First-principles study on the magnetic and electronic properties of the high-pressure orthorhombic phase of MnSe

Exploring the mechanism of unconventional superconductivity has been one of the most important topics in condensed matter physics, while studying the magnetic and electronic properties of the parent compounds of unconventional superconductors can provide helpful clues. Recently, superconductivity in the orthorhombic-phase MnSe was successfully induced by applying high pressure, which makes MnSe the second Mn-based superconductor after MnP. Based on the spin-polarized density functional theory calculations, we have studied the magnetic and electronic properties of the orthorhombic-phase MnSe under high pressure. We show that there may exist strong antiferromagnetic (AFM) fluctuations in a narrow energy window (less than 3 meV/Mn) among an AFM state dubbed AFM3 and a series of staggered n-mer AFM states. Here the n-mer means that a set of n adjacent spins on a line are parallelly aligned. In the AFM3 state and the n-mer AFM states, the Mn spins show AFM coupling along the x axis and ferromagnetic (FM) coupling along the y axis, but respectively host FM and staggered n-mer AFM correlations along the z axis. Our calculations indicate that the orthorhombic-phase MnSe exhibits a metallic behavior in the low-energy magnetic states, in good accordance with the previous experimental observations. We also map the calculated energies onto an effective Heisenberg model and obtain the exchange couplings J, whose values can serve as a reference for analyzing the data from magnetic measurements. Two usual mechanisms like Fermi surface nesting and electron-phonon coupling can be ruled out as the origin of superconductivity. The magnetic properties in the orthorhombic-phase MnSe under high pressure need future in-depth experimental examination.