Influence of spin-phonon coupling on antiferromagnetic spin fluctuations in FeSe under pressure: First-principles calculations with van der Waals corrections

摘要

The electronic structures, lattice dynamics, and magnetic properties of crystal β-FeSe under hydrostatic pressure have been studied by using the first-principles electronic structure calculations with van der Waals corrections. With applied pressure, the energy bands around the Fermi energy level consisting mainly of Fe-3d orbitals show obvious energy shifts and occupation variations, and meanwhile the frequencies of all optical phonon modes increase. Among these phonon modes, the A_(18) mode, which relates to the Se height from the Fe-Fe plane, shows a clear frequency jump in a pressure range between 5 and 6 GPa. This is also the pressure range within which the highest superconducting transition temperature T_c of FeSe is reached in experiments. In comparison with other phonon modes, the atomic displacement due to the zero-point vibration of the A_(1g) mode induces the strongest fluctuation of local magnetic moment on Fe under pressures from 0 to 9 GPa, and the induced fluctuation reaches a maximum around 5 GPa. These results suggest that the effect of phonon via spin-phonon coupling could not be completely omitted when exploring the superconducting mechanism in iron-based superconductors.