Raman and first-principles study of the pressure-induced Mott-insulator to metal transition in bulk FePS3

Metal Site Substitution and Role of the Dimer on Symmetry Breaking in FePS3 and CrPS4 under Pressure

“…We identify critical pressures by the appearance or disappearance of peaks, splittings or combinations, inflection points in the frequency vs pressure data, or changes in slope as discussed below. − We define P C1 = 6.0, and P C2 = 13.6 GPa. These critical pressures separate the ambient pressure (AP) phase from the two higher-pressure phases (HP-I and HP-II) of FePS 3 . ,,,, The transition regions are somewhat gradual and occasionally sluggish, a characteristic that we indicate with blurry phase boundary lines. The mode frequencies, symmetries, assignments, and displacement patterns of FePS 3 in the C 2/ m space group are summarized in Tables S1 and S2, Supporting Information.…”

“…While the Raman scattering spectrum is insensitive to P C1 , the infrared response reveals subtle changes in the slope of the modes in the frequency vs pressure data, consistent with the reported C 2/ m → C 2/ m -like structural transition. P C2 is different. ,, Most notably, the infrared phonons become screened due to the development of metallicity, so we can not follow their progression into HP-2 [Figure (c,d)]. On the other hand, there is a condensation of two Raman-active peaks near 260 cm –1 that clearly supports a symmetry increase [Figure (e,f)].…”

“…Figure summarizes the vibrational response of FePS 3 under pressure. This system hosts a C 2/ m space group at ambient conditions, so we expect 12 infrared-active modes (5 A u + 7 B u ) and 15 Raman-active modes (8 A g + 7 B g ) in the spectra. ,, There are a number of reports on the infrared spectrum of FePS 3 at ambient conditions as well as the Raman scattering response under pressure. ,− That said, there are no high-pressure infrared studies in the literature, attesting to the difficulty of these measurements. This is the primary distinction of our work on FePS 3 .…”

High pressure tuning of magnon-polarons in the layered antiferromagnet FePS$_3$

“…S2 of the supplementary material a comparison with a simpler Hamiltonian based on a 3 × 3 matrix. One can also note that despite the difference in the involved energies (structural vs magnetic), this magnon-polaron resonance occurs at a pressure comparable to that of the first structural transition in bulk FePS 3 [23,31]. For pressures above P= 4.6 GPa where the structural phase transition is expected, the low-energy phonon spectrum (below 180 cm −1 ) changes significantly: the energy of P 1 decreases and is lower than the one at ambient pressure (E 1 = 80 cm −1 at P= 8.7 GPa), the energies of P 2 and of P 3 continue increasing but with a lower rate.…”

“…Bulk FePS 3 shows two structural phase transitions under pressure [23,28]: a first one close to P ∼ 4 GPa where the system transforms into a second C2/m phase named HP-I, and another one above P ∼ 14 GPa labelled HP-II in which bulk FePS 3 transforms to a metallic trigonal P31m phase. These phases have recently been explored by Raman scattering at room temperature [31] and the critical pressure corresponding to the first transition has been determined to be P = 4.6 GPa. The magnetic properties of these phases have been described by neutron scattering under high pressure [32][33][34].…”