested magnetic structure of ac order (θ = 32• and φ = 0 • ) reported by Delyagin et al.[1] on the basis of a 119 Sn Mössbauer spectroscopy study of a Sn-doped HoGa sample. However, we find that these two sets of orientations are in fact indistinguishable by Mössbauer spectroscopy.