Dimensionality switching and superconductivity transition in dense 1T−HfSe2

Pressure-induced phase transition and electronic structure evolution in layered semimetal HfTe2

“…Here, it should be noted that all atoms occupy various crystallographic 4m sites in this predicted C2/m-HfTe 2 , which is different from the previously reported high-pressure C2/m structures for TiTe 2 [52] and HfSe 2 . [32] At higher pressure points of 15 GPa, 25 GPa, and 50 GPa, our structure searches discover a new stable hexagonal P 62m structure (3 f.u./cell) [Fig. 1(c)] containing the building block of irregular HfTe 9 tetrakaidecahedron.…”

“…Combined with various experimental techniques including Raman spectra, optical absorption and resistance measurements as well as x-ray diffraction (XRD), pressure-driven metallization and superconductivity in HfSe 2 have been revealed in recent experimental works. [31][32][33] Two independent experimental works executed by Li et al [31] and Huang et al [32] found that the 1T -HfSe 2 transformed to a monoclinic C2/m intermediate structure above 11.2 GPa and then to a tetragonal I4/mmm structure above 45.5 GPa. However, Gao and Wang et al [33] proposed that the 1T -HfSe 2 undergoes a phase transition from the trigonal P 3m1 to a hexagonal P6 3 /mmc phase near 24 GPa.…”

Origin of the decompression driven superconductivity enhancement in SnSe2

“…50 Also, recent studies on HfSe 2 have found that the transformation of HfSe 2 from an anisotropic 2D structure to a quasi-3D crystal network can be partially preserved upon decompression to atmospheric pressure, which proves that interlayer bonding can be maintained to a low-pressure range in layered dichalcogenides. 51 Thus, the metallic state and superconductivity of SnSe 2 under pressure are mainly due to the change in electronic structure caused by the Se-Se bonding between the layers. The interlayer Se-Se bonding is more stable than the weak van der Waals bonding and can therefore be maintained to a lower pressure range during decompression to the extent that high carrier concentrations can be maintained.…”

Pressure-driven structural phase transitions and metallization in the two-dimensional ferromagnetic semiconductor CrBr3

“…In contrast to CrCl 3 and CrBr 3 , the absence of structural transition in CrI 3 up to ∼40.0 GPa is presumably related to the more delocalized 5p orbitals of the iodine atom than the 3p and 4p orbitals of chlorine and bromine atoms, which leads to better hybridization of chromium 3d and iodine 5p orbitals and thus stronger interlayer interactions. [34][35][36] Besides, unlike the abrupt enhancement in the electrical conductivity of CrCl 3 and CrBr 3 at around metallization, the progressive increase of electrical conductivity in CrI 3 indicated the continuous tunability of its electronic structure and bandgap energy under high pressure. Furthermore, more detailed comparisons of the pressures of structural and electronic transitions for CrX 3 compounds upon compression and decompression under different hydrostatic conditions are listed in Table S5.…”