Band gap crossover and insulator–metal transition in the compressed layered CrPS4

Abstract

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.

Exploring few and single layer CrPS4 with near-field infrared spectroscopy

“…CrPS 4 is a collinear antiferromagnet below T N = 36 K [24,34] with ferromagnetic interactions within the layers and weak antiferromagentic interactions between sheets [25][26][27]. Moreover, pressure drives an insulator to metal transition above 15 GPa [35]. Raman scattering reveals peculiar frequency vs. layer number trends, although the origin of these effects is unclear at this time [14].…”

Controlling Spin Orientation and Metamagnetic Transitions in Anisotropic van der Waals Antiferromagnet CrPS4 by Hydrostatic Pressure

“…No structural phase transition is observed under pressures up to 11.4 GPa, which is in agreement with previous Raman spectroscopy. [ 36 ] As discussed above, temperature and pressure have the same influence on MAE change. By comparing temperature‐ and pressure‐dependent lattice parameters, b and b / a are found to both decrease with increasing temperature and pressure (Figure 4b and Figure S2, Supporting Information), indicating that the compression of b plays a major role.…”

“…[ 64 ] An on‐site Hubbard term U = 2 eV was used for Cr‐ d orbitals. [ 36 ] The supercells containing 48 atoms were constructed, and the crystal was optimized until the forces put on ions were smaller than 10 −3 eV Å −1 . The plane‐wave cut‐off energy was taken as 450 eV, and a 4×4×4 k‐points sampling was set to ensure that the total energy difference in self‐consistency was less than 10 −5 eV.…”

“…The first high‐pressure experiment of CrPS 4 mainly studied electronic and optical properties under pressures up to 31 GPa, yet leaving magnetic properties unclear. [ 36 ] A recent study investigated the magnetism in CrPS 4 under pressure by direct measurements of temperature‐dependent magnetization along the b axis and specific heat. SRT was found to be rapidly suppressed by pressure, whereas Néel temperature T N decreased only slightly.…”

Connection between the semiconductor--superconductor transition and the spin-polarized superconducting phase in the honeycomb lattice

“…These studies give important knowledge about physics of systems in which the Dirac fermions are realized. Relevant examples of such systems are superconductors containing the honeycomb sublattices (e.g., FePSe 3 [34], CrPS 4 [35], CrSiTe 3 [36], SnPS 3 [37], or Cu 2 I 2 Se 6 [38]) as well as certain transition metal dichalcogenides [39]. However, also interfaces between Dirac semimetals and superconductors can reveal similar properties [40][41][42][43][44].…”