Calculation of the nonlinear response functions of intra-exciton transitions in two-dimensional transition metal dichalcogenides

TL;DR

This paper develops a novel theoretical approach to calculate third-order nonlinear optical responses of intra-exciton transitions in 2D transition metal dichalcogenides, revealing dark states through two-photon absorption analysis.

Contribution

It introduces new methods combined with a variational approach to describe excitonic states and general formulas for third-order processes in 2D materials.

Findings

Calculated third-order nonlinear responses for WSe2.

Identified dark excitonic states via two-photon absorption.

Validated the theory with a circular well benchmark.

Abstract

In this paper, we study the third-order nonlinear optical response due to transitions between excitonic levels in two-dimensional transition metal dichalcogeniedes. To accomplish this, we use methods not applied to the description of excitons in two-dimensional materials so far and combined with a variational approach to describe the $1s$ excitonic state. The aforementioned transitions allow to probe dark states which are not revealed in absorption experiments. We present general formulas capable of describing any third-order process. The specific case of two-photon absorption in WSe2 is studied. The case of the circular well is also studied as a benchmark of the theory.