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

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.

8 pages, 7 figures

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• Unconventional Superconductivity in electron-doped layered metal nitride halides $M$N$X$ ($M$ = Ti, Zr, Hf; $X$ = Cl, Br, I)
• Structural, Elastic, Electronic, and Optical Properties of Layered TiNX (X = F, Cl, Br, I) Compounds: a Density Functional Theory Study
• Modeling Intercalated Group-4-Metal Nitride Halide Superconductivity with Interlayer Coulomb Coupling
• μ-PES Studies on TiNCl and Quasi-two-dimensional Superconductor Na-intercalated TiNCl
• Soft x-ray irradiation induced metallization of layered TiNCl
• Dielectric Response of Electron-doped Ionic Superconductor Li${}_x$ZrNCl