Novel $J_{\rm{eff}}$=3/2 Metallic Phase and Unconventional Superconductivity in GaTa$_4$Se$_8$

TL;DR

This study combines theoretical and experimental methods to reveal a novel $J_{eff}=3/2$ metallic phase in GaTa$_4$Se$_8$, showing unconventional superconductivity potentially driven by these moments and suggesting doping could induce superconductivity.

Contribution

It provides the first evidence of $J_{eff}=3/2$ moments in a metallic state and links these moments to pressure-induced and doping-related unconventional superconductivity.

Findings

$J_{eff}=3/2$ moments persist in the metallic phase under high pressure.

RIXS spectra show destructive quantum interference characteristic of $J_{eff}=3/2$ states.

The metallic phase exhibits properties of an unconventional superconductor influenced by $J_{eff}=3/2$ moments.

Abstract

By means of density functional theory plus dynamical mean-field theory (DFT+DMFT) calculations and resonant inelastic x-ray scattering (RIXS) experiments, we investigate the high-pressure phases of the spin-orbit-coupled $J_{\rm{eff}}=3/2$ insulator GaTa$_4$Se$_8$. Its metallic phase, derived from the Mott state by applying pressure, is found to carry $J_{\rm{eff}}=3/2$ moments. The characteristic excitation peak in the RIXS spectrum maintains its destructive quantum interference of $J_{\rm{eff}}$ at the Ta $L_2$-edge up to 10.4 GPa. Our exact diagonalization based DFT+DMFT calculations including spin-orbit coupling also reveal that the $J_{\rm{eff}}=3/2$ character can be clearly identified under high pressure. These results establish the intriguing nature of the correlated metallic magnetic phase, which represents the first confirmed example of $J_{\rm{eff}}$=3/2 moments residing in a metal. They also indicate that the pressure-induced superconductivity is likely unconventional and influenced by these $J_{\rm{eff}}=3/2$ moments. Based on a self-energy analysis, we furthermore propose the possibility of doping-induced superconductivity related to a spin-freezing crossover.