# Anisotropic features in the electronic structure of the two-dimensional transition metal trichalcogenide TiS$_3$: electron doping and plasmons

## TL;DR

This study investigates the electronic structure and plasmon behavior of TiS$_3$ monolayers, revealing anisotropic features, effects of electron doping, and potential electronic instabilities at specific doping levels using first-principles calculations.

## Contribution

It provides a detailed analysis of anisotropic electronic properties and plasmon spectra in TiS$_3$, highlighting the impact of electron doping and spin-orbit coupling on its behavior.

## Key findings

- Electron doping can induce incommensurate charge or spin modulations.
- Highly anisotropic plasmons are supported with opposite anisotropy for electrons and holes.
- Doped systems with smaller x remain 2D metals without electronic instabilities.

## Abstract

Analysis of the band structure of TiS$_3$ single-layers suggests the possibility of changing their physical behaviour by injecting electron carriers. The anisotropy of the valence and conduction bands is explained in terms of their complex orbital composition. The nature of the Fermi surface and Lindhard response function for different doping concentrations is studied by means of first-principles DFT calculations. It is suggested that for electron doping levels $x$ (number of electrons per unit cell) $\sim$ 0.18-0.30$e^-$ the system could exhibit incommensurate charge or spin modulations which, however, would keep the metallic state whereas systems doped with smaller $x$ would be 2D metals without any electronic instability. The effect of spin-orbit coupling in the band dispersion is analysed. The DFT effective masses are used to study the plasmon spectrum from an effective low energy model. We find that this material supports highly anisotropic plasmons, with opposite anisotropy for the electron and hole bands.