Spin and Charge Fluctuations in the $\alpha$-structure Layered Nitride Superconductors

TL;DR

This study investigates the electronic, spin, and charge properties of TiNCl, a layered nitride superconductor, revealing that both spin and charge fluctuations are significant in its superconducting behavior.

Contribution

It provides a first-principles analysis of spin and charge fluctuations in TiNCl, highlighting their comparable roles in superconductivity within the $eta$-structure layered nitrides.

Findings

Spin fluctuations are not dominant in TiNCl.

Charge fluctuations are equally significant as spin fluctuations.

TiNCl is confirmed to be a nonmagnetic superconductor.

Abstract

To explore conditions underlying the superconductivity in electron-doped TiNCl where T$_c$ = 16 K, we calculate the electronic structure, Wannier functions and spin and charge susceptibilities using first-principles density functional theory. TiNCl is the first high-temperature superconductor discovered in the $\alpha $-structure of the layered transition-metal nitride family MNCl (M=Ti, Zr, Hf). We construct a tight-binding model based on Wannier functions derived from the band structure, and consider explicit electronic interactions in a multi-band Hubbard Hamiltonian, where the interactions are treated with the random phase approximation (RPA) to calculate spin and charge susceptibility. The results show that, consistent with TiNCl being a nonmagnetic material, spin fluctuations do not dominate over charge fluctuations and both may have comparable impact on the properties of the doped system.