Variationally optimized orbital approach to trions in two-dimensional materials

TL;DR

This paper introduces a variational method using 2D Slater-type orbitals to efficiently compute trion energies and wavefunctions in 2D materials, showing good agreement with existing methods and highlighting the importance of exchange interactions.

Contribution

The paper presents a novel variational approach with linear combinations of 2D STOs for accurate and efficient trion calculations in 2D materials, including effects of electron-hole exchange.

Findings

Ground-state trions are bound across parameter ranges.

Excited-state trions are bound at large mass ratios or screening lengths.

Electron-hole exchange significantly affects trion binding energies.

Abstract

In this work, trions in two-dimensional (2D) space are studied by variational method with trial wavefunctions being constructed by linear combinations of 2D slater-type orbitals (STOs). Via this method, trion energy levels and wavefunctions can be calculated efficiently with fairly good accuracy. We first apply this method to study trion energy levels in a 2D hydrogen-like system with respect to a wide range of mass ratios and screening lengths. We find that the ground-state trion is bound for the whole parameter range, and an excited-state trion with antisymmetric permutation of electrons with finite angular momentum is bound for large electron-hole mass ratios or long screening lengths. The binding energies of ground-state trions calculated by the present method agree well with those calculated by more sophisticated but computationally-demanding methods. We then calculate trion states in various monolayer transition metal dichalcogenides (TMDCs) by using this method with the inclusion of electron-hole exchange (EHX) interaction. For TMDCs, we found that the effect of EHX can be significant in determining the trion binding energy and the possible existence of stable excited-state trions.