Dielectric Response of Electron-doped Ionic Superconductor Li$_x$ZrNCl

TL;DR

This study calculates the dielectric response of electron-doped ZrNCl, revealing how doping affects its electronic properties and plasmon peaks, with implications for understanding its superconductivity.

Contribution

It provides detailed calculations of dielectric properties across doping levels, comparing modeling approaches and linking electronic response to superconducting behavior.

Findings

Static dielectric constant matches experimental value

Main plasmon peaks are consistent with electron gas model

Doping level variations do not correlate with T_c changes

Abstract

When electron doped, the layered transition metal nitrides ${\cal T}$NCl (${\cal T}$ = group IVB transition metal ion) become impressive superconductors with critical temperature T$_c$= 15-26K. Here we take the most studied member, ZrNCl, as a representative and calculate the dielectric response $\epsilon(\omega)$ versus frequency and concentration of doped electronic carriers. The static dielectric constant $\epsilon_{\infty}$=5 is reproduced extremely well. We establish that the differences between rigid band modeling and virtual crystal treatment are small, and compare also with actual lithium doping using supercells. We obtain the variations upon changing the doping level of the reflectivity and energy loss function as well, many of which are found not to be correlated with the observed (non)variation of T$_c(x)$. The main plasmon peaks appear where the electron gas model suggests, in the range 1.2-2.0 eV for $x$ varying from 0.16 to 0.50.